组合模式

一、定义

将对象(objects)组合成树形结构来表示“部分-整体”层次结构，使得客户端一致地对待单个对象和组合对象。

二、类图表示

三、实现

1、Component

package pattern.structual.composite;

public abstract class Component {

	protected String name;
	public Component(String name) {
		this.name = name;
	}
	
	public void display(int depth){
		StringBuilder sb = new StringBuilder();
		for(int i = 0; i < depth; i++){
			sb.append(" ");
		}
		System.out.println(String.format("%s--%s", sb, name));
	}
	@Override
	public String toString() {
		return String.format("Type: %s  Name: %s", this.getClass().getSimpleName(), name);
	}
	public abstract void add(Component component);
	public abstract void remove(Component component);
	public abstract Component getChild(int index);
}

2、Leaf

package pattern.structual.composite;

public class Leaf extends Component {

	public Leaf(String name) {
		super(name);
	}

	@Override
	public void add(Component component) {
		System.out.println("can't add to a leaf");
	}

	@Override
	public void remove(Component component) {
		System.out.println("can't remove from a leaf");
	}

	@Override
	public Component getChild(int index) {
		System.out.println("can't get child from a leaf");
		return null;
	}

	@Override
	public void display(int depth) {
		super.display(depth);
	}

}

3、Composite

package pattern.structual.composite;

import java.util.ArrayList;
import java.util.List;

public class Composite extends Component {

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

	@Override
	public void add(Component component) {
		children.add(component);
	}

	@Override
	public void remove(Component component) {
		children.remove(component);
	}

	@Override
	public Component getChild(int index) {
		return children.get(index);
	}

	@Override
	public void display(int depth) {
		super.display(depth);
		for(Component com : children){
			com.display(depth + 2);
		}
	}

}

四、使用

package pattern.structual.composite;

public class Client {

	public static void main(String[] args) {
		Component root = new Composite("Root");
		root.add(new Leaf("Leaf A"));
		root.add(new Leaf("Leaf B"));
		
		Component composite = new Composite("Composite X");
		composite.add(new Leaf("Leaf X1"));
		composite.add(new Leaf("Leaf X2"));
		root.add(composite);
		
		root.add(new Leaf("Leaf C"));
		
		root.display(0);
		
		Component child = root.getChild(2);
		System.out.println("Index-2: " + child);
		
		root.remove(child);
		root.display(0);
	}
}

• 程序输出：

五、适用场合

• 想表示对象的“部分–整体”结构时
• 想在客户端一致的使用组合对象或单个对象