就是Iterator 遍歷用

interface Iterator{
    public Object next();
    public boolean hasNext();
}
class ConcreteIterator implements Iterator{
    private List list = new ArrayList();
    private int cusor =0;
    public ConcreteIterator(List list){
        this.list=list;
    }
    public boolean hasNext(){
        if(cusor == list.size()){
            return false;
        }
        return true;
    }
    public Object next(){
        Object obj =null;
        if(this.hasNext()){
            obj=this.list.get(cusor++);
        }
        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 IteratorTest {
    public static void main(String[] args){
        Aggregate ag = new ConcreteAggregate();
        ag.add("A");
        ag.add("B");
        ag.add("C");
        Iterator it =ag.iterator();
        while (it.hasNext()){
            String str =(String) it.next();
            System.out.println(str);
        }
    }
}