java的Queue的问题

Question

可以请教一下怎么修改代码才能出这样的输出呢

public class Queue {
    private Double[] values;
    private int front;
    private int rear;
    private int counter;
    
    public Queue(int size) {
        values = new Double[size];
        front = 0;
        rear = -1;
        counter = 0;
    }
    public boolean isEmpty() {
        if(this.front == this.rear) {
            return true;
        }
        return false;
    }
    public boolean isFull() {
        if(front == (rear+1) % values.length) {
            return true;
        }
        return false;
    }
    public Double enqueue(double x) {
        if(isFull()) {
            return null;
        }else {
            rear = (rear + 1) % values.length;
            values[rear] = Double.valueOf(x);
            counter++;
            return values[rear];
        }
    }
    public Double dequeue() {
        if(isEmpty()) {
            return null;
        }else {
            
            front = (front + 1) % values.length;
            counter--;
            return values[front];
        }
    }
    public void displayQueue() {
        if(isEmpty()) {
            System.out.println("Empty queue!");
            return;
        }
        System.out.print("front-> ");
        for(int i = 0; i < values.length; i++) {
            System.out.println(values[i]);
        }
            }
    public static void main(String[] args) {
        Queue myQueue = new Queue(4);
        myQueue.enqueue(-2);
        myQueue.enqueue(3);
        myQueue.enqueue(1);
        System.out.println("The queue has 3 items: -2, 3, 1");
        myQueue.displayQueue();
        myQueue.enqueue(8);
        myQueue.enqueue(6);
        System.out.println("The queue has 4 items: -2, 3, 1, 8");
        myQueue.displayQueue();        
        myQueue.dequeue();
        myQueue.dequeue();
        System.out.println("The queue has 2 items: 1, 8");
        myQueue.displayQueue();
        myQueue.dequeue();
        myQueue.dequeue();
        myQueue.dequeue();
        System.out.println("The queue is empty:");
        myQueue.displayQueue();

    }
    

}

我想要的效果：

The queue has 3 items: -2, 3, 1
front -> | -2.0000 |
| 3.0000 |
| 1.0000 | < - rear
The queue has 4 items: -2, 3, 1, 8
front -> | -2.0000 |
| 3.0000 |
| 1.0000 |
| 8.0000 | < - rear
The queue has 2 items: 1, 8
front -> | 1.0000 |
| 8.0000 | < - rear
The queue is empty:
Empty queue!

运行结果及报错内容 ：

The queue has 3 items: -2, 3, 1
front-> null
null
null
null
The queue has 4 items: -2, 3, 1, 8
front-> null
null
null
null
The queue has 2 items: 1, 8
front-> null
null
null
null
The queue is empty:
front-> null
null
null
null

Answer 1

题主的代码主要是 isEmpty，isFull 和 displayQueue 三个方法有问题，需要修改一下

public class Queue {
    private Double[] values;
    private int front;
    private int rear;
    private int counter;

    public Queue(int size) {
        values = new Double[size];
        front = 0;
        rear = -1;
        counter = 0;
    }
    public boolean isEmpty() {
        return counter == 0;
    }
    public boolean isFull() {
        return counter == values.length;
    }
    public Double enqueue(double x) {
        if(isFull()) {
            return null;
        }else {
            rear = (rear + 1) % values.length;
            values[rear] = x;
            counter++;
            return values[rear];
        }
    }
    public Double dequeue() {
        if(isEmpty()) {
            return null;
        }else {
            front = (front + 1) % values.length;
            counter--;
            return values[front];
        }
    }
    public void displayQueue() {
        if(isEmpty()) {
            System.out.println("Empty queue!");
            return;
        }
        System.out.print("front-> ");
        for(int i = front; i <= rear; i++) {
            System.out.println(values[i]);
        }
        System.out.println("<-rear");
    }
    public static void main(String[] args) {
        Queue myQueue = new Queue(4);
        myQueue.enqueue(-2);
        myQueue.enqueue(3);
        myQueue.enqueue(1);
        System.out.println("The queue has 3 items: -2, 3, 1");
        myQueue.displayQueue();
        myQueue.enqueue(8);
        myQueue.enqueue(6);
        System.out.println("The queue has 4 items: -2, 3, 1, 8");
        myQueue.displayQueue();
        myQueue.dequeue();
        myQueue.dequeue();
        System.out.println("The queue has 2 items: 1, 8");
        myQueue.displayQueue();
        myQueue.dequeue();
        myQueue.dequeue();
        myQueue.dequeue();
        System.out.println("The queue is empty:");
        myQueue.displayQueue();
    }
}