Java数据结构：循环队列的简单实现

ADT 介绍

1.数据结构

动画演示：

Tips：

• front 索引始终指向队头元素，而 tail 索引始终指向队尾元素后的空间
• 队列真实容量为 data.length-1
• 队头和队尾再数组中的真实位置为：索引值取模运算结果，模为数组的长度，即data.length

2.操作集合

• getSize() ：获得队列中的元素个数；return类型为int
• getCapacity() ：获得队列的容量；return类型为int
• isEmpty() ：判断队列是否为空；若空，return true，否则，return false
• enqueue(E element) ：入队操作
• dequeue() ：出队操作
• getFront() ：获取队头元素

代码实现

1. Queue.interface

public interface Queue<E> {
	int getSize();
	boolean isEmpty();
	void enqueue(E element);
	E dequeue();
	E getFront();
}

2. LoopQueue.java

public class LoopQueue<E> implements Queue<E> {
	final static int DEFAULTCAPACITY = 10;
	private E[] data;
	private int front, tail;
	private int size;
	public LoopQueue() {
		size = 0;
		front = 0;
		tail = 0;
		ensureCapacity(DEFAULTCAPACITY);
	}
	@Override
	public int getSize() {
		return size;
	}
	@Override
	public boolean isEmpty() {
		return front % data.length == tail % data.length;
	}
	
	public int getCapacity() {
		return data.length - 1;
	}
	
	@Override
	public void enqueue(E element) {
		if(size == getCapacity()) 
			ensureCapacity(data.length * 2);
		data[tail % data.length] = element;
		tail++;
		size++;
	}

	@Override
	public E dequeue() {
		if(isEmpty())
			throw new IllegalArgumentException("队列为空");
		if(size == getCapacity() / 2)
			ensureCapacity(data.length / 2);
		E ret = data[front % data.length];
		front++;
		size--;
		return ret;
	}

	private void ensureCapacity(int newCapacity) {
		if(newCapacity < size)
			return;
		E[] old = data;
		data = (E[])new Object[newCapacity];
		int fro = front;
		while(fro % data.length != tail % data.length) {
			data[fro % data.length] = old[fro % data.length];
			fro++;
		}
	}	
	
	@Override
	public E getFront() {
		return data[front % data.length];
	}
	
	@Override
	public String toString() {
		String s;
		StringBuilder str = new StringBuilder();
		str.append("loopQueue:"+"size:"+size+"\tCapacity:"+getCapacity()+'\n');
		str.append("front[");
		int fro = front;
		while(fro % data.length != tail % data.length) {
			str.append(data[fro % data.length]);
			if(fro % data.length != (tail - 1) % data.length)
				str.append(',');
			fro++;
		}
		str.append("]tail");
		s = str.toString();
		return s;
	}

}