package designpattern.iterator;
import java.util.Iterator;
public interface MyList<E> extends Iterable<E> {// 为了客户端直接通过接口使用foreach方法
    void set(E e, int index);
    E get(int index);
    void remove(int index);// 数组实现，有点麻烦，就不写了
 
    void changeIterator(Iterator iterator);
    int getSize();
}

package designpattern.iterator;
import java.util.Iterator;
public class MyArrayList<E> implements MyList<E>, Iterable<E> {
    E[] data;
    private int size;
    Iterator<E> iterator;
    public MyArrayList(E[] data) {
        super();
        this.data = data;
        size = data.length;
        iterator = new MyInteratorAsc<>(this);// 默认使用正序迭代器
    }
    @Override
    public void set(E e, int index) {
        if (index < size) {
            data[index] = e;
        } else {
            System.out.println(index + "大于数组大小");
        }
    }
    @Override
    public E get(int index) {
        return data[index];
    }
    @Override
    public Iterator<E> iterator() {
        return iterator;
    }
    @Override
    public void remove(int index) {
        throw new UnsupportedOperationException("暂未实现");
    }
    @Override
    public int getSize() {
        return size;
    }
    @Override
    public void changeIterator(Iterator iterator) {
        this.iterator = iterator;
    }
}

package designpattern.iterator;
import java.util.Iterator;
public class MyInteratorAsc<E> implements Iterator<E> {
    MyList<E> myList;
    public MyInteratorAsc(MyList<E> myList) {
        super();
        this.myList = myList;
        this.current = 0;
    }
    int current;
    @Override
    public boolean hasNext() {
        if (current < myList.getSize()) {
            return true;
        } else {
            return false;
        }
    }
    @Override
    public E next() {
        return myList.get(current++);
    }
}

package designpattern.iterator;
import java.util.Iterator;
public class MyInteratorDesc<E> implements Iterator<E> {
    MyList<E> myList;
    public MyInteratorDesc(MyList<E> myList) {
        super();
        this.myList = myList;
        this.current = myList.getSize() - 1;
    }
    int current;
    @Override
    public boolean hasNext() {
        if (current >= 0) {
            return true;
        } else {
            return false;
        }
    }
    @Override
    public E next() {
        return myList.get(current--);
    }
}

package designpattern.iterator;
public class Client {
    public static void main(String[] args) {
        MyList<String> myList = new MyArrayList<>(new String[4]);
        myList.set("鼠", 0);
        myList.set("牛", 1);
        myList.set("虎", 2);
        myList.set("兔", 3);
        myList.set("龙", 4);
        for (String string : myList) {
            System.out.println(string);
        }
        System.out.println("-------换成倒序-------");
        myList.changeIterator(new MyInteratorDesc<>(myList));
        for (String string : myList) {
            System.out.println(string);
        }
    }
}

4大于数组大小
鼠
牛
虎
兔
-------换成倒序-------
兔
虎
牛
鼠