Java program to implement Queue

A stack is a collection where insertion and deletion happens in the same end ( LIFO)
In Queue an insertion or updates should occurs on one end , that we called tail/rear
Any removal should happens on the other end, that we called front/head

Operations available with Queue

* insertion is called enqueue operation ( push)
* deletion is called dequeue operation (pop)
* peek() to return the front element
* isEmpty()
* isFull()




/**
 * Implementing queue in java using
 *
 * Here i wrote a sample program to implement queue in java
 *
 */
package com.belazy.algorithm;

/**
 * @author consumerfed Triveni kozhikode
 *
 */
public class QueueADT {

private Object[] queueArray = null;
private int MAX_SIZE = 5;
int front = 0; // head of the queue
int rear = 0; // tail
int size = 0;

public QueueADT() {
queueArray = new Object[MAX_SIZE];
}

public void enqueue(Object value) {
if (!isFull()) {
queueArray[rear] = value;
rear = rear - 1;
if (rear < 0) {
rear = MAX_SIZE - 1;
}
size = size + 1;
System.out.println(" value :"+value + " front :"+front + "rear : "+rear);
} else {
System.out.println(" The Queue is full ");
}

}

 public Object dequeue() { Object obj = null; if (isEmpty()) { System.out.println(" The Queue is empty "); } else { obj = queueArray[front]; queueArray[front] = null; front = front - 1; if (front < 0) { front = MAX_SIZE - 1; } size = size - 1; System.out.println(" value :"+obj + " front :"+front + "rear : "+rear); System.out.println(" The element removed is "+obj); } return obj; }

public void peek() {
if (!isEmpty())
System.out.println(" The front element is " + queueArray[front]);
}

private boolean isEmpty() {
if (size == 0) {
return true;
}
return false;

}

private boolean isFull() {
if (size == MAX_SIZE) {
return true;
}
return false;
}

public void showElements() {
int i = 0;
for (Object obj : queueArray) {
System.out.println(i + " th position element is " + obj);
i++;
}
}

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub

QueueADT queueADT = new QueueADT();
queueADT.enqueue(new Integer(1));
queueADT.enqueue(new Integer(2));
queueADT.enqueue(new Integer(3));
queueADT.enqueue(new Integer(4));
queueADT.enqueue(new Integer(5));
queueADT.enqueue(new Integer(6));

queueADT.peek();

// queueADT.showElements();

queueADT.dequeue();

queueADT.peek();

// queueADT.showElements();
queueADT.enqueue(new Integer(6));
queueADT.peek();

}

}


Output

 value :1 front :0rear : 4
 value :2 front :0rear : 3
 value :3 front :0rear : 2
 value :4 front :0rear : 1
 value :5 front :0rear : 0
 The Queue is full
 The front element is 1
 value :1 front :4rear : 0
 The element removed is 1
 The front element is 2
 value :6 front :4rear : 4
 The front element is 2