Question

I modified a program which creates a Queue and then add or remove items to it.

The problem in my code is that after I remove one item, and then add an item it goes into infinite loop and I’m not sure how to prevent it from happening.

My goal is to modify display() method only.

This is how I display Queue:

   public void display() 
   {
       int i = front;

           do {
               if (maxSize == nItems)
               {
                   if (i == size())
                       i = 0;

                   System.out.print(queArray[i++] + " ");
               }
               else if (maxSize < nItems)
               {
                   System.out.print("Too many queue items!");
                   break;
               }
               else
                   maxSize = nItems;
           }
           while (i != rear + 1 && !isEmpty());
       }

This is how I add and remove items:

   public void insert(long j)   // put item at rear of queue
      {
      if(rear == maxSize-1)         // deal with wraparound
         rear = -1;
      queArray[++rear] = j;         // increment rear and insert
      nItems++;                     // one more item
      }

   public long remove()         // take item from front of queue
      {
      long temp = queArray[front++]; // get value and incr front
      if(front == maxSize)           // deal with wraparound
         front = 0;
      nItems--;                      // one less item
      return temp;
      }

Answer 1

Here is the source code for the same.

import java.util.Arrays;

public class Queue {

    private int enqueueIndex;// Separate index to ensure enqueue happens at the end
    private int dequeueIndex;// Separate index to ensure dequeue happens at the
                            // start
    private int[] items;
    private int count;
    // Lazy to add javadocs please provide
    public Queue(int size) {
        enqueueIndex = 0;
        dequeueIndex = 0;
        items = new int[size];
    }
    // Lazy to add javadocs please provide
    public void enqueue(int newNumber) {
        if (count == items.length)
            throw new IllegalStateException();
        items[enqueueIndex] = newNumber;
        enqueueIndex = ++enqueueIndex == items.length ? 0 : enqueueIndex;
        ++count;
    }
    // Lazy to add javadocs please provide
    public int dequeue() {
        if (count == 0)
            throw new IllegalStateException();
        int item = items[dequeueIndex];
        items[dequeueIndex] = 0;
        dequeueIndex = ++dequeueIndex == items.length ? 0 : dequeueIndex;
        --count;
        return item;
    }

    @Override
    public String toString() {
        return Arrays.toString(items);
    }
}