设计模式-行为型模式-迭代器模式 Iterator

用于容器和容器遍历；容器可以是数组，列表，集合 或者其他的容器型数据结构

迭代器模式提供一种顺序遍历聚合对象元素而不暴露其内部实现方式的方法；

• Container/Aggregate ： 容器类接口
• ConcreteContainer/ConcreteAggregate ：具体容器类的实现类，暴露方法创建迭代器
• Iterator：迭代器接口，具有通用方法，hasNext();next()
• ConcreteIterator：一般容器内部会实现自己的迭代器，基于Iterator 接口

Java 版本中的java.util.Collection 和 java.util.Iterator 接口

//Container/Aggregate ： 容器类接口
interface ICollection extends IIterable {

	void add(E e);

	E get(int index);

}

//Iterator：迭代器接口
interface IIterator {

	boolean hasNext();

	E next();

}

//这个接口 用于每个集合的实现类都用方法返回一个迭代器
interface IIterable {

	IIterator iterator();
}

// ConcreteContainer/ConcreteAggregate ：具体容器类的实现类，暴露方法创建迭代器
class IArrayList implements ICollection {

	private Object[] elements;
	private int eIndex = 0;

	public IArrayList() {
		this.elements = new Object[5];
	}

	@Override
	public void add(E e) {
		if (eIndex == (elements.length)) {
			Object[] elementsNew = new Object[elements.length + (elements.length >> 1)];
			System.arraycopy(elements, 0, elementsNew, 0, elements.length);
			elements = elementsNew;
		}
		elements[eIndex] = e;
		eIndex++;
	}

	@Override
	public E get(int index) {
		return (E) elements[index];
	}
//暴露方法创建迭代器
	@Override
	public IIterator iterator() {
		return new IArrayListIterator();
	}
//ConcreteIterator：一般容器内部会实现自己的迭代器，基于Iterator 接口
	class IArrayListIterator implements IIterator {

		private int eachIndex = 0;

		@Override
		public boolean hasNext() {
			return eachIndex < eIndex;
		}

		@Override
		public E next() {
			E element = (E) elements[eachIndex];
			eachIndex++;
			return element;
		}
	}
}

 ConcreteContainer/ConcreteAggregate ：具体容器类的实现类，暴露方法创建迭代器
class ILinkedList implements ICollection {

	private Node head;
	private Node tail;
	int size = 0;

	@Override
	public void add(E e) {

		Node node = new Node<>();
		node.e = e;
		if (size == 0) {
			head = node;
		} else {
			node.pre = tail;
			tail.next = node;
		}
		tail = node;
		size++;
	}

	@Override
	public E get(int index) {
		if (index == 0) {
			return head.e;
		}
		Node node = head;
		for (int i = 0; i < index; i++) {
			node = node.next;
		}
		return node.e;
	}
//暴露方法创建迭代器
	@Override
	public IIterator iterator() {
		return new ILinkedListIterator();
	}
//ConcreteIterator：一般容器内部会实现自己的迭代器，基于Iterator 接口
	class ILinkedListIterator implements IIterator {

		private int eachIndex = 0;

		@Override
		public boolean hasNext() {
			return eachIndex < size;
		}

		@Override
		public E next() {
			if (eachIndex == 0) {
				eachIndex++;
				return head.e;
			}
			Node node = head;
			for (int i = 0; i < eachIndex; i++) {
				node = node.next;
			}
			eachIndex++;
			return node.e;
		}
	}

	class Node {
		public Node next;
		public Node pre;
		public E e;
	}
}

	public static void main(String[] args) {

		ICollection collection = new IArrayList<>();
		ICollection collection2 = new ILinkedList<>();
        //填充数据
		for (int i = 0; i < 10; i++) {
			collection.add(i + 100);
			collection2.add(i * 2);
		}
		//通用遍历
		for (int i = 0; i < 10; i++) {
			Integer integer = collection.get(i);
			System.out.println("collection  index value :" + integer);
		}
		for (int i = 0; i < 10; i++) {
			Integer integer = collection2.get(i);
			System.out.println("collection2  index value :" + integer);
		}

        //迭代器遍历
		IIterator iterator = collection.iterator();
		while (iterator.hasNext()) {
			Integer next = iterator.next();
			System.out.println("iterator collection  index value :" + next);
		}

		IIterator iterator2 = collection2.iterator();
		while (iterator2.hasNext()) {
			Integer next = iterator2.next();
			System.out.println("iterator2 collection  index value :" + next);
		}
	}

测试结果

collection  index value :100
collection  index value :101
collection  index value :102
collection  index value :103
collection  index value :104
collection  index value :105
collection  index value :106
collection  index value :107
collection  index value :108
collection  index value :109
collection2  index value :0
collection2  index value :2
collection2  index value :4
collection2  index value :6
collection2  index value :8
collection2  index value :10
collection2  index value :12
collection2  index value :14
collection2  index value :16
collection2  index value :18
iterator collection  index value :100
iterator collection  index value :101
iterator collection  index value :102
iterator collection  index value :103
iterator collection  index value :104
iterator collection  index value :105
iterator collection  index value :106
iterator collection  index value :107
iterator collection  index value :108
iterator collection  index value :109
iterator2 collection  index value :0
iterator2 collection  index value :2
iterator2 collection  index value :4
iterator2 collection  index value :6
iterator2 collection  index value :8
iterator2 collection  index value :10
iterator2 collection  index value :12
iterator2 collection  index value :14
iterator2 collection  index value :16
iterator2 collection  index value :18
Disconnected from the target VM, address: '127.0.0.1:51888', transport: 'socket'

Process finished with exit code 0