java数据结构队列

队列类似于现实生活中的排队。队列是先进先出的原则，只允许在队列头部去除元素，队列尾部添加元素。

下面是分别用数组和链表为存储结构实现的队列

public interface Queue<T> {
	
	int size();
	
	T remove();
	
	void add(T element);
	
	boolean isEmpty();
	
	void clear();
	
	boolean hasElement();
}

public class ArrayQueue<T> implements Queue<T>{

	//数组的默认大小
	private static final int DEFAULT_SIZE = 10;
	
	//默认用数组存储
	private Object[] values = new Object[DEFAULT_SIZE];
	
	private int arrayLength = DEFAULT_SIZE;
	
	//
	private int top = -1;
	
	private int bottom = -1;
	
	@Override
	public int size() {
		return (top - bottom) + 1;
	}

	//队列顶端删除元素
	@SuppressWarnings("unchecked")
	@Override
	public T remove() {
		if(isEmpty()){
			throw new NullPointerException();
		}
		T value = (T)values[++top];
		return  value;
	}

	//在对列底添加元素
	@Override
	public void add(T element) {
		if(bottom >= arrayLength-1){
			resize();
		}
		values[++bottom] = element;
	}

	@Override
	public boolean isEmpty() {
		return top > bottom;
	}

	@Override
	public void clear() {
		top = bottom = -1;
	}
	
	@Override
	public boolean hasElement() {
		return top < bottom;
	}
	
	public void resize(){
		arrayLength = arrayLength + DEFAULT_SIZE;
		Object[] temp = new Object[arrayLength];
		for(int i=0;i<values.length;i++){
			temp[i] = values[i];
		}
		values = temp;
	}
	
	public static void main(String args[]){
		ArrayQueue<Integer> arrayQueue = new ArrayQueue<Integer>();
		arrayQueue.add(1);
		arrayQueue.add(2);
		arrayQueue.add(3);
		arrayQueue.add(4);
		arrayQueue.add(5);
		arrayQueue.add(6);
		arrayQueue.add(7);
		arrayQueue.add(8);
		arrayQueue.add(9);
		arrayQueue.add(10);
		arrayQueue.add(11);
		while(arrayQueue.hasElement()){
			System.out.println(arrayQueue.remove());
		}
	}

	
}

public class LinkedList<T> implements Queue<T> {

	private int size = 0;
	
	private Item top ;
	
	private Item bottom;
	
	private class Item{
		private T data;
		
		private Item next;
		
		Item(T data,Item next){
			this.data = data;
			this.next = next;
		}
	}

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

	@Override
	public T remove() {
		if(--size < 0){
			throw new NullPointerException();
		}
		T value = top.data;
		top = top.next;
		return value;
	}

	@Override
	public void add(T element) {
		if(top == null){
			top = new Item(element,null);
		}else if(bottom == null){
			bottom = new Item(element,null);
			top.next = bottom;
		}else{
			Item item = new Item(element,null);
			bottom.next = item;
			bottom = item;
		}
		size ++;
	}

	@Override
	public boolean isEmpty() {
		return size == 0;
	}

	@Override
	public void clear() {
		top = bottom = null;
	}

	@Override
	public boolean hasElement() {
		if(top == null){
			return false;
		}
		return top.data != null;
	}

	public static void main(String args[]){
		LinkedList<Integer> linkedList = new LinkedList<Integer>();
		linkedList.add(1);
		linkedList.add(2);
		linkedList.add(3);
		linkedList.add(4);
		linkedList.add(5);
		linkedList.add(6);
		linkedList.add(7);
		linkedList.add(8);
		linkedList.add(9);
		linkedList.add(10);
		linkedList.add(11);
		while(linkedList.hasElement()){
			System.out.println(linkedList.remove());
		}
	}
	
}