我如何在java中排队？

Question

I want to shift the elements in the array in a queue style. I did this code:

public class Queue {
    private int[] elements;
    private int size;
    public static final int DefCap = 8;

    public Queue() {
        this(DefCap);
    }

    public Queue(int capacity) {
        elements = new int[capacity];
    }

    public int[] enqueue(int v) {
        if (size >= elements.length) {
            int[] a = new int[elements.length * 2];
            System.arraycopy(elements, 0, a, 0, elements.length);
            elements = a;
        }
        elements[size++] = v;
        return elements;
    }

    public int dequeue() {
        return elements[--size];
    }
    public boolean empty() {
        return size == 0;
    }
    public int getSize() {
        return size;
    }

}

How can I shift the numbers in the array where the next number added pushes the last one? because all it does now is removes the last one added (Stacking).

Answer 1

First, remember that it doesn't matter at all how you add or retrieve the elements as long as it appears that the operation reflects that of a queue (ie FIFO ). The internals of your implementation are of no concern to the user(s). The easiest method (imo) is to add them normally to the end and "remove" them from the beginning.

When you add the new element, do it like you are already doing it.

When you remove the first element, do it virtually by using an index.

int nextIdx = 0; // initialize start of queue
...
...
public int next() {
   if (nextIdx < elements.length) {
       return elements[nextIdx--];
   } 
   // indicate an error by throwing an exception
}

At some point you are going to want to reclaim the "non-existent" elements at the beginning of the queue and then reset nextIdx . You can do this when you need to resize the array. You can use System.arraycopy and make use of both the value of nextIdx and the new desired new size to resize the array and copy the remaining elements.

Note: In your enqueue method I'm not certain why you want to return the entire element array when you add an element. I would expect something like returning the element just added, a boolean indicating success, or not return anything.