Regarding java.util.Queue

[Krishna Potluri]

Hi,

How to read all elements from java.util.Queue using peek()?. Kindly reply me back. Thanks in advance.

One way of getting the elements from java.util.Queue implementation classes is using poll(),but this method removes the elements from the Queue.Code is as follows:
___________________________________________________________________________
//************* with repective to JDK1.5************

import java.util.Queue;
import java.util.LinkedList;
import org.apache.log4j.*;

public class QueueOffer {
private static Category category = Category.getInstance(QueueOffer.class.getName());
public static void main(String[] args) {
Queue queue = new LinkedList();
//Add Items To Queue

queue.offer("Sri");
queue.offer("Krishna");
queue.offer("Prasad");
queue.offer("Potluri");

category.info("...Adding Items To Queue..."+queue.toString());

// Retrive Items From Queue.
category.info("....Retriving The Items From Queue... ");
//Iterator iterate = queue.iterator();
Object o;

while( (o=queue.poll())!= null ) {

category.info(" "+o);

}

}
____________________________________________________________________________

My requirement is just read all elements from the Queue , but elements should not be deleted. This can be done using peek(). But I would like to know how?

Thanks & Regards,
Kris.

[Chandra Bhatt]

Hi Krishna,

My requirement is just read all elements from the Queue , but elements should not be deleted. This can be done using peek().

peek() returns the top of the elements in the queue.


Simply do this, if you want to read elements from the queue in the order,
peek follows:

public class UsingQueue {
 
public static void main(String... args) {
Queue<String> q = new LinkedList<String>();
q.offer("aroma");
q.offer("dodgems");
q.offer("elegant");
q.offer("biscuit");
q.offer("cyber");

System.out .println(q);
}
}

peek() doesn't modify the queue; it simply shows an element from the front of the queue.
"Insertion from rear, deletion from front" It's queue


Regards,
cmbhatt
[ April 20, 2007: Message edited by: Chandra Bhatt ]

[Jim Yingst]

Remember that a Queue is also a Collection. So you can simply use the iterator() method to iterate through all the values, without removing them. This is also done implicitly by a for loop:

for (Foo f : queue) {
    System.out.println("element: " + f);
}

Be aware that the order of iteration is not guaranteed to be the same as the order in which elements would be removed using poll(). For many implementations, including LinkedList, it is the same. But not always.

[Chandra]: "Insertion from rear, deletion from front" It's queue

That's a FIFO queue. The java.util.Queue interface is more general than that; it may instead be a FILO queue (a stack), or a priority queue, or some other ordering.

[Chandra Bhatt]

That's a FIFO queue. The java.util.Queue interface is more general than that; it may instead be a FILO queue (a stack), or a priority queue, or some other ordering.

Thanks Jim!

It means queue is not necessarily FIFO. So far Java Queue is concerned, it can be FIFO (general queue), FILO(stack), or priority queue (todo list).


Thanks for clarification, Jim!


Regards,
cmbhatt

[Krishna Potluri]

Hi Jim,

Thanks for spending your most valuable time to answer my doubt.


Thanks and Regards,
Kris.