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notes/设计模式 - 组合.md

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+## 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。
+
+<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/2b8bfd57-b4d1-4a75-bfb0-bcf1fba4014a.png"/> </div><br>
+
+### Implementation
+
+```java
+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);
+}
+```
+
+```java
+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);
+    }
+}
+```
+
+```java
+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();
+    }
+}
+```
+
+```java
+public class Client {
+    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();
+    }
+}
+```
+
+```html
+Composite:root
+--left:1
+--Composite:2
+----left:21
+----Composite:22
+------left:221
+--left:3
+```
+
+### 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)
+
+
+
+
+
+
+<div align="center"><img width="320px" src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/githubio/公众号二维码-2.png"></img></div>