组合模式

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组合模式(Composite),将对象组合成树形结构以表示’部分-整体’的层次结构。组合模式使得用户对单个对象和组合对象的使用具有一致性

Class Diagram

Implementation

组件接口

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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);
}

组合组件

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public class Composite extends Component{

    private List<Component> child;

    public Composite(String name) {
        super(name);
        child = new ArrayList<Component>();
    }

    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);
        }
    }

    public void add(Component component) {
        child.add(component);
    }

    public void remove(Component component) {
        child.remove(component);
    }
}

实例组件

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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();
    }
}

测试类

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public class CompositeTest {

    @Test
    public void test() throws Exception {
        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();
    }
}

Example

  • java.util.Map#putAll(Map)
  • java.util.List#addAll(Collection)
  • java.util.Set#addAll(Collection)

Refence