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initial commit for java style guide
This commit is contained in:
eh@google.com
parent
1968027290
commit
b631371099
507
javaguide.css
Normal file
507
javaguide.css
Normal file
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@ -0,0 +1,507 @@
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table {
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border-collapse: collapse;
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}
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td, th {
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border: 1px solid #ccc;
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padding: 2px 12px;
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font-size: 10pt;
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}
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code, samp, var {
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color: #060;
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}
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pre {
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font-size: 10pt;
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display: block;
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color: #060;
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background-color: #e8fff6;
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border-color: #f0fff0;
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border-style: solid;
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border-top-width: 1px;
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border-bottom-width: 1px;
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border-right-width: 1px;
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border-left-width: 5px;
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padding-left: 12px;
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padding-right: 12px;
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padding-top: 4px;
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padding-bottom: 4px;
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}
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pre.badcode {
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color: #c00;
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background-color: #ffe6d8;
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border-color: #fff0f0;
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}
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hr {
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margin-top: 3.5em;
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border-width: 1px;
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color: #fff;
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}
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html {
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margin-top:2em;
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margin-left:10%;
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margin-right:10%;
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padding:0;
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}
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.bp-reset-element,
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body,
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h1,
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h2,
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h3,
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h4,
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h5,
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h6,
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article,
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aside,
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details,
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figcaption,
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figure,
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footer,
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header,
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hgroup,
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menu,
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nav,
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section,
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summary,
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blockquote,
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q,
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th,
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td,
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caption,
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table,
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div,
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span,
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object,
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iframe,
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p,
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pre,
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a,
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abbr,
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acronym,
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address,
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code,
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del,
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dfn,
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em,
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img,
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dl,
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dt,
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dd,
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ol,
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ul,
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li,
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fieldset,
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form,
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label,
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legend,
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caption,
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tbody,
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tfoot,
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thead,
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tr {
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margin:0;
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padding:0;
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border:0;
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font-weight:inherit;
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font-style:inherit;
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font-size:100%;
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font-family:inherit;
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vertical-align:baseline;
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}
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body {
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font-family:'Arial', sans-serif;
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font-size:81.25%;
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color:#222;
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background-color:#fff;
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line-height:1.67;
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overflow: auto;
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}
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.change {
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text-align: right;
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margin-bottom:1em;
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}
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h1,
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h2,
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h3,
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h4,
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h5,
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h6 {
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font-weight:bold;
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}
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h1 {
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margin-bottom:.50em;
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text-align: center
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}
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h2,
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h3,
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h4,
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h5,
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h6 {
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margin-top:1.5em;
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margin-bottom:.75em;
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}
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h1 {font-size:200%;}
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h2 {font-size:167%;}
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h3 {font-size:133%;}
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h4 {font-size:120%;}
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h5 {font-size:110%;}
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p {
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margin:0 0 1.5em;
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}
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a[href=''] {
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cursor:default;
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}
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h1 img,
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h2 img,
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h3 img,
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h4 img,
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h5 img,
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h6 img {
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margin:0;
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}
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a img {
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border:none;
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}
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pre {
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margin:1.5em 0;
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white-space:pre;
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}
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pre,
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code,
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kbd,
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tt {
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font:1em 'Droid Sans Mono', monospace;
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line-height:1.5;
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}
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dl {
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margin:0 0 1.5em 0;
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}
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dl dt {
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font-weight:bold;
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}
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dd {
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margin-left:1.5em;
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}
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hr {
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height:0;
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border:0;
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border-top:1px solid #ccc;
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background-color:#ccc;
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}
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table {
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border:1px solid #bbb;
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border-spacing:0;
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border-collapse:collapse;
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margin:0 0 1.5em;
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vertical-align:middle;
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width:100%;
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}
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table.unlined,
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table.unlined th,
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table.unlined tr,
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table.unlined td {
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border:0;
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}
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th,
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td,
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caption {
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float:none !important;
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text-align:left;
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font-weight:normal;
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vertical-align:middle;
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padding:4px;
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}
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caption {
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padding:0;
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}
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td {
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border:1px solid #bbb;
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vertical-align:top;
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}
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th {
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border:0;
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border-bottom:1px solid black;
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font-weight:bold;
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background:rgb(229, 236, 249);
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}
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table th code {
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background-color:inherit;
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color:inherit;
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}
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table tfoot th {
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border:1px solid #bbb;
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}
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tfoot {
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font-style:italic;
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}
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caption {
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background:#eee;
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}
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table[border='0'] {
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border:none;
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}
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table[border='0']>tbody>tr>td,
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table[border='0']>tr>td {
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border:none;
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}
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tr.alt td,
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td.alt {
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background-color:#efefef;
