Java队列实现

队列数组实现：队列长度有限，但是考虑到平时一般都使用有界队列，这应该也不算是个缺点

public class Queue {
	private Object[] objs;
	private int head;
	private int end;
	private int size;
	
	public Queue(int size){
		objs = new Object[size];
		this.head = 0;
		this.end = -1;
		this.size = 0;
	}
	
	public void push(Object obj) throws Exception{
		if(this.size > objs.length)
			throw new Exception("Queue is full!");
		if(end == objs.length - 1)
			end = -1;
		objs[++end] = obj;
		size++;
	}
	
	public Object pop() throws Exception{
		if(this.size == 0)
			throw new Exception("Queue is empty!");
		Object tmp = objs[head++];
		if(head == objs.length)
			head = 0;
		size--;
		return tmp;
	}
	
	public Object peek() throws Exception{
		if(this.size == 0)
			throw new Exception("Queue is empty!");
		return objs[head];
	}
	
	public int size(){
		return this.size;
	}
	
	public boolean isEmpty(){
		return (size == 0);
	}
	
	public boolean isFull(){
		return (size == objs.length);
	}
}

插入和删除的时间复杂度都为O(1)

 

队列双端链表实现：

public class FirstLastList {
	private class Data{
		private Object obj;
		private Data next = null;
		
		Data(Object obj){
			this.obj = obj;
		}
	}
	
	private Data first = null;
	private Data last = null;
	
	public void insertFirst(Object obj){
		Data data = new Data(obj);
		if(first == null)
			last = data;
		data.next = first;
		first = data;
	}
	
	public Object deleteFirst() throws Exception{
		if(first == null)
			throw new Exception("empty");
		Data temp = first;
		if(first.next == null)
			last = null;
		first = first.next;
		return temp.obj;
	}
			
	public void display(){
		if(first == null)
			System.out.println("empty");
		System.out.print("first -> last : | ");
		Data cur = first;
		while(cur != null){
			System.out.print(cur.obj.toString() + " | ");
			cur = cur.next;
		}
		System.out.print("\n");
	}
}

public class FirstLastListQueue {
	private  FirstLastList fll = new FirstLastList();

	public void push(Object obj){
		fll.insertLast(obj);
	}
	
	public Object pop() throws Exception{
		return fll.deleteFirst();
	}
	
	public void display(){
		fll.display();
	}
	
	public static void main(String[] args) throws Exception{
		FirstLastListQueue fllq = new FirstLastListQueue();
		fllq.push(1);
		fllq.push(2);
		fllq.push(3);
		fllq.display();
		System.out.println(fllq.pop());
		fllq.display();
		fllq.push(4);
		fllq.display();
	}
}

first -> last : | 1 | 2 | 3 | 
1
first -> last : | 2 | 3 | 
first -> last : | 2 | 3 | 4 | 

长度不受限制并且插入和删除的时间复杂度都为O(1)