Best implementation of Java Queue?

Question

I am working (in Java) on a recursive image processing algorithm that recursively traverses the pixels of the image, outwards from a center point.

Unfortunately, tha

Answer 1

However, if you still want to use the recursive algorithm, you can change it to be "tail-recursive" which probably is optimized in the JVM to avoid stack overflows.

Answer 2

I think you can some up with simple like implementation

package DataStructures;

public class Queue<T> {

   private Node<T> root;

   public Queue(T value) {
      root = new Node<T>(value);
   }

   public void enque(T value) {
      Node<T> node = new Node<T>(value);
      node.setNext(root);
      root = node;
   }

   public Node<T> deque() {

      Node<T> node = root;
      Node<T> previous = null;

      while(node.next() != null) {
         previous = node;
         node = node.next();
      }
      node = previous.next();
      previous.setNext(null);
      return node;
   }

   static class Node<T> {

      private T value;
      private Node<T> next;

      public Node (T value) {
         this.value = value;
      }

      public void setValue(T value) {
         this.value = value;
      }

      public T getValue() {
         return value;
      }

      public void setNext(Node<T> next) {
         this.next = next;
      }

      public Node<T> next() {
         return next;
      }
   }
}

Answer 3

Here is the Queue Implementation with Iterator and Iterable interface

Queue Size will increase as It gets full

Queue Interface

package com.practice.ds.queue;

import com.practice.ds.queue.exception.QueueException;

public interface QueueInterface<T> {

    public boolean empty();

    public void enqueue(T item);

    public void dequeue() throws QueueException;

    public T front() throws QueueException;

    public void clear();
}

Custom Exception Class

package com.practice.ds.queue.exception;

public class QueueException extends Exception {

    private static final long serialVersionUID = -884127093599336807L;

    public QueueException() {
        super();
    }

    public QueueException(String message) {
        super(message);
    }

    public QueueException(Throwable e) {
        super(e);
    }

    public QueueException(String message, Throwable e) {
        super(message, e);
    }
}

Implementation of Queue

package com.practice.ds.queue;

import java.util.Iterator;

import com.practice.ds.queue.exception.QueueException;

public class Queue<T> implements QueueInterface<T>, Iterable<T> {

    private static final int DEFAULT_CAPACITY = 10;
    private int current = 0;
    private int rear = 0;
    private T[] queueArray = null;
    private int capacity = 0;

    @SuppressWarnings("unchecked")
    public Queue() {
        capacity = DEFAULT_CAPACITY;
        queueArray = (T[]) new Object[DEFAULT_CAPACITY];
        rear = 0;
        current = 0;
    }

    @Override
    public boolean empty() {
        return capacity == current;
    }

    @Override
    public void enqueue(T item) {
        if(full())
            ensureCapacity();
        queueArray[current] = item;
        current++;
    }

    @Override
    public void dequeue() throws QueueException {
        T dequeuedItem = front();
        rear++;
        System.out.println("Dequed Item is " + dequeuedItem);
    }

    @Override
    public T front() throws QueueException {
        return queueArray[rear];
    }

    @Override
    public void clear() {
        for (int i = 0; i < capacity; i++)
            queueArray[i] = null;
        current = 0;
        rear = 0;
    }

    @SuppressWarnings("unchecked")
    private void ensureCapacity() {
        if (rear != 0) {
            copyElements(queueArray);
        } else {
            capacity *= 2;
            T[] tempQueueArray = (T[]) new Object[capacity];
            copyElements(tempQueueArray);
        }
        current -= rear;
        rear = 0;
    }

    private void copyElements(T[] array) {
        for (int i = rear; i < current; i++)
            array[i - rear] = queueArray[i];
        queueArray = array;
    }

    @Override
    public Iterator<T> iterator() {
        return new QueueItearator<T>();
    }

    public boolean full() {
        return current == capacity;
    }

    private class QueueItearator<T> implements Iterator<T> {

        private int index = rear;

        @Override
        public boolean hasNext() {
            return index < current;
        }

        @SuppressWarnings("unchecked")
        @Override
        public T next() {
            return (T) queueArray[index++];
        }
    }

}