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}
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table.striped tr:nth-child(even) td,
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table tr.even td {
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background:#efefef;
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}
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table.columns {
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border:none;
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}
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table.columns>tbody>tr>td,
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table.columns>tr>td {
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border:none;
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padding:0 3em 0 0;
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}
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table.columns>tbody>tr>td:last-child,
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table.columns>tr>td:last-child {
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border:none;
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padding:0;
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}
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ul,
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ol {
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margin:0 1.5em 1.5em 0;
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padding-left:2em;
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}
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li ul,
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li ol {
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margin:0;
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}
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ul {
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list-style-type:disc;
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}
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ol {
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list-style-type:decimal;
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}
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ul {
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list-style-type:disc;
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}
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ul ul {
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list-style-type:circle;
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}
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ul ul ul {
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list-style-type:square;
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}
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ul.disc {
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list-style-type:disc;
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}
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ul.circle {
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list-style-type:circle;
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}
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ul.square {
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list-style-type:square;
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}
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ol {
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list-style-type:decimal;
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}
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ol ol {
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list-style-type:lower-alpha;
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}
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ol ol ol {
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list-style-type:lower-roman;
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}
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ol ul {
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list-style-type:circle;
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}
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ol.decimal {
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list-style-type:decimal;
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}
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ol.upper-alpha {
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list-style-type:upper-alpha;
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}
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ol.lower-alpha {
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list-style-type:lower-alpha;
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}
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ol.upper-roman {
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list-style-type:upper-roman;
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}
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ol.lower-roman {
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list-style-type:lower-roman;
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}
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ol.nolist,
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ul.nolist {
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padding-left:0;
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list-style-image:none;
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list-style-type:none;
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margin-left:0;
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}
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.center {
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text-align:center;
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}
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code,
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kbd,
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pre {
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color:#007000;
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}
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kbd {
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font-weight: bold;
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}
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table.striped code {
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background-color:inherit;
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|
}
|
||||||
|
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pre {
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padding:6px 10px;
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background-color:#FAFAFA;
|
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border:1px solid #bbb;
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overflow:auto;
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}
|
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|
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||||||
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pre.prettyprint {
|
||||||
|
padding:6px 10px !important;
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||||||
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border:1px solid #bbb !important;
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}
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code.bad, code.badcode {
|
||||||
|
background-color:#fcc;
|
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}
|
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pre.bad, pre.badcode {
|
||||||
|
background-color:#fcc;
|
||||||
|
border-top:1px inset #a03;
|
||||||
|
border-left:1px inset #a03;
|
||||||
|
}
|
||||||
|
|
||||||
|
.tip {
|
||||||
|
background-color:#fffbd9;
|
||||||
|
padding:6px 8px 6px 10px;
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||||||
|
border-left:6px solid #ffef70;
|
||||||
|
}
|
||||||
|
|
||||||
|
.note {
|
||||||
|
background-color:#e5ecf9;
|
||||||
|
padding:6px 8px 6px 10px;
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||||||
|
border-left:6px solid #36c;
|
||||||
|
}
|
||||||
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|
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@media print {
|
||||||
|
|
||||||
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.str {
|
||||||
|
color:#060;
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}
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||||||
|
|
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.kwd {
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||||||
|
color:#006;
|
||||||
|
font-weight:bold;
|
||||||
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}
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||||||
|
|
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.com {
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||||||
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color:#600;
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||||||
|
font-style:italic;
|
||||||
|
}
|
||||||
|
|
||||||
|
.typ {
|
||||||
|
color:#404;
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||||||
|
font-weight:bold;
|
||||||
|
}
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||||||
|
|
||||||
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.lit {
|
||||||
|
color:#044;
|
||||||
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}
|
||||||
|
|
||||||
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.pun,
|
||||||
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.opn,
|
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.clo {
|
||||||
|
color:#440;
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||||||
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}
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||||||
|
|
||||||
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.pln {
|
||||||
|
color:#000;
|
||||||
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}
|
||||||
|
|
||||||
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.tag {
|
||||||
|
color:#006;
|
||||||
|
font-weight:bold;
|
||||||
|
}
|
||||||
|
|
||||||
|
.atn {
|
||||||
|
color:#404;
|
||||||
|
}
|
||||||
|
|
||||||
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.atv {
|
||||||
|
color:#060;
|
||||||
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}
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||||||
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|
||||||
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h1 {
|
||||||
|
font-style:italic;
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
ol.linenums {
|
||||||
|
margin-top:0;
|
||||||
|
margin-bottom:0;
|
||||||
|
}
|
||||||
|
|
||||||
|
code {
|
||||||
|
background-color:#FAFAFA;
|
||||||
|
padding: 0.25em 0.5em;
|
||||||
|
white-space: nowrap
|
||||||
|
}
|
||||||
665
javaguide.html
Normal file
665
javaguide.html
Normal file
|
|
@ -0,0 +1,665 @@
|
||||||
|
<html lang="en">
|
||||||
|
<head>
|
||||||
|
<meta http-equiv="content-type" content="text/html; charset=UTF-8" />
|
||||||
|
<link rel="stylesheet" type="text/css" href="javaguide.css"/>
|
||||||
|
<script src="http://google-code-prettify.googlecode.com/svn/loader/run_prettify.js"
|
||||||
|
type="text/javascript"></script>
|
||||||
|
<link href="http://www.google.com/favicon.ico"
|
||||||
|
type="image/x-icon" rel="shortcut icon" />
|
||||||
|
<title>Google Java Style</title>
|
||||||
|
</head>
|
||||||
|
<body>
|
||||||
|
<h1>Google Java Style</h1>
|
||||||
|
<div class="change">Last changed: December 17, 2013</div>
|
||||||
|
<table border="0">
|
||||||
|
<tr>
|
||||||
|
<td>
|
||||||
|
<dl>
|
||||||
|
<dt>
|
||||||
|
<a href="#s1-introduction">1 Introduction</a>
|
||||||
|
</dt>
|
||||||
|
<dd>
|
||||||
|
<a href="#s1.1-terminology">1.1 Terminology notes</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s1.2-guide-notes">1.2 Guide notes</a>
|
||||||
|
</dd>
|
||||||
|
<dt>
|
||||||
|
<a href="#s2-source-file-basics">2 Source file basics</a>
|
||||||
|
</dt>
|
||||||
|
<dd>
|
||||||
|
<a href="#s2.1-file-name">2.1 File name</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s2.2-file-encoding">2.2 File encoding: UTF-8</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s2.3-special-characters">2.3 Special characters</a>
|
||||||
|
</dd>
|
||||||
|
<dt>
|
||||||
|
<a href="#s3-source-file-structure">3 Source file structure</a>
|
||||||
|
</dt>
|
||||||
|
<dd>
|
||||||
|
<a href="#s3.1-copyright-statement">3.1 License or copyright information, if present</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s3.2-package-statement">3.2 Package statement</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s3.3-import-statements">3.3 Import statements</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s3.4-class-declaration">3.4 Class declaration</a>
|
||||||
|
</dd>
|
||||||
|
</dl>
|
||||||
|
</td><td>
|
||||||
|
<dl>
|
||||||
|
<dt>
|
||||||
|
<a href="#s4-formatting">4 Formatting</a>
|
||||||
|
</dt>
|
||||||
|
<dd>
|
||||||
|
<a href="#s4.1-braces">4.1 Braces</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s4.2-block-indentation">4.2 Block indentation: +2 spaces</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s4.3-one-statement-per-line">4.3 One statement per line</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s4.4-column-limit">4.4 Column limit: 80 or 100</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s4.5-line-wrapping">4.5 Line-wrapping</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s4.6-whitespace">4.6 Whitespace</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s4.7-grouping-parentheses">4.7 Grouping parentheses: recommended</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s4.8-specific-constructs">4.8 Specific constructs</a>
|
||||||
|
</dd>
|
||||||
|
<dt>
|
||||||
|
<a href="#s5-naming">5 Naming</a>
|
||||||
|
</dt>
|
||||||
|
<dd>
|
||||||
|
<a href="#s5.1-identifier-names">5.1 Rules common to all identifiers</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s5.2-specific-identifier-names">5.2 Rules by identifier type</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s5.3-camel-case">5.3 Camel case: defined</a>
|
||||||
|
</dd>
|
||||||
|
</dl>
|
||||||
|
</td><td>
|
||||||
|
<dl>
|
||||||
|
<dt>
|
||||||
|
<a href="#s6-programming-practices">6 Programming Practices</a>
|
||||||
|
</dt>
|
||||||
|
<dd>
|
||||||
|
<a href="#s6.1-override-annotation">6.1 @Override: always used</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s6.2-caught-exceptions">6.2 Caught exceptions: not ignored</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s6.3-static-members">6.3 Static members: qualified using class</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s6.4-finalizers">6.4 Finalizers: not used</a>
|
||||||
|
</dd>
|
||||||
|
<dt>
|
||||||
|
<a href="#s7-javadoc">7 Javadoc</a>
|
||||||
|
</dt>
|
||||||
|
<dd>
|
||||||
|
<a href="#s7.1-javadoc-formatting">7.1 Formatting</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s7.2-summary-fragment">7.2 The summary fragment</a>
|
||||||
|
</dd>
|
||||||
|
<dd>
|
||||||
|
<a href="#s7.3-javadoc-where-required">7.3 Where Javadoc is used</a>
|
||||||
|
</dd>
|
||||||
|
</dl>
|
||||||
|
</td>
|
||||||
|
</tr>
|
||||||
|
</table>
|
||||||
|
<div><div id="with-header-links"><a name="s1-introduction"/>
|
||||||
|
<h2>1 Introduction <a href="#s1-introduction"><img height="21" width="21" src="javaguidelink.png"/></a></h2>
|
||||||
|
<p>This document serves as the <strong>complete</strong> definition of Google's coding standards for
|
||||||
|
source code in the Java™ Programming Language. A Java source file is described as being <em>in
|
||||||
|
Google Style</em> if and only if it adheres to the rules herein.</p><p>Like other programming style guides, the issues covered span not only aesthetic issues of
|
||||||
|
formatting, but other types of conventions or coding standards as well. However, this document
|
||||||
|
focuses primarily on the <strong>hard-and-fast rules</strong> that we follow universally, and
|
||||||
|
avoids giving <em>advice</em> that isn't clearly enforceable (whether by human or tool).
