client.java

设计模式描述设计模式描述设计模式描述设计模式描述

/*
 * Created on 2005-5-11
 *
 意图 提供一种方法顺序访问一个聚合对象中各个元素, 而又不需暴露该对象的内部表示。 
 适用性 访问一个聚合对象的内容而无需暴露它的内部表示。 
 支持对聚合对象的多种遍历。 
 为遍历不同的聚合结构提供一个统一的接口(即, 支持多态迭代)。  
 */
package com.test.pattern.behavir.iterator;

import java.util.ArrayList;

/**
 * @author Administrator
 * 
 * TODO To change the template for this generated type comment go to Window -
 * Preferences - Java - Code Style - Code Templates
 */
class Node {
	private String name;

	public String getName() {
		return name;
	}

	public Node(String s) {
		name = s;
	}
}

class NodeCollection {
	private ArrayList list = new ArrayList();

	private int nodeMax = 0;

	// left as a student exercise - implement collection
	// functions to remove and edit entries also
	public void AddNode(Node n) {
		list.add(n);
		nodeMax++;
	}

	public Node GetNode(int i) {
		return ((Node) list.get(i));
	}

	public int getNodeMax() {
		return nodeMax;
	}
}

/*
 * The iterator needs to understand how to traverse the collection It can do
 * that as way it pleases - forward, reverse, depth-first,
 */

abstract class Iterator {
	abstract public Node Next();
}

class ReverseIterator extends Iterator {
	private NodeCollection nodeCollection;

	private int currentIndex;

	public ReverseIterator(NodeCollection c) {
		nodeCollection = c;
		currentIndex = c.getNodeMax() - 1; // array index starts at 0!
	}

	// note: as the code stands, if the collection changes,
	// the iterator needs to be restarted
	public Node Next() {
		if (currentIndex == -1)
			return null;
		else
			return (nodeCollection.GetNode(currentIndex--));
	}
}

/// <summary>
/// Summary description for Client.
/// </summary>

public class Client {
	public static void main(String[] args) {
		NodeCollection c = new NodeCollection();
		c.AddNode(new Node("first"));
		c.AddNode(new Node("second"));
		c.AddNode(new Node("third"));

		// now use iterator to traverse this
		ReverseIterator i = new ReverseIterator(c);

		// the code below will work with any iterator type
		Node n;
		do {
			n = i.Next();
			if (n != null)
				System.out.println(n.getName());
		} while (n != null);

	}
}