迭代器模式

提供一種方法順序訪問一個聚合對象中各個元素, 而又無須暴露該對象的內部表示。存儲數據和遍歷數據的職責分離，
抽象裂變類，抽象迭代器類。
迭代器接口：

interface Iterator {  
    public Object next();  
    public boolean hasNext();  
}  
class ConcreteIterator implements Iterator{  
    private List list = new ArrayList();  
    private int cursor =0;  
    public ConcreteIterator(List list){  
        this.list = list;  
    }  
    public boolean hasNext() {  
        if(cursor==list.size()){  
            return false;  
        }  
        return true;  
    }  
    public Object next() {  
        Object obj = null;  
        if(this.hasNext()){  
            obj = this.list.get(cursor++);  
        }  
        return obj;  
    }  
}  
interface Aggregate {  
    public void add(Object obj);  
    public void remove(Object obj);  
    public Iterator iterator();  
}  
class ConcreteAggregate implements Aggregate {  
    private List list = new ArrayList();  
    public void add(Object obj) {  
        list.add(obj);  
    }  

    public Iterator iterator() {  
        return new ConcreteIterator(list);  
    }  

    public void remove(Object obj) {  
        list.remove(obj);  
    }  
}  
public class Client {  
    public static void main(String[] args){  
        Aggregate ag = new ConcreteAggregate();  
        ag.add("小明");  
        ag.add("小紅");  
        ag.add("小剛");  
        Iterator it = ag.iterator();  
        while(it.hasNext()){  
            String str = (String)it.next();  
            System.out.println(str);  
        }  
    }  
}