|
||||||
|
</p><a name="s1.1-terminology"/>
|
||||||
|
<h3>1.1 Terminology notes <a href="#s1.1-terminology"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>In this document, unless otherwise clarified:</p><ol><li>The term <em>class</em> is used inclusively to mean an "ordinary" class, enum class,
|
||||||
|
interface or annotation type (<code class="prettyprint lang-java">@interface</code>).</li><li>The term <em>comment</em> always refers to <em>implementation</em> comments. We do not
|
||||||
|
use the phrase "documentation comments", instead using the common term "Javadoc."</li></ol><p>Other "terminology notes" will appear occasionally throughout the document.</p><a name="s1.2-guide-notes"/>
|
||||||
|
<h3>1.2 Guide notes <a href="#s1.2-guide-notes"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>Example code in this document is <strong>non-normative</strong>. That is, while the examples
|
||||||
|
are in Google Style, they may not illustrate the <em>only</em> stylish way to represent the
|
||||||
|
code. Optional formatting choices made in examples should not be enforced as rules.</p><a name="s2-source-file-basics"/>
|
||||||
|
<h2>2 Source file basics <a href="#s2-source-file-basics"><img height="21" width="21" src="javaguidelink.png"/></a></h2>
|
||||||
|
<a name="s2.1-file-name"/>
|
||||||
|
<h3>2.1 File name <a href="#s2.1-file-name"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>The source file name consists of the case-sensitive name of the top-level class it contains,
|
||||||
|
plus the <code>.java</code> extension (aside from <code>package-info.java</code> files).</p><a name="s2.2-file-encoding"/>
|
||||||
|
<h3>2.2 File encoding: UTF-8 <a href="#s2.2-file-encoding"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>Source files are encoded in <strong>UTF-8</strong>.</p><a name="s2.3-special-characters"/>
|
||||||
|
<h3>2.3 Special characters <a href="#s2.3-special-characters"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<a name="s2.3.1-whitespace-characters"/>
|
||||||
|
<h4>2.3.1 Whitespace characters <a href="#s2.3.1-whitespace-characters"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Aside from the line terminator sequence, the <strong>ASCII horizontal space
|
||||||
|
character</strong> (<strong>0x20</strong>) is the only whitespace character that appears
|
||||||
|
anywhere in a source file. This implies that:</p><ol><li>All other whitespace characters in string and character literals are escaped.</li><li>Tab characters are <strong>not</strong> used for indentation.</li></ol><a name="s2.3.2-special-escape-sequences"/>
|
||||||
|
<h4>2.3.2 Special escape sequences <a href="#s2.3.2-special-escape-sequences"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>For any character that has a special escape sequence
|
||||||
|
(<code class="prettyprint lang-java">\b</code>,
|
||||||
|
<code class="prettyprint lang-java">\t</code>,
|
||||||
|
<code class="prettyprint lang-java">\n</code>,
|
||||||
|
<code class="prettyprint lang-java">\f</code>,
|
||||||
|
<code class="prettyprint lang-java">\r</code>,
|
||||||
|
<code class="prettyprint lang-java">\"</code>,
|
||||||
|
<code class="prettyprint lang-java">\'</code> and
|
||||||
|
<code class="prettyprint lang-java">\\</code>), that sequence
|
||||||
|
is used rather than the corresponding octal
|
||||||
|
(e.g. <code class="prettyprint lang-java badcode">\012</code>) or Unicode
|
||||||
|
(e.g. <code class="prettyprint lang-java badcode">\u000a</code>) escape.</p><a name="s2.3.3-non-ascii-characters"/>
|
||||||
|
<h4>2.3.3 Non-ASCII characters <a href="#s2.3.3-non-ascii-characters"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>For the remaining non-ASCII characters, either the actual Unicode character
|
||||||
|
(e.g. <code class="prettyprint lang-java">∞</code>) or the equivalent Unicode escape
|
||||||
|
(e.g. <code class="prettyprint lang-java">\u221e</code>) is used, depending only on which
|
||||||
|
makes the code <strong>easier to read and understand</strong>.</p><p class="tip"><b>Tip:</b> in the Unicode escape case, and occasionally even when actual Unicode characters
|
||||||
|
are used, an explanatory comment can be very helpful.</p><p>Examples:</p><table><tr><th>Example</th><th>Discussion</th></tr><tr><td><code class="prettyprint lang-java">String unitAbbrev = "μs";</code></td><td>Best: perfectly clear even without a comment.</td></tr><tr><td><code class="prettyprint lang-java">String unitAbbrev = "\u03bcs"; // "μs"</code></td><td>Allowed, but there's no reason to do this.</td></tr><tr><td><code class="prettyprint lang-java">String unitAbbrev = "\u03bcs";
|
||||||
|
// Greek letter mu, "s"</code></td><td>Allowed, but awkward and prone to mistakes.</td></tr><tr><td><code class="prettyprint lang-java badcode">String unitAbbrev = "\u03bcs";</code></td><td>Poor: the reader has no idea what this is.</td></tr><tr><td><code class="prettyprint lang-java">return '\ufeff' + content;
|
||||||
|
// byte order mark</code></td><td>Good: use escapes for non-printable characters, and comment if necessary.</td></tr></table><p class="tip"><b>Tip:</b> Never make your code less readable simply out of fear that some programs might
|
||||||
|
not handle non-ASCII characters properly. If that should happen, those programs
|
||||||
|
are <strong>broken</strong> and they must be <strong>fixed</strong>.</p><a name="filestructure"/><a name="s3-source-file-structure"/>
|
||||||
|
<h2>3 Source file structure <a href="#s3-source-file-structure"><img height="21" width="21" src="javaguidelink.png"/></a></h2>
|
||||||
|
<div><p>A source file consists of, <strong>in order</strong>:</p><ol><li>License or copyright information, if present</li><li>Package statement</li><li>Import statements</li><li>Exactly one top-level class</li></ol></div><p><strong>Exactly one blank line</strong> separates each section that is present.</p><a name="s3.1-copyright-statement"/>
|
||||||
|
<h3>3.1 License or copyright information, if present <a href="#s3.1-copyright-statement"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>If license or copyright information belongs in a file, it belongs here.</p><a name="s3.2-package-statement"/>
|
||||||
|
<h3>3.2 Package statement <a href="#s3.2-package-statement"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>The package statement is <strong>not line-wrapped</strong>. The column limit (Section 4.4,
|
||||||
|
<a href="#s4.4-column-limit">Column limit: 80 or 100</a>) does not apply to package statements.</p><a name="imports"/><a name="s3.3-import-statements"/>
|
||||||
|
<h3>3.3 Import statements <a href="#s3.3-import-statements"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<a name="s3.3.1-wildcard-imports"/>
|
||||||
|
<h4>3.3.1 No wildcard imports <a href="#s3.3.1-wildcard-imports"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p><strong>Wildcard imports</strong>, static or otherwise, <strong>are not used</strong>.</p><a name="s3.3.2-import-line-wrapping"/>
|
||||||
|
<h4>3.3.2 No line-wrapping <a href="#s3.3.2-import-line-wrapping"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Import statements are <strong>not line-wrapped</strong>. The column limit (Section 4.4,
|
||||||
|
<a href="#s4.4-column-limit">Column limit: 80 or 100</a>) does not apply to import
|
||||||
|
statements.</p><a name="s3.3.3-import-ordering-and-spacing"/>
|
||||||
|
<h4>3.3.3 Ordering and spacing <a href="#s3.3.3-import-ordering-and-spacing"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Import statements are divided into the following groups, in this order, with each group
|
||||||
|
separated by a single blank line:</p><ol><li>All static imports in a single group</li><li><code>com.google</code> imports
|
||||||
|
(only if this source file is in the <code>com.google</code> package
|
||||||
|
space)</li><li>Third-party imports, one group per top-level package, in ASCII sort order
|
||||||
|
<ul><li>for example: <code>android</code>, <code>com</code>, <code>junit</code>, <code>org</code>,
|
||||||
|
<code>sun</code></li></ul></li><li><code>java</code> imports</li><li><code>javax</code> imports</li></ol><p>Within a group there are no blank lines, and the imported names appear in ASCII sort
|
||||||
|
order. (<strong>Note:</strong> this is not the same as the import <em>statements</em> being in
|
||||||
|
ASCII sort order; the presence of semicolons warps the result.)</p><a name="s3.4-class-declaration"/>
|
||||||
|
<h3>3.4 Class declaration <a href="#s3.4-class-declaration"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<a name="oneclassperfile"/><a name="s3.4.1-one-top-level-class"/>
|
||||||
|
<h4>3.4.1 Exactly one top-level class declaration <a href="#s3.4.1-one-top-level-class"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Each top-level class resides in a source file of its own.</p><p class="exception"><b>Exception:</b> of course, no such class appears in <code>package-info.java</code>
|
||||||
|
files.</p><a name="s3.4.2-class-member-ordering"/>
|
||||||
|
<h4>3.4.2 Class member ordering <a href="#s3.4.2-class-member-ordering"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>The ordering of the members of a class can have a great effect on learnability, but there is
|
||||||
|
no single correct recipe for how to do it. Different classes may order their members
|
||||||
|
differently.</p><p>What is important is that each class order its members in <strong><em>some</em> logical
|
||||||
|
