124 lines
3.5 KiB
Java
124 lines
3.5 KiB
Java
## 解释器（Interpreter）
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### Intent
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为语言创建解释器，通常由语言的语法和语法分析来定义。
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### Class Diagram
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- TerminalExpression：终结符表达式，每个终结符都需要一个 TerminalExpression。
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- Context：上下文，包含解释器之外的一些全局信息。
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/2b125bcd-1b36-43be-9b78-d90b076be549.png"/> </div><br>
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### Implementation
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以下是一个规则检验器实现，具有 and 和 or 规则，通过规则可以构建一颗解析树，用来检验一个文本是否满足解析树定义的规则。
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例如一颗解析树为 D And (A Or (B C))，文本 "D A" 满足该解析树定义的规则。
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这里的 Context 指的是 String。
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```java
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public abstract class Expression {
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public abstract boolean interpret(String str);
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}
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```
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```java
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public class TerminalExpression extends Expression {
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private String literal = null;
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public TerminalExpression(String str) {
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literal = str;
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}
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public boolean interpret(String str) {
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StringTokenizer st = new StringTokenizer(str);
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while (st.hasMoreTokens()) {
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String test = st.nextToken();
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if (test.equals(literal)) {
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return true;
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}
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}
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return false;
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}
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}
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```
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```java
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public class AndExpression extends Expression {
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private Expression expression1 = null;
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private Expression expression2 = null;
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public AndExpression(Expression expression1, Expression expression2) {
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this.expression1 = expression1;
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this.expression2 = expression2;
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}
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public boolean interpret(String str) {
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return expression1.interpret(str) && expression2.interpret(str);
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}
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}
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```
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```java
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public class OrExpression extends Expression {
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private Expression expression1 = null;
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private Expression expression2 = null;
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public OrExpression(Expression expression1, Expression expression2) {
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this.expression1 = expression1;
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this.expression2 = expression2;
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}
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public boolean interpret(String str) {
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return expression1.interpret(str) || expression2.interpret(str);
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}
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}
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```
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```java
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public class Client {
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/**
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* 构建解析树
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*/
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public static Expression buildInterpreterTree() {
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// Literal
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Expression terminal1 = new TerminalExpression("A");
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Expression terminal2 = new TerminalExpression("B");
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Expression terminal3 = new TerminalExpression("C");
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Expression terminal4 = new TerminalExpression("D");
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// B C
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Expression alternation1 = new OrExpression(terminal2, terminal3);
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// A Or (B C)
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Expression alternation2 = new OrExpression(terminal1, alternation1);
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// D And (A Or (B C))
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return new AndExpression(terminal4, alternation2);
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}
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public static void main(String[] args) {
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Expression define = buildInterpreterTree();
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String context1 = "D A";
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String context2 = "A B";
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System.out.println(define.interpret(context1));
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System.out.println(define.interpret(context2));
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}
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}
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```
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```html
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true
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false
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```
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### JDK
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- [java.util.Pattern](http://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html)
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- [java.text.Normalizer](http://docs.oracle.com/javase/8/docs/api/java/text/Normalizer.html)
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- All subclasses of [java.text.Format](http://docs.oracle.com/javase/8/docs/api/java/text/Format.html)
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- [javax.el.ELResolver](http://docs.oracle.com/javaee/7/api/javax/el/ELResolver.html)
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