JAVA 设计模式 迭代器模式

 interface Iterator {
 public Object first();
 public Object next();
 public boolean isDone();
 public Object currentItem();
 } 

 class ConcreteIterator implements Iterator {
 private int current = 0;
 private ConcreteAggregate aggregate;
 
 public ConcreteIterator(ConcreteAggregate aggregate) {
 this.aggregate = aggregate;
     }
 
     @Override
 public Object first() {
 return aggregate.get(0);
     }
 
     @Override
 public Object next() {
         current++;
 if (current < aggregate.size()) {
 return aggregate.get(current);
         }
 return null;
     }
 
     @Override
 public boolean isDone() {
 return (current >= aggregate.size()) ? true : false;
     }
 
     @Override
 public Object currentItem() {
 return aggregate.get(current);
     }
 } 

 interface Aggregate {
 public Iterator CreateIterator();
 } 

 class ConcreteAggregate implements Aggregate {
 private List<Object> items = new ArrayList<Object>();
 
     @Override
 public Iterator CreateIterator() {
 return new ConcreteIterator(this);
     }
 
 public int size() {
 return items.size();
     }
 
 public Object get(int index) {
 return items.get(index);
     }
 
 public void set(int index, Object element) {
         items.set(index, element);
     }
 
 public void add(Object element) {
         items.add(element);
     }
 } 

 public class IteratorPattern {
 public static void main(String[] args) {
         ConcreteAggregate aggregate = new ConcreteAggregate();
         aggregate.add("张三");
         aggregate.add("李四");
         aggregate.add("王五");
         aggregate.add("赵六");
 
         Iterator iter = new ConcreteIterator(aggregate);
         Object item = iter.first();
         System.out.println("第一个人是：" + item);
         System.out.println("所有人的名单是：");
 while (!iter.isDone()) {
             System.out.println(iter.currentItem());
             iter.next();
         }
     }
 } 

第一个人是：张三
 所有人的名单是：
 张三
 李四
 王五
 赵六