order</strong>, which its maintainer could explain if asked. For example, new methods are not
|
||||||
|
just habitually added to the end of the class, as that would yield "chronological by date
|
||||||
|
added" ordering, which is not a logical ordering.</p><a name="overloads"/><a name="s3.4.2.1-overloads-never-split"/>
|
||||||
|
<h5>3.4.2.1 Overloads: never split <a href="#s3.4.2.1-overloads-never-split"><img height="21" width="21" src="javaguidelink.png"/></a></h5>
|
||||||
|
<p>When a class has multiple constructors, or multiple methods with the same name, these appear
|
||||||
|
sequentially, with no intervening members.</p><a name="s4-formatting"/>
|
||||||
|
<h2>4 Formatting <a href="#s4-formatting"><img height="21" width="21" src="javaguidelink.png"/></a></h2>
|
||||||
|
<p class="terminology"><b>Terminology Note:</b> <em>block-like construct</em> refers to the body of a class, method or
|
||||||
|
constructor. Note that, by Section 4.8.3.1 on
|
||||||
|
<a href="#s4.8.3.1-array-initializers">array initializers</a>, any array initializer
|
||||||
|
<em>may</em> optionally be treated as if it were a block-like construct.</p><a name="braces"/><a name="s4.1-braces"/>
|
||||||
|
<h3>4.1 Braces <a href="#s4.1-braces"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<a name="s4.1.1-braces-always-used"/>
|
||||||
|
<h4>4.1.1 Braces are used where optional <a href="#s4.1.1-braces-always-used"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Braces are used with
|
||||||
|
<code class="prettyprint lang-java">if</code>,
|
||||||
|
<code class="prettyprint lang-java">else</code>,
|
||||||
|
<code class="prettyprint lang-java">for</code>,
|
||||||
|
<code class="prettyprint lang-java">do</code> and
|
||||||
|
<code class="prettyprint lang-java">while</code> statements, even when the
|
||||||
|
body is empty or contains only a single statement.</p><a name="s4.1.2-blocks-k-r-style"/>
|
||||||
|
<h4>4.1.2 Nonempty blocks: K & R style <a href="#s4.1.2-blocks-k-r-style"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Braces follow the Kernighan and Ritchie style
|
||||||
|
("<a href="http://www.codinghorror.com/blog/2012/07/new-programming-jargon.html">Egyptian brackets</a>")
|
||||||
|
for <em>nonempty</em> blocks and block-like constructs:</p><ul><li>No line break before the opening brace.</li><li>Line break after the opening brace.</li><li>Line break before the closing brace.</li><li>Line break after the closing brace <em>if</em> that brace terminates a statement or the body
|
||||||
|
of a method, constructor or <em>named</em> class. For example, there is <em>no</em> line break
|
||||||
|
after the brace if it is followed by <code class="prettyprint lang-java">else</code> or a
|
||||||
|
comma.</li></ul><p>Example:</p><pre class="prettyprint lang-java">
|
||||||
|
return new MyClass() {
|
||||||
|
@Override public void method() {
|
||||||
|
if (condition()) {
|
||||||
|
try {
|
||||||
|
something();
|
||||||
|
} catch (ProblemException e) {
|
||||||
|
recover();
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
||||||
|
};
|
||||||
|
</pre><p>A few exceptions for enum classes are given in Section 4.8.1,
|
||||||
|
<a href="#s4.8.1-enum-classes">Enum classes</a>.</p><a name="emptyblocks"/><a name="s4.1.3-braces-empty-blocks"/>
|
||||||
|
<h4>4.1.3 Empty blocks: may be concise <a href="#s4.1.3-braces-empty-blocks"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>An empty block or block-like construct <em>may</em> be closed immediately after it is
|
||||||
|
opened, with no characters or line break in between
|
||||||
|
(<code class="prettyprint lang-java">{}</code>), <strong>unless</strong> it is part of a
|
||||||
|
<em>multi-block statement</em> (one that directly contains multiple blocks:
|
||||||
|
<code class="prettyprint lang-java">if/else-if/else</code> or
|
||||||
|
<code class="prettyprint lang-java">try/catch/finally</code>).</p><p>Example:</p><pre class="prettyprint lang-java">
|
||||||
|
void doNothing() {}
|
||||||
|
</pre><a name="s4.2-block-indentation"/>
|
||||||
|
<h3>4.2 Block indentation: +2 spaces <a href="#s4.2-block-indentation"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>Each time a new block or block-like construct is opened, the indent increases by two
|
||||||
|
spaces. When the block ends, the indent returns to the previous indent level. The indent level
|
||||||
|
applies to both code and comments throughout the block. (See the example in Section 4.1.2,
|
||||||
|
<a href="#s4.1.2-blocks-k-r-style">Nonempty blocks: K & R Style</a>.)</p><a name="s4.3-one-statement-per-line"/>
|
||||||
|
<h3>4.3 One statement per line <a href="#s4.3-one-statement-per-line"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>Each statement is followed by a line-break.</p><a name="columnlimit"/><a name="s4.4-column-limit"/>
|
||||||
|
<h3>4.4 Column limit: 80 or 100 <a href="#s4.4-column-limit"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>
|
||||||
|
Projects are free to choose a column limit of either 80 or 100 characters.
|
||||||
|
|
||||||
|
Except as noted below, any line that would exceed this limit must be line-wrapped, as explained in
|
||||||
|
Section 4.5, <a href="#s4.5-line-wrapping">Line-wrapping</a>.
|
||||||
|
</p><p><strong>Exceptions:</strong></p><ol><li>Lines where obeying the column limit is not possible (for example, a long URL in Javadoc,
|
||||||
|
or a long JSNI method reference).</li><li><code class="prettyprint lang-java">package</code> and
|
||||||
|
<code class="prettyprint lang-java">import</code> statements (see Sections
|
||||||
|
3.2 <a href="#s3.2-package-statement">Package statement</a> and
|
||||||
|
3.3 <a href="#s3.3-import-statements">Import statements</a>).</li><li>Command lines in a comment that may be cut-and-pasted into a shell.</li></ol><a name="s4.5-line-wrapping"/>
|
||||||
|
<h3>4.5 Line-wrapping <a href="#s4.5-line-wrapping"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p class="terminology"><b>Terminology Note:</b> When code that might otherwise legally occupy a single line is divided into
|
||||||
|
multiple lines, typically to avoid overflowing the column limit, this activity is called
|
||||||
|
<em>line-wrapping</em>.</p><p>There is no comprehensive, deterministic formula showing <em>exactly</em> how to line-wrap in
|
||||||
|
every situation. Very often there are several valid ways to line-wrap the same piece of code.</p><p class="tip"><b>Tip:</b> extracting a method or local variable may solve the problem without the need to
|
||||||
|
line-wrap.</p><a name="s4.5.1-line-wrapping-where-to-break"/>
|
||||||
|
<h4>4.5.1 Where to break <a href="#s4.5.1-line-wrapping-where-to-break"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>The prime directive of line-wrapping is: prefer to break at a
|
||||||
|
<strong>higher syntactic level</strong>. Also:</p><ol><li>When a line is broken at a <em>non-assignment</em> operator the break comes <em>before</em>
|
||||||
|
the symbol. (Note that this is not the same practice used in Google style for other languages,
|
||||||
|
such as C++ and JavaScript.)
|
||||||
|
<ul><li>This also applies to the following "operator-like" symbols: the dot separator
|
||||||
|
(<code class="prettyprint lang-java">.</code>), the ampersand in type bounds
|
||||||
|
(<code class="prettyprint lang-java"><T extends Foo & Bar></code>), and the pipe in
|
||||||
|
catch blocks
|
||||||
|
(<code class="prettyprint lang-java">catch (FooException | BarException e)</code>).</li></ul></li><li>When a line is broken at an <em>assignment</em> operator the break typically comes
|
||||||
|
<em>after</em> the symbol, but either way is acceptable.
|
||||||
|
<ul><li>This also applies to the "assignment-operator-like" colon in an enhanced
|
||||||
|
<code class="prettyprint lang-java">for</code> ("foreach") statement.</li></ul></li><li>A method or constructor name stays attached to the open parenthesis
|
||||||
|
(<code class="prettyprint lang-java">(</code>) that follows it.</li><li>A comma (<code class="prettyprint lang-java">,</code>) stays attached to the token that
|
||||||
|
precedes it.</li></ol><a name="indentation"/><a name="s4.5.2-line-wrapping-indent"/>
|
||||||
|
<h4>4.5.2 Indent continuation lines at least +4 spaces <a href="#s4.5.2-line-wrapping-indent"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>When line-wrapping, each line after the first (each <em>continuation line</em>) is indented
|
||||||
|
at least +4 from the original line.</p><p>When there are multiple continuation lines, indentation may be varied beyond +4 as
|
||||||
|
desired. In general, two continuation lines use the same indentation level if and only if they
|
||||||
|
begin with syntactically parallel elements.</p><p>Section 4.6.3 on <a href="#s4.6.3-horizontal-alignment">Horizontal alignment</a> addresses
|
||||||
|
the discouraged practice of using a variable number of spaces to align certain tokens with
|
||||||
|
previous lines.</p><a name="s4.6-whitespace"/>
|
||||||
|
<h3>4.6 Whitespace <a href="#s4.6-whitespace"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<a name="s4.6.1-vertical-whitespace"/>
|
||||||
|
<h4>4.6.1 Vertical Whitespace <a href="#s4.6.1-vertical-whitespace"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>A single blank line appears:</p><ol><li><em>Between</em> consecutive members (or initializers) of a class: fields, constructors,
|
||||||
|
methods, nested classes, static initializers, instance initializers.
