第二十五篇 設計模式--迭代器模式

定義：提供一種方法順序訪問一個聚合對象中各個元素，而又不需暴露該對象的內部表示。

代碼：

package iterator_model;

import java.util.ArrayList;
import java.util.List;
/**
 * 
 * @author naivor
 *		迭代器模式-場景類
 */
public class IteratorModel {
	public static void main(String[] args) {
		List<Object> list=new ArrayList<Object>();
		list.add("hello");
		list.add("小明");
		list.add("老馬");
		list.add("薯條");
		list.add("下雨");
		list.add("電腦");
		
		ConcreteAggregate aggregate=new ConcreteAggregate(list);
		ConcreteIterator iterator=new ConcreteIterator(aggregate);
		
		Object item=iterator.first();
		while(!iterator.isDone()){
			item=iterator.currentItem();
			System.out.println(item.toString());
			
			iterator.next();
		}
	}
}
/**
 * 
 * @author naivor
 *		迭代器模式-迭代器抽象類
 */
abstract class Iterator{
	 public abstract Object first();
	 public abstract Object next();
	 public abstract boolean isDone();
	 public abstract Object currentItem();
}
/**
 * 
 * @author naivor
 *		迭代器模式-聚集抽象類
 */
abstract class Aggregate{
	public abstract Iterator createIterator();
}
/**
 * 
 * @author naivor
 *		迭代器模式-聚集具體類
 */
class ConcreteAggregate extends Aggregate{
	private List<Object> items;
	
	public ConcreteAggregate(List<Object> items) {
		this.items=items;
	}
	@Override
	public Iterator createIterator() {
		// TODO Auto-generated method stub
		return new ConcreteIterator(this);
	}
	
	public int getCount(){
		return items.size();
	}
	
	public Object getItem(int index){
		return items.get(index);
	}
	
	
}
/**
 * 
 * @author naivor
 *		迭代器模式-迭代器具體類
 */
class ConcreteIterator extends Iterator{
	private ConcreteAggregate aggregate;
	private int current=0;
	
	public ConcreteIterator(ConcreteAggregate aggregate) {
		this.aggregate=aggregate;
	}

	@Override
	public Object first() {
		return aggregate.getItem(0);
	}

	@Override
	public Object next() {
		current++;
		if (current<=aggregate.getCount()) {
			return aggregate.getItem(current);
		}
		return null;
	}

	@Override
	public boolean isDone() {
		if (current>=aggregate.getCount()) {
			return true;
		}
		return false;
	}

	@Override
	public Object currentItem() {
		return aggregate.getItem(current);
	}
	
}