任何容器的底層資料結構只有兩種：一種是陣列；另一種是連結串列。例如：list,set,map,二叉樹，圖等容器。訪問容器使用Iterator迭代器。

public interface Collection_ {

    void add(Object o);
    int size();
    Iterator_ iterator();
}

public interface Iterator_ {

    boolean hasNext();
    Object next();
}


public class ArrayList_ implements Collection_{

   
 
private Object[] objects=new Object[10];
   private int currentIdex=0;
    @Override
    public void add(Object o) {
        if(currentIdex==objects.length){
            Object[] newObjects=new Object[objects.length * 2];
            System.arraycopy(objects,0,newObjects,0,objects.length);
            objects
 
=newObjects;
        }
        objects[currentIdex]=o;
        currentIdex++;
    }

    @Override
    public int size() {
        return currentIdex;
    }

    @Override
    public Iterator_ iterator() {
        return new CommenArrayList();
    }

    public class CommenArrayList implements Iterator_{

        
 
private int index=0;

        @Override
        public boolean hasNext() {
            if(index>=currentIdex){
                return false;
            }
            return  true;
        }

        @Override
        public Object next() {
            Object o=objects[index];
            index++;
            return o;
        }
    }
}

public class main {

    public static void main(String[] args) {

        Collection_ list=new ArrayList_();
        for (int i = 0; i < 15; i++) {
            list.add(new String("你好"+i));
        }
        //使用迭代器遍歷
        Iterator_ it=list.iterator();
        while (it.hasNext()){
            Object o=it.next();
            System.out.println(o);
        }
    }
}

jdk中的ArrayList也是如此設計。main方法中我們只需要更改ArrayList_,其它程式碼都不需要改變。