|
||||||
|
<ul><li><span class="exception"><b>Exception:</b> a blank line between two consecutive fields (having no other code
|
||||||
|
between them) is optional. Such blank lines are used as needed to create <em>logical
|
||||||
|
groupings</em> of fields.</span></li></ul></li><li>Within method bodies, as needed to create <em>logical groupings</em> of statements.</li><li><em>Optionally</em> before the first member or after the last member of the class (neither
|
||||||
|
encouraged nor discouraged).</li><li>As required by other sections of this document (such as Section 3.3,
|
||||||
|
<a href="#s3.3-import-statements">Import statements</a>).</li></ol><p><em>Multiple</em> consecutive blank lines are permitted, but never required (or encouraged).</p><a name="s4.6.2-horizontal-whitespace"/>
|
||||||
|
<h4>4.6.2 Horizontal whitespace <a href="#s4.6.2-horizontal-whitespace"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Beyond where required by the language or other style rules, and apart from literals, comments and
|
||||||
|
Javadoc, a single ASCII space also appears in the following places <strong>only</strong>.</p><ol><li>Separating any reserved word, such as
|
||||||
|
<code class="prettyprint lang-java">if</code>,
|
||||||
|
<code class="prettyprint lang-java">for</code> or
|
||||||
|
<code class="prettyprint lang-java">catch</code>, from an open parenthesis
|
||||||
|
(<code class="prettyprint lang-java">(</code>)
|
||||||
|
that follows it on that line</li><li>Separating any reserved word, such as
|
||||||
|
<code class="prettyprint lang-java">else</code> or
|
||||||
|
<code class="prettyprint lang-java">catch</code>, from a closing curly brace
|
||||||
|
(<code class="prettyprint lang-java">}</code>) that precedes it on that line</li><li>Before any open curly brace
|
||||||
|
(<code class="prettyprint lang-java">{</code>), with two exceptions:
|
||||||
|
<ul><li><code class="prettyprint lang-java">@SomeAnnotation({a, b})</code> (no space is used)</li><li><code class="prettyprint lang-java">String[][] x = {{"foo"}};</code> (no space is required
|
||||||
|
between <code class="prettyprint lang-java">{{</code>, by item 8 below)</li></ul></li><li>On both sides of any binary or ternary operator. This also applies to the following
|
||||||
|
"operator-like" symbols:
|
||||||
|
<ul><li>the ampersand in a conjunctive type bound:
|
||||||
|
<code class="prettyprint lang-java"><T extends Foo & Bar></code></li><li>the pipe for a catch block that handles multiple exceptions:
|
||||||
|
<code class="prettyprint lang-java">catch (FooException | BarException e)</code></li><li>the colon (<code class="prettyprint lang-java">:</code>) in an enhanced
|
||||||
|
<code class="prettyprint lang-java">for</code> ("foreach") statement</li></ul></li><li>After <code class="prettyprint lang-java">,:;</code> or the closing parenthesis
|
||||||
|
(<code class="prettyprint lang-java">)</code>) of a cast</li><li>On both sides of the double slash (<code class="prettyprint lang-java">//</code>) that
|
||||||
|
begins an end-of-line comment. Here, multiple spaces are allowed, but not required.</li><li>Between the type and variable of a declaration:
|
||||||
|
<code class="prettyprint lang-java">List<String> list</code></li><li><em>Optional</em> just inside both braces of an array initializer
|
||||||
|
<ul><li><code class="prettyprint lang-java">new int[] {5, 6}</code> and
|
||||||
|
<code class="prettyprint lang-java">new int[] { 5, 6 }</code> are both valid</li></ul></li></ol><p class="note"><b>Note:</b> this rule never requires or forbids additional space at the start or end of a
|
||||||
|
line, only <em>interior</em> space.</p><a name="s4.6.3-horizontal-alignment"/>
|
||||||
|
<h4>4.6.3 Horizontal alignment: never required <a href="#s4.6.3-horizontal-alignment"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p class="terminology"><b>Terminology Note:</b> Horizontal alignment is the practice of adding a variable number of
|
||||||
|
additional spaces in your code with the goal of making certain tokens appear directly below certain
|
||||||
|
other tokens on previous lines.</p><p>This practice is permitted, but is <strong>never required</strong> by Google Style. It is not
|
||||||
|
even required to <em>maintain</em> horizontal alignment in places where it was already used.</p><p>Here is an example without alignment, then using alignment:</p><pre class="prettyprint lang-java">
|
||||||
|
private int x; // this is fine
|
||||||
|
private Color color; // this too
|
||||||
|
|
||||||
|
private int x; // permitted, but future edits
|
||||||
|
private Color color; // may leave it unaligned
|
||||||
|
</pre><p class="tip"><b>Tip:</b> Alignment can aid readability, but it creates problems for future maintenance.
|
||||||
|
Consider a future change that needs to touch just one line. This change may leave the
|
||||||
|
formerly-pleasing formatting mangled, and that is <strong>allowed</strong>. More often it prompts
|
||||||
|
the coder (perhaps you) to adjust whitespace on nearby lines as well, possibly triggering a
|
||||||
|
cascading series of reformattings. That one-line change now has a "blast radius." This can at worst
|
||||||
|
result in pointless busywork, but at best it still corrupts version history information, slows down
|
||||||
|
reviewers and exacerbates merge conflicts.</p><a name="parentheses"/><a name="s4.7-grouping-parentheses"/>
|
||||||
|
<h3>4.7 Grouping parentheses: recommended <a href="#s4.7-grouping-parentheses"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>Optional grouping parentheses are omitted only when author and reviewer agree that there is no
|
||||||
|
reasonable chance the code will be misinterpreted without them, nor would they have made the code
|
||||||
|
easier to read. It is <em>not</em> reasonable to assume that every reader has the entire Java
|
||||||
|
operator precedence table memorized.</p><a name="s4.8-specific-constructs"/>
|
||||||
|
<h3>4.8 Specific constructs <a href="#s4.8-specific-constructs"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<a name="s4.8.1-enum-classes"/>
|
||||||
|
<h4>4.8.1 Enum classes <a href="#s4.8.1-enum-classes"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>After each comma that follows an enum constant, a line-break is optional.</p><p>An enum class with no methods and no documentation on its constants may optionally be formatted
|
||||||
|
as if it were an array initializer:</p><pre class="prettyprint lang-java">
|
||||||
|
private enum Suit { CLUBS, HEARTS, SPADES, DIAMONDS }
|
||||||
|
</pre><p>Since enum classes <em>are classes</em>, all other rules for formatting classes apply.</p><a name="localvariables"/><a name="s4.8.2-variable-declarations"/>
|
||||||
|
<h4>4.8.2 Variable declarations <a href="#s4.8.2-variable-declarations"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<a name="s4.8.2.1-variables-per-declaration"/>
|
||||||
|
<h5>4.8.2.1 One variable per declaration <a href="#s4.8.2.1-variables-per-declaration"><img height="21" width="21" src="javaguidelink.png"/></a></h5>
|
||||||
|
<p>Combined declarations such as <code class="prettyprint lang-java badcode">int a, b;</code> are
|
||||||
|
<strong>not</strong> used.</p><a name="s4.8.2.2-variables-limited-scope"/>
|
||||||
|
<h5>4.8.2.2 Declared when needed, initialized as soon as
|
||||||
|
possible <a href="#s4.8.2.2-variables-limited-scope"><img height="21" width="21" src="javaguidelink.png"/></a></h5>
|
||||||
|
<p>Local variables are <strong>not</strong> habitually declared at the start of their containing
|
||||||
|
block or block-like construct. Instead, local variables are declared close to the point they are
|
||||||
|
first used (within reason), to minimize their scope. Local variable declarations typically have
|
||||||
|
initializers, or are initialized immediately after declaration.</p><a name="s4.8.3-arrays"/>
|
||||||
|
<h4>4.8.3 Arrays <a href="#s4.8.3-arrays"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<a name="s4.8.3.1-array-initializers"/>
|
||||||
|
<h5>4.8.3.1 Array initializers: can be "block-like" <a href="#s4.8.3.1-array-initializers"><img height="21" width="21" src="javaguidelink.png"/></a></h5>
|
||||||
|
<p>Any array initializer may <em>optionally</em> be formatted as if it were a "block-like
|
||||||
|
construct." For example, the following are all valid (<strong>not</strong> an exhaustive
|
||||||
|
list):</p><pre class="prettyprint lang-java">
|
||||||
|
new int[] { new int[] {
