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：包含有獲取迭代器的方法  */interface Container{ public Iterator iterator();}/** * 具體實(shí)現(xiàn)類 * @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; }  }}