public interface Aggregate{
    public abstract Iterator iterator(); 
}
public interface Iterator{
    public abstract boolean hasNext();  //判断是否存在下一个元素
    public abstract Object  next();       //获取该元素
}
Aggregate创建迭代器Iterator，Iterator中保存当前Aggregate实例,hasNext判断集合Aggregate是否有下个元素，next取出这个元素并将指定指下下一个。

类适配器模式
    public interface Target{
        public abstract void printA();
    }
    public class Adaptee{
        public void showA(){
            ...
        }
    }
    public class Adapter extend Adaptee implements Target{
        public void printA(){
            showA();
        }
    }
    调用：
        Target a = new Adapter();
        a.printA();
对象适配器模式:
    public abstract class Target{
        public abstract  void printA();
    }
    public class Adaptee{
        public showA(){
            ...
        }
    }
    public class Adapter extend Target{
        Adaptee adaptee;
        public Adapter(Adaptee adaptee){
            this.adaptee = adaptee;
        }
        public void printA(){
            adaptee.showA();
        }
    }
    调用:
    Target a = new Adapter(new Adaptee());
    a.printA();