|
||||||
|
0, 1, 2, 3 0,
|
||||||
|
} 1,
|
||||||
|
2,
|
||||||
|
new int[] { 3,
|
||||||
|
0, 1, }
|
||||||
|
2, 3
|
||||||
|
} new int[]
|
||||||
|
{0, 1, 2, 3}
|
||||||
|
</pre><a name="s4.8.3.2-array-declarations"/>
|
||||||
|
<h5>4.8.3.2 No C-style array declarations <a href="#s4.8.3.2-array-declarations"><img height="21" width="21" src="javaguidelink.png"/></a></h5>
|
||||||
|
<p>The square brackets form a part of the <em>type</em>, not the variable:
|
||||||
|
<code class="prettyprint lang-java">String[] args</code>, not
|
||||||
|
<code class="prettyprint lang-java badcode">String args[]</code>.</p><a name="s4.8.4-switch"/>
|
||||||
|
<h4>4.8.4 Switch statements <a href="#s4.8.4-switch"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p class="terminology"><b>Terminology Note:</b> Inside the braces of a <em>switch block</em> are one or more
|
||||||
|
<em>statement groups</em>. Each statement group consists of one or more <em>switch labels</em>
|
||||||
|
(either <code class="prettyprint lang-java">case FOO:</code> or
|
||||||
|
<code class="prettyprint lang-java">default:</code>), followed by one or more statements.</p><a name="s4.8.4.1-switch-indentation"/>
|
||||||
|
<h5>4.8.4.1 Indentation <a href="#s4.8.4.1-switch-indentation"><img height="21" width="21" src="javaguidelink.png"/></a></h5>
|
||||||
|
<p>As with any other block, the contents of a switch block are indented +2.</p><p>After a switch label, a newline appears, and the indentation level is increased +2, exactly as
|
||||||
|
if a block were being opened. The following switch label returns to the previous indentation
|
||||||
|
level, as if a block had been closed.</p><a name="fallthrough"/><a name="s4.8.4.2-switch-fall-through"/>
|
||||||
|
<h5>4.8.4.2 Fall-through: commented <a href="#s4.8.4.2-switch-fall-through"><img height="21" width="21" src="javaguidelink.png"/></a></h5>
|
||||||
|
<p>Within a switch block, each statement group either terminates abruptly (with a
|
||||||
|
<code class="prettyprint lang-java">break</code>,
|
||||||
|
<code class="prettyprint lang-java">continue</code>,
|
||||||
|
<code class="prettyprint lang-java">return</code> or thrown exception), or is marked with a comment
|
||||||
|
to indicate that execution will or <em>might</em> continue into the next statement group. Any
|
||||||
|
comment that communicates the idea of fall-through is sufficient (typically
|
||||||
|
<code class="prettyprint lang-java">// fall through</code>). This special comment is not required in
|
||||||
|
the last statement group of the switch block. Example:</p><pre class="prettyprint lang-java">
|
||||||
|
switch (input) {
|
||||||
|
case 1:
|
||||||
|
case 2:
|
||||||
|
prepareOneOrTwo();
|
||||||
|
// fall through
|
||||||
|
case 3:
|
||||||
|
handleOneTwoOrThree();
|
||||||
|
break;
|
||||||
|
default:
|
||||||
|
handleLargeNumber(input);
|
||||||
|
}
|
||||||
|
</pre><a name="s4.8.4.3-switch-default"/>
|
||||||
|
<h5>4.8.4.3 The default case is present <a href="#s4.8.4.3-switch-default"><img height="21" width="21" src="javaguidelink.png"/></a></h5>
|
||||||
|
<p>Each switch statement includes a <code class="prettyprint lang-java">default</code> statement
|
||||||
|
group, even if it contains no code.</p><a name="annotations"/><a name="s4.8.5-annotations"/>
|
||||||
|
<h4>4.8.5 Annotations <a href="#s4.8.5-annotations"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Annotations applying to a class, method or constructor appear immediately after the
|
||||||
|
documentation block, and each annotation is listed on a line of its own (that is, one annotation
|
||||||
|
per line). These line breaks do not constitute line-wrapping (Section
|
||||||
|
4.5, <a href="#s4.5-line-wrapping">Line-wrapping</a>), so the indentation level is not
|
||||||
|
increased. Example:</p><pre class="prettyprint lang-java">
|
||||||
|
@Override
|
||||||
|
@Nullable
|
||||||
|
public String getNameIfPresent() { ... }
|
||||||
|
</pre><p class="exception"><b>Exception:</b> a <em>single</em> parameterless annotation <em>may</em> instead appear
|
||||||
|
together with the first line of the signature, for example:</p><pre class="prettyprint lang-java">
|
||||||
|
@Override public int hashCode() { ... }
|
||||||
|
</pre><p>Annotations applying to a field also appear immediately after the documentation block, but in
|
||||||
|
this case, <em>multiple</em> annotations (possibly parameterized) may be listed on the same line;
|
||||||
|
for example:</p><pre class="prettyprint lang-java">
|
||||||
|
@Partial @Mock DataLoader loader;
|
||||||
|
</pre><p>There are no specific rules for formatting parameter and local variable annotations.</p><a name="comments"/><a name="s4.8.6-comments"/>
|
||||||
|
<h4>4.8.6 Comments <a href="#s4.8.6-comments"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<a name="s4.8.6.1-block-comment-style"/>
|
||||||
|
<h5>4.8.6.1 Block comment style <a href="#s4.8.6.1-block-comment-style"><img height="21" width="21" src="javaguidelink.png"/></a></h5>
|
||||||
|
<p>Block comments are indented at the same level as the surrounding code. They may be in
|
||||||
|
<code class="prettyprint lang-java">/* ... */</code> style or
|
||||||
|
<code class="prettyprint lang-java">// ...</code> style. For multi-line
|
||||||
|
<code class="prettyprint lang-java">/* ... */</code> comments, subsequent lines must start with
|
||||||
|
<code>*</code> aligned with the <code>*</code> on the previous line.</p><pre class="prettyprint lang-java">
|
||||||
|
/*
|
||||||
|
* This is // And so /* Or you can
|
||||||
|
* okay. // is this. * even do this. */
|
||||||
|
*/
|
||||||
|
</pre><p>Comments are not enclosed in boxes drawn with asterisks or other characters.</p><p class="tip"><b>Tip:</b> When writing multi-line comments, use the
|
||||||
|
<code class="prettyprint lang-java">/* ... */</code> style if you want automatic code formatters to
|
||||||
|
re-wrap the lines when necessary (paragraph-style). Most formatters don't re-wrap lines in
|
||||||
|
<code class="prettyprint lang-java">// ...</code> style comment blocks.</p><a name="modifiers"/><a name="s4.8.7-modifiers"/>
|
||||||
|
<h4>4.8.7 Modifiers <a href="#s4.8.7-modifiers"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Class and member modifiers, when present, appear in the order
|
||||||
|
recommended by the Java Language Specification:
|
||||||
|
</p><pre>
|
||||||
|
public protected private abstract static final transient volatile synchronized native strictfp
|
||||||
|
</pre><a name="naming"/><a name="s5-naming"/>
|
||||||
|
<h2>5 Naming <a href="#s5-naming"><img height="21" width="21" src="javaguidelink.png"/></a></h2>
|
||||||
|
<a name="s5.1-identifier-names"/>
|
||||||
|
<h3>5.1 Rules common to all identifiers <a href="#s5.1-identifier-names"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>Identifiers use only ASCII letters and digits, and in two cases noted below, underscores. Thus
|
||||||
|
each valid identifier name is matched by the regular expression <code>\w+</code> .</p><p> In Google Style special prefixes or
|
||||||
|
suffixes, like those seen in the examples <code class="prettyprint lang-java badcode">name_</code>,
|
||||||
|
<code class="prettyprint lang-java badcode">mName</code>,
|
||||||
|
<code class="prettyprint lang-java badcode">s_name</code> and
|
||||||
|
<code class="prettyprint lang-java badcode">kName</code>, are <strong>not</strong> used.</p><a name="s5.2-specific-identifier-names"/>
|
||||||
|
<h3>5.2 Rules by identifier type <a href="#s5.2-specific-identifier-names"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<a name="s5.2.1-package-names"/>
|
||||||
|
<h4>5.2.1 Package names <a href="#s5.2.1-package-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Package names are all lowercase, with consecutive words simply concatenated together (no
|
||||||
|
underscores).</p><a name="s5.2.2-class-names"/>
|
||||||
|
<h4>5.2.2 Class names <a href="#s5.2.2-class-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Class names are written in <a href="#s5.3-camel-case">UpperCamelCase</a>.</p><p>Class names are typically nouns or noun phrases. Interface names may sometimes be adjectives or
|
||||||
|
adjective phrases instead. There are no specific rules or even well-established conventions for
|
||||||
|
naming annotation types.</p><p><em>Test</em> classes are named starting with the name of the class they are testing, and ending
|
||||||
|
with <code class="prettyprint lang-java">Test</code>. For example,
