public class Demo {

 public static void main(String[] args) {
 ActualContainer container = new ActualContainer();
 for(int i = 5 ; i < 20 ; i++){
  container.add(i);
 }
 
 Iterator iterator = container.iterator();
 while(iterator.hasNext()){
  System.out.println(iterator.next());
 }
 }
}

/**
 * 迭代器接口，包含有常用的迭代器方法 
 */
interface Iterator{
 public boolean hasNext();
 
 public Object next();
}

/**
 * 容器接口：包含有获取迭代器的方法 
 */
interface Container{
 public Iterator iterator();
}

/**
 * 具体实现类
 * @author jiaoyuyu
 *
 */
class ActualContainer implements Container{

 private List<Object> list = new ArrayList<>();
 
 public void add(Object obj){
 this.list.add(obj);
 }
 
 public void remove(Object obj){
 this.list.remove(obj);
 }
 
 public Object get(int index){
 if(index <= (this.list.size() - 1)){
  return this.list.get(index);
 }
 return null;
 }
 
 
 public Iterator iterator() {
 return new ActualIterator();
 }
 
 private class ActualIterator implements Iterator{

 private int pointer = 0;
 
 public boolean hasNext() {
  return this.pointer < list.size() ? true : false;
 }

 public Object next() {
  if(this.pointer < list.size()){
  Object obj = list.get(pointer);
  pointer++;
  return obj;
  }
  return null;
 }
 
 }
}