设计模式 - 组合
# 组合（Composite）
# Intent
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。
# Class Diagram
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。
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。
# Implementation
package com.code.structural.example7;
public abstract class Component {
protected String name;
public Component(String name) {
this.name = name;
}
public void print() {
print(0);
}
abstract void print(int level);
abstract public void add(Component component);
abstract public void remove(Component component);
}
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package com.code.structural.example7;
import java.util.ArrayList;
import java.util.List;
public class Composite extends Component {
private List<Component> child;
public Composite(String name) {
super(name);
child = new ArrayList<>();
}
@Override
void print(int level) {
for (int i = 0; i < level; i++) {
System.out.print("--");
}
System.out.println("Composite:" + name);
for (Component component : child) {
component.print(level + 1);
}
}
@Override
public void add(Component component) {
child.add(component);
}
@Override
public void remove(Component component) {
child.remove(component);
}
}
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package com.code.structural.example7;
public class Leaf extends Component {
public Leaf(String name) {
super(name);
}
@Override
void print(int level) {
for (int i = 0; i < level; i++) {
System.out.print("--");
}
System.out.println("left:" + name);
}
@Override
public void add(Component component) {
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
}
@Override
public void remove(Component component) {
throw new UnsupportedOperationException();
}
}
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package com.code.structural.example7;
public class Main {
public static void main(String[] args) {
Composite root = new Composite("root");
Component node1 = new Leaf("1");
Component node2 = new Composite("2");
Component node3 = new Leaf("3");
root.add(node1);
root.add(node2);
root.add(node3);
Component node21 = new Leaf("21");
Component node22 = new Composite("22");
node2.add(node21);
node2.add(node22);
Component node221 = new Leaf("221");
node22.add(node221);
root.print();
}
}
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Composite:root
--left:1
--Composite:2
----left:21
----Composite:22
------left:221
--left:3
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# JDK
- javax.swing.JComponent#add(Component)
- java.awt.Container#add(Component)
- java.util.Map#putAll(Map)
- java.util.List#addAll(Collection)
- java.util.Set#addAll(Collection)