|
||||||
|
<code class="prettyprint lang-java">HashTest</code> or
|
||||||
|
<code class="prettyprint lang-java">HashIntegrationTest</code>.</p><a name="s5.2.3-method-names"/>
|
||||||
|
<h4>5.2.3 Method names <a href="#s5.2.3-method-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Method names are written in <a href="#s5.3-camel-case">lowerCamelCase</a>.</p><p>Method names are typically verbs or verb phrases.</p><p>Underscores may appear in JUnit <em>test</em> method names to separate logical components of the
|
||||||
|
name. One typical pattern is <code>test<i><MethodUnderTest></i>_<i><state></i></code>,
|
||||||
|
for example <code class="prettyprint lang-java">testPop_emptyStack</code>. There is no One Correct
|
||||||
|
Way to name test methods.</p><a name="constants"/><a name="s5.2.4-constant-names"/>
|
||||||
|
<h4>5.2.4 Constant names <a href="#s5.2.4-constant-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Constant names use <code class="prettyprint lang-java">CONSTANT_CASE</code>: all uppercase
|
||||||
|
letters, with words separated by underscores. But what <em>is</em> a constant, exactly?</p><p>Every constant is a static final field, but not all static final fields are constants. Before
|
||||||
|
choosing constant case, consider whether the field really <em>feels like</em> a constant. For
|
||||||
|
example, if any of that instance's observable state can change, it is almost certainly not a
|
||||||
|
constant. Merely <em>intending</em> to never mutate the object is generally not
|
||||||
|
enough. Examples:</p><pre class="prettyprint lang-java">
|
||||||
|
// Constants
|
||||||
|
static final int NUMBER = 5;
|
||||||
|
static final ImmutableList<String> NAMES = ImmutableList.of("Ed", "Ann");
|
||||||
|
static final Joiner COMMA_JOINER = Joiner.on(','); // because Joiner is immutable
|
||||||
|
static final SomeMutableType[] EMPTY_ARRAY = {};
|
||||||
|
enum SomeEnum { ENUM_CONSTANT }
|
||||||
|
|
||||||
|
// Not constants
|
||||||
|
static String nonFinal = "non-final";
|
||||||
|
final String nonStatic = "non-static";
|
||||||
|
static final Set<String> mutableCollection = new HashSet<String>();
|
||||||
|
static final ImmutableSet<SomeMutableType> mutableElements = ImmutableSet.of(mutable);
|
||||||
|
static final Logger logger = Logger.getLogger(MyClass.getName());
|
||||||
|
static final String[] nonEmptyArray = {"these", "can", "change"};
|
||||||
|
</pre><p>These names are typically nouns or noun phrases.</p><a name="s5.2.5-non-constant-field-names"/>
|
||||||
|
<h4>5.2.5 Non-constant field names <a href="#s5.2.5-non-constant-field-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Non-constant field names (static or otherwise) are written
|
||||||
|
in <a href="#s5.3-camel-case">lowerCamelCase</a>.</p><p>These names are typically nouns or noun phrases.</p><a name="s5.2.6-parameter-names"/>
|
||||||
|
<h4>5.2.6 Parameter names <a href="#s5.2.6-parameter-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Parameter names are written in <a href="#s5.3-camel-case">lowerCamelCase</a>.</p><p>One-character parameter names should be avoided.</p><a name="s5.2.7-local-variable-names"/>
|
||||||
|
<h4>5.2.7 Local variable names <a href="#s5.2.7-local-variable-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Local variable names are written in <a href="#s5.3-camel-case">lowerCamelCase</a>, and can be
|
||||||
|
abbreviated more liberally than other types of names.</p><p>However, one-character names should be avoided, except for temporary and looping variables.</p><p>Even when final and immutable, local variables are not considered to be constants, and should not
|
||||||
|
be styled as constants.</p><a name="s5.2.8-type-variable-names"/>
|
||||||
|
<h4>5.2.8 Type variable names <a href="#s5.2.8-type-variable-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Each type variable is named in one of two styles:</p><ul><li>A single capital letter, optionally followed by a single numeral (such as
|
||||||
|
<code class="prettyprint lang-java">E</code>, <code class="prettyprint lang-java">T</code>,
|
||||||
|
<code class="prettyprint lang-java">X</code>, <code class="prettyprint lang-java">T2</code>)
|
||||||
|
</li><li>A name in the form used for classes (see Section 5.2.2,
|
||||||
|
<a href="#s5.2.2-class-names">Class names</a>), followed by the capital letter
|
||||||
|
<code class="prettyprint lang-java">T</code> (examples:
|
||||||
|
<code class="prettyprint lang-java">RequestT</code>,
|
||||||
|
<code class="prettyprint lang-java">FooBarT</code>).</li></ul><a name="acronyms"/><a name="camelcase"/><a name="s5.3-camel-case"/>
|
||||||
|
<h3>5.3 Camel case: defined <a href="#s5.3-camel-case"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>Sometimes there is more than one reasonable way to convert an English phrase into camel case,
|
||||||
|
such as when acronyms or unusual constructs like "IPv6" or "iOS" are present. To improve
|
||||||
|
predictability, Google Style specifies the following (nearly) deterministic scheme.</p><p>Beginning with the prose form of the name:</p><ol><li>Convert the phrase to plain ASCII and remove any apostrophes. For example, "Müller's
|
||||||
|
algorithm" might become "Muellers algorithm".</li><li>Divide this result into words, splitting on spaces and any remaining punctuation (typically
|
||||||
|
hyphens).
|
||||||
|
|
||||||
|
<ul><li><em>Recommended:</em> if any word already has a conventional camel-case appearance in common
|
||||||
|
usage, split this into its constituent parts (e.g., "AdWords" becomes "ad words"). Note
|
||||||
|
that a word such as "iOS" is not really in camel case <em>per se</em>; it defies <em>any</em>
|
||||||
|
convention, so this recommendation does not apply.</li></ul></li><li>Now lowercase <em>everything</em> (including acronyms), then uppercase only the first
|
||||||
|
character of:
|
||||||
|
<ul><li>... each word, to yield <em>upper camel case</em>, or</li><li>... each word except the first, to yield <em>lower camel case</em></li></ul></li><li>Finally, join all the words into a single identifier.</li></ol><p>Note that the casing of the original words is almost entirely disregarded. Examples:</p><table><tr><th>Prose form</th><th>Correct</th><th>Incorrect</th></tr><tr><td>"XML HTTP request"</td><td><code class="prettyprint lang-java">XmlHttpRequest</code></td><td><code class="prettyprint lang-java badcode">XMLHTTPRequest</code></td></tr><tr><td>"new customer ID"</td><td><code class="prettyprint lang-java">newCustomerId</code></td><td><code class="prettyprint lang-java badcode">newCustomerID</code></td></tr><tr><td>"inner stopwatch"</td><td><code class="prettyprint lang-java">innerStopwatch</code></td><td><code class="prettyprint lang-java badcode">innerStopWatch</code></td></tr><tr><td>"supports IPv6 on iOS?"</td><td><code class="prettyprint lang-java">supportsIpv6OnIos</code></td><td><code class="prettyprint lang-java badcode">supportsIPv6OnIOS</code></td></tr><tr><td>"YouTube importer"</td><td><code class="prettyprint lang-java">YouTubeImporter</code><br/><code class="prettyprint lang-java">YoutubeImporter</code>*</td><td/></tr></table><p>*Acceptable, but not recommended.</p><p class="note"><b>Note:</b> Some words are ambiguously hyphenated in the English language: for example
|
||||||
|
"nonempty" and "non-empty" are both correct, so the method names
|
||||||
|
<code class="prettyprint lang-java">checkNonempty</code> and
|
||||||
|
<code class="prettyprint lang-java">checkNonEmpty</code> are likewise both correct.</p><a name="s6-programming-practices"/>
|
||||||
|
<h2>6 Programming Practices <a href="#s6-programming-practices"><img height="21" width="21" src="javaguidelink.png"/></a></h2>
|
||||||
|
<a name="s6.1-override-annotation"/>
|
||||||
|
<h3>6.1 @Override: always used <a href="#s6.1-override-annotation"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>The <code class="prettyprint lang-java">@Override</code> annotation is used in any context in
|
||||||
|
which it is legal.</p><a name="caughtexceptions"/><a name="s6.2-caught-exceptions"/>
|
||||||
|
<h3>6.2 Caught exceptions: not ignored <a href="#s6.2-caught-exceptions"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>Except as noted below, it is very rarely correct to do nothing in response to a caught
|
||||||
|
exception. (Typical responses are to log it, or if it is considered "impossible", rethrow it as an
|
||||||
|
