设计模式--组合模式

   Composite模式定义:
将对象以树形结构组织起来,以达成“部分－整体” 的层次结构，使得客户端对单个对象和组合对象的使用具有一致性.

Composite比较容易理解，想到Composite就应该想到树形结构图。组合体内这些对象都有共同接口,当组合体一个对象的方法被调用执行时，Composite将遍历(Iterator)整个树形结构,寻找同样包含这个方法的对象并实现调用执行。可以用牵一动百来形容。

  Composite好处:
1.使客户端调用简单，客户端可以一致的使用组合结构或其中单个对象，用户就不必关系自己处理的是单个对象还是整个组合结构，这就简化了客户端代码。
2.更容易在组合体内加入对象部件. 客户端不必因为加入了新的对象部件而更改代码。

package composite;

public abstract class Component {

	public abstract void operation();

	public abstract void add(Component child) throws AbstractMethodError;

	public abstract void remove(Component child) throws AbstractMethodError;

	public abstract Component getChild(int index) throws AbstractMethodError;

}

package composite;

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

public class Composite extends Component {

	private final List<Component> fChildren = new ArrayList<Component>();

	public void operation() {
		Iterator<Component> iterator = fChildren.iterator();
		while (iterator.hasNext()) {
			((Component) iterator.next()).operation();
		}
	}

	public void add(Component child) throws AbstractMethodError {
		fChildren.add(child);
	}

	public void remove(Component child) throws AbstractMethodError {
		fChildren.remove(child);
	}

	public Component getChild(int index) throws AbstractMethodError {
		return (Component) fChildren.get(index);
	}

}

package composite;

/**
 * @author ZERO
 */
public class Leaf_A extends Component {

	private static final String ERROR_MSG = "This method should never be called.";

	public void operation() {
	System.out.println("Leaf_A=====TODO");
	}

	public void add(Component child) throws AbstractMethodError {
		throw new AbstractMethodError(ERROR_MSG);
	}

	public void remove(Component child) throws AbstractMethodError {
		throw new AbstractMethodError(ERROR_MSG);
	}

	public Component getChild(int index) throws AbstractMethodError {
		throw new AbstractMethodError(ERROR_MSG);
	}

}

package composite;

/**
 * @author ZERO
 */
public class Leaf_B extends Component {

	private static final String ERROR_MSG = "This method should never be called.";

	public void operation() {
		System.out.println("Leaf_B=====TODO");
	}

	public void add(Component child) throws AbstractMethodError {
		throw new AbstractMethodError(ERROR_MSG);
	}

	public void remove(Component child) throws AbstractMethodError {
		throw new AbstractMethodError(ERROR_MSG);
	}

	public Component getChild(int index) throws AbstractMethodError {
		throw new AbstractMethodError(ERROR_MSG);
	}

}

package composite;

/**
 * @author ZERO
 */
public class Leaf_C extends Component {

	private static final String ERROR_MSG = "This method should never be called.";

	public void operation() {
		System.out.println("Leaf_C=====TODO");
	}

	public void add(Component child) throws AbstractMethodError {
		throw new AbstractMethodError(ERROR_MSG);
	}

	public void remove(Component child) throws AbstractMethodError {
		throw new AbstractMethodError(ERROR_MSG);
	}

	public Component getChild(int index) throws AbstractMethodError {
		throw new AbstractMethodError(ERROR_MSG);
	}

}

package composite;

/**
 * @author ZERO
 */
public class Client {

	private Component fComponent = null;

	public Client() {
		super();
	}

	public Client(Component component) {
		super();
		fComponent = component;
	}

	public void createComposite() {
		fComponent = new Composite();

		Composite composite = new Composite();
		composite.add(new Leaf_A());
		composite.add(new Leaf_B());

		fComponent.add(composite);
		fComponent.add(new Leaf_C());
		fComponent.getChild(0).add(new Leaf_A());
		fComponent.getChild(0).add(new Leaf_A());
	}

	public void useComposite() {
		fComponent.operation();
	}

	public static void main(String[] args) {
		Client client = new Client();
		client.createComposite();
		client.useComposite();
		System.out.println("-----------");
		client.fComponent.operation();
		System.out.println("-----------");
		client.fComponent.getChild(0).operation();
		System.out.println("-----------");
		client.fComponent.getChild(1).operation();
	}

}