java中如何实现队列的入队与出队

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//数据结构——队列
import java.util.Scanner;
public class Queue {
	int[] a ;
	int rear;
	int front;
	int maxsize;
	
	public static void main(String[] args) {
		Queue queue = new Queue();
		Scanner scan = new Scanner(System.in);
		int i;
		do {
			System.out.println("请输入：1入队   2出队   3查看   0退出");
			i = scan.nextInt();
			switch(i) {
				case 1:
					System.out.println("请输入要入队的元素：");
					queue.addQueue(scan.nextInt());
					break;
				case 2:
					queue.exitQueue();
					break;
				case 3:
					queue.showqueue();
					break;
			}
		}while(i!=0);
		System.out.println("退出成功");
	}
	
	//构造函数
	public Queue(){
		a = new int[4];
		rear = 0;
		front = 0;
		maxsize = 4;
	}
	
	//判断队列是否为空
	public boolean judgeNull() {
		return rear == front;
	}
	
	//判断队列是否已满
	public boolean judgeFull() {
		return (rear+1) % maxsize == front;
	}
	
	//入队
	public void addQueue(int num) {
		//判断，若队列已满则结束，不满则将其添加
		if(judgeFull()) {
			System.out.println("队列已满");
			return ;
		}
		a[rear] = num;
		rear = (rear+1) % maxsize;
	}
	 
	//出队
	public void exitQueue() {
		//判断，若队列为空则结束，非空则将其最前的元素取出
		if(judgeNull()) {
			System.out.println("队列为空");
			return ;
		}
		front = (front+1) % maxsize;
	}
	
	//显示队列的元素
	public void showqueue() {
		if(judgeNull()) {
			System.out.println("队列为空");
			return ;
		}
		for (int i = front; i < front+count(); i++) {
			System.out.printf("a[%d] = %dn",i%maxsize,a[i%maxsize]);
		}
	}
	
	//求出队列的有效个数
	public int count() {
		return (rear+maxsize-front)%maxsize;
	}
}