<code class="prettyprint lang-java">AssertionError</code>.)</p><p>When it truly is appropriate to take no action whatsoever in a catch block, the reason this is
|
||||||
|
justified is explained in a comment.</p><pre class="prettyprint lang-java">
|
||||||
|
try {
|
||||||
|
int i = Integer.parseInt(response);
|
||||||
|
return handleNumericResponse(i);
|
||||||
|
} catch (NumberFormatException ok) {
|
||||||
|
// it's not numeric; that's fine, just continue
|
||||||
|
}
|
||||||
|
return handleTextResponse(response);
|
||||||
|
</pre><p class="exception"><b>Exception:</b> in tests, a caught exception may be ignored without comment <em>if</em> it is
|
||||||
|
named <code class="prettyprint lang-java">expected</code>. The following is a very common idiom
|
||||||
|
for ensuring that the method under test <em>does</em> throw an exception of the expected type, so
|
||||||
|
a comment is unnecessary here.</p><pre class="prettyprint lang-java">
|
||||||
|
try {
|
||||||
|
emptyStack.pop();
|
||||||
|
fail();
|
||||||
|
} catch (NoSuchElementException expected) {
|
||||||
|
}
|
||||||
|
</pre><a name="s6.3-static-members"/>
|
||||||
|
<h3>6.3 Static members: qualified using class <a href="#s6.3-static-members"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>When a reference to a static class member must be qualified, it is qualified with that class's
|
||||||
|
name, not with a reference or expression of that class's type.</p><pre class="prettyprint lang-java">
|
||||||
|
Foo aFoo = ...;
|
||||||
|
Foo.aStaticMethod(); // good
|
||||||
|
<span class="badcode">aFoo.aStaticMethod();</span> // bad
|
||||||
|
<span class="badcode">somethingThatYieldsAFoo().aStaticMethod();</span> // very bad
|
||||||
|
</pre><a name="finalizers"/><a name="s6.4-finalizers"/>
|
||||||
|
<h3>6.4 Finalizers: not used <a href="#s6.4-finalizers"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>It is <strong>extremely rare</strong> to override <code class="prettyprint lang-java">Object.finalize</code>.</p><p class="tip"><b>Tip:</b> Don't do it. If you absolutely must, first read and understand
|
||||||
|
<a href="http://books.google.com/books?isbn=8131726592"><em>Effective Java</em></a>
|
||||||
|
Item 7, "Avoid Finalizers," very carefully, and <em>then</em> don't do it.</p><a name="javadoc"/><a name="s7-javadoc"/>
|
||||||
|
<h2>7 Javadoc <a href="#s7-javadoc"><img height="21" width="21" src="javaguidelink.png"/></a></h2>
|
||||||
|
<a name="s7.1-javadoc-formatting"/>
|
||||||
|
<h3>7.1 Formatting <a href="#s7.1-javadoc-formatting"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<a name="s7.1.1-javadoc-multi-line"/>
|
||||||
|
<h4>7.1.1 General form <a href="#s7.1.1-javadoc-multi-line"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>The <em>basic</em> formatting of Javadoc blocks is as seen in this general example:</p><pre class="prettyprint lang-java">
|
||||||
|
/**
|
||||||
|
* Multiple lines of Javadoc text are written here,
|
||||||
|
* wrapped normally...
|
||||||
|
*/
|
||||||
|
public int method(String p1) { ... }
|
||||||
|
</pre><p>... or in this single-line example:</p><pre class="prettyprint lang-java">
|
||||||
|
/** An especially short bit of Javadoc. */
|
||||||
|
</pre><p>The general form is always acceptable. The single-line form may be substituted when there are no
|
||||||
|
at-clauses present, and the entirety of the Javadoc block (including comment markers) can fit on a
|
||||||
|
single line.</p><a name="s7.1.2-javadoc-paragraphs"/>
|
||||||
|
<h4>7.1.2 Paragraphs <a href="#s7.1.2-javadoc-paragraphs"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>One blank line—that is, a line containing only the aligned leading asterisk
|
||||||
|
(<code>*</code>)—appears between paragraphs, and before the group of "at-clauses" if
|
||||||
|
present. Each paragraph but the first has <code><p></code> immediately before the first word,
|
||||||
|
with no space after.</p><a name="s7.1.3-javadoc-at-clauses"/>
|
||||||
|
<h4>7.1.3 At-clauses <a href="#s7.1.3-javadoc-at-clauses"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Any of the standard "at-clauses" that are used appear in the order <code>@param</code>,
|
||||||
|
<code>@return</code>, <code>@throws</code>, <code>@deprecated</code>, and these four types never
|
||||||
|
appear with an empty description. When an at-clause doesn't fit on a single line, continuation lines
|
||||||
|
are indented four (or more) spaces from the position of the <code>@</code>.
|
||||||
|
</p><a name="s7.2-summary-fragment"/>
|
||||||
|
<h3>7.2 The summary fragment <a href="#s7.2-summary-fragment"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>The Javadoc for each class and member begins with a brief <strong>summary fragment</strong>. This
|
||||||
|
fragment is very important: it is the only part of the text that appears in certain contexts such as
|
||||||
|
class and method indexes.</p><p>This is a fragment—a noun phrase or verb phrase, not a complete sentence. It does
|
||||||
|
<strong>not</strong> begin with <code class="badcode">A {@code Foo} is a...</code>, or
|
||||||
|
<code class="badcode">This method returns...</code>, nor does it form a complete imperative sentence
|
||||||
|
like <code class="badcode">Save the record.</code>. However, the fragment is capitalized and
|
||||||
|
punctuated as if it were a complete sentence.</p><p class="tip"><b>Tip:</b> A common mistake is to write simple Javadoc in the form
|
||||||
|
<code class="prettyprint lang-java badcode">/** @return the customer ID */</code>. This is
|
||||||
|
incorrect, and should be changed to
|
||||||
|
<code class="prettyprint lang-java">/** Returns the customer ID. */</code>.</p><a name="s7.3-javadoc-where-required"/>
|
||||||
|
<h3>7.3 Where Javadoc is used <a href="#s7.3-javadoc-where-required"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
|
||||||
|
<p>At the <em>minimum</em>, Javadoc is present for every
|
||||||
|
<code class="prettyprint lang-java">public</code> class, and every
|
||||||
|
<code class="prettyprint lang-java">public</code> or
|
||||||
|
<code class="prettyprint lang-java">protected</code> member of such a class, with a few exceptions
|
||||||
|
noted below.</p><a name="s7.3.1-javadoc-exception-self-explanatory"/>
|
||||||
|
<h4>7.3.1 Exception: self-explanatory methods <a href="#s7.3.1-javadoc-exception-self-explanatory"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Javadoc is optional for "simple, obvious" methods like
|
||||||
|
<code class="prettyprint lang-java">getFoo</code>, in cases where there <em>really and truly</em> is
|
||||||
|
nothing else worthwhile to say but "Returns the foo".</p><p>The test methods of a unit test class are perhaps the most common example of this exemption.
|
||||||
|
These methods can <em>usually</em> be named descriptively enough that no additional documentation is
|
||||||
|
needed.</p><p class="tip"><b>Tip:</b> <strong>Important:</strong> it is not appropriate to cite this exception to justify
|
||||||
|
omitting relevant information that a typical reader might need to know. For example, for a method
|
||||||
|
named <code class="prettyprint lang-java">getCanonicalName</code>, don't omit its documentation
|
||||||
|
(with the rationale that it would say only <code class="prettyprint lang-java badcode">/** Returns
|
||||||
|
the canonical name. */</code>) if a typical reader may have no idea what the term "canonical name"
|
||||||
|
means!</p><a name="s7.3.2-javadoc-exception-overrides"/>
|
||||||
|
<h4>7.3.2 Exception: overrides <a href="#s7.3.2-javadoc-exception-overrides"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Javadoc is not always present on a method that overrides a supertype method.
|
||||||
|
</p><a name="s7.3.3-javadoc-optional"/>
|
||||||
|
<h4>7.3.3 Optional javadoc <a href="#s7.3.3-javadoc-optional"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
|
||||||
|
<p>Classes and members that are not visible outside their package still have Javadoc <em>as
|
||||||
|
needed</em>. Whenever an implementation comment would be used to define the overall purpose or
|
||||||
|
behavior of a class, method or field, that comment is written as Javadoc instead. (It's more
|
||||||
|
uniform, and more tool-friendly.)</p></div></div> <hr/>
|
||||||
|
<div class="change">Last changed: December 17, 2013</div>
|
||||||
|
</body>
|
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|
</html>
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Reference in New Issue
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