134 lines
3.1 KiB
Java
134 lines
3.1 KiB
Java
## 组合（Composite）
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### Intent
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将对象组合成树形结构来表示“整体/部分”层次关系，允许用户以相同的方式处理单独对象和组合对象。
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### Class Diagram
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组件（Component）类是组合类（Composite）和叶子类（Leaf）的父类，可以把组合类看成是树的中间节点。
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组合对象拥有一个或者多个组件对象，因此组合对象的操作可以委托给组件对象去处理，而组件对象可以是另一个组合对象或者叶子对象。
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/2b8bfd57-b4d1-4a75-bfb0-bcf1fba4014a.png"/> </div><br>
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### Implementation
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```java
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public abstract class Component {
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protected String name;
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public Component(String name) {
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this.name = name;
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}
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public void print() {
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print(0);
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}
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abstract void print(int level);
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abstract public void add(Component component);
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abstract public void remove(Component component);
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}
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```
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```java
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public class Composite extends Component {
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private List<Component> child;
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public Composite(String name) {
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super(name);
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child = new ArrayList<>();
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}
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@Override
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void print(int level) {
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for (int i = 0; i < level; i++) {
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System.out.print("--");
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}
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System.out.println("Composite:" + name);
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for (Component component : child) {
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component.print(level + 1);
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}
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}
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@Override
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public void add(Component component) {
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child.add(component);
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}
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@Override
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public void remove(Component component) {
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child.remove(component);
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}
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}
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```
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```java
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public class Leaf extends Component {
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public Leaf(String name) {
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super(name);
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}
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@Override
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void print(int level) {
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for (int i = 0; i < level; i++) {
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System.out.print("--");
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}
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System.out.println("left:" + name);
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}
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@Override
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public void add(Component component) {
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throw new UnsupportedOperationException(); // 牺牲透明性换取单一职责原则，这样就不用考虑是叶子节点还是组合节点
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}
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@Override
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public void remove(Component component) {
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throw new UnsupportedOperationException();
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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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public static void main(String[] args) {
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Composite root = new Composite("root");
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Component node1 = new Leaf("1");
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Component node2 = new Composite("2");
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Component node3 = new Leaf("3");
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root.add(node1);
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root.add(node2);
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root.add(node3);
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Component node21 = new Leaf("21");
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Component node22 = new Composite("22");
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node2.add(node21);
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node2.add(node22);
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Component node221 = new Leaf("221");
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node22.add(node221);
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root.print();
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}
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}
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```
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```html
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Composite:root
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--left:1
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--Composite:2
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----left:21
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----Composite:22
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------left:221
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--left:3
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```
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### JDK
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- javax.swing.JComponent#add(Component)
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- java.awt.Container#add(Component)
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- java.util.Map#putAll(Map)
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- java.util.List#addAll(Collection)
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- java.util.Set#addAll(Collection)
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