组合模式

1. 抽象构件角色

public abstract class Component {
    public void doSomething() {
        //具体处理或逻辑
    }
    //节点添加
    public abstract void add(Component component) ;
    //节点删除
    public abstract void remove(Component component) ;
    //获取子节点
    public abstract List<Component> getChild();
}

2. 树枝节点

public class Composite extends Component {
    //整个树容器
    private List<Component> componentList = new ArrayList<>();
    //节点添加
    @Override
    public void add(Component component) {
        this.componentList.add(component);
    }
    //节点删除
    @Override
    public void remove(Component component) {
        this.componentList.remove(component);
    }
    //获取子节点
    @Override
    public List<Component> getChild() {
        return this.componentList;
    }
}

3. 叶子节点

public class Leaf extends Component {
    @Deprecated
    @Override
    public void add(Component component) {
        throw  new UnsupportedOperationException();
    }
    @Deprecated
    @Override
    public void remove(Component component) {
        throw  new UnsupportedOperationException();
    }
    @Deprecated
    @Override
    public List<Component> getChild() {
        throw  new UnsupportedOperationException();
    }
}

4. 树的创建及组装

    Component root = new Composite();
    Component composite = new Composite();
    Component leaf = new Leaf();
    root.add(composite);
    composite.add(leaf);

5. 树的遍历

    private void display(Component root) {
        for (Component component :
                root.getChild()) {
            if (component instanceof Leaf) {
                component.doSomething();
            } else {
                display(component);
            }
        }
    }