设计模式-Iterator模式

描述

• 定义 Iterator模式用于容器与容器遍历，可以将遍历与现实分离开，在遍历时只需调用迭代器的方法，无需关心具体容器实现类的方法

代码简单实现ArrayList

• Iterator接口定义

  public interface Iterator<E> {
  	boolean hasNext();
  	E next();
  	void remove();
  }
  

  hasNext()：用户循环终止条件 next()：放回集合中的元素、 remove()：移除集合中的元素
• List接口定义

  public interface List<E> {
  	void add(E e);
  	int size();
  	Iterator<E> iterator();
  
  }
  

• List实现类ArrayList

  public class ArrayList<E> implements List<E> {
  
  	Object[] objs;
  	private static final int DEFAULT_CAPACITY = 10;
  	private int size = 0;
  	
  	public ArrayList() {
      	objs = new Object[DEFAULT_CAPACITY];
  	}
  
  	public void add(E e) {
      	if (size >= objs.length) {
          	Object[] newObjs = new Object[objs.length + DEFAULT_CAPACITY];
          	System.arraycopy(objs, 0, newObjs, 0, objs.length);
          	objs = newObjs;
      	}
      	objs[size++] = e;
  	}
  
  	public int size() {
      	return size;
  	}
  
  	public E remove(int index) {
      	if (index >= size)
          	throw new RuntimeException("index out of bounds");
  
      	E oldValue = (E) objs[index];
  
      	int numMoved = size - index - 1;
      	if (numMoved > 0) {
          	System.arraycopy(objs, index + 1, objs, index,numMoved);
      	}
      	objs[--size] = null;
      	return oldValue;
  	}
  
  	public Iterator<E> iterator() {
      	return new ArrayIterator();
  	}
  
  	private class ArrayIterator implements Iterator {
      	int index = 0;
  
      	public boolean hasNext() {
          	if (index == size) {
              	return false;
          	}
          	return true;
      	}
  
      	public Object next() {
          	return objs[index++];
      	}
  
      	public void remove() {
          	ArrayList.this.remove(index);
      	}
  	}
  }