PriorityQueue Question

[Sanjeev Singh]

public class PriorityTest {
    public static void main(String[] args) {
      Queue q = new PriorityQueue();
      q.offer(">Java<");
      q.offer(">java<");
      q.offer("> Java<");
      q.offer("> java<");
      q.offer(">$<");
      for (int i = 0; i < q.size(); i++) {
          System.out.println(q.poll());
      }
    }
}

I have two question.
(A) Why this program gives comilation warning?
(B) Output

[Barry Gaunt]

What does the warning message mean to you? Why not tell us the warning message you are getting?

To get the output you can run the program. Please show some effort to find the solution.

[Sanjeev Singh]

While compilation
without -Xlint:unchecked option to javac
Note: C:\nbworkspace\SCJPKSBB\src\PriorityTest.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
with -Xlint:unchecked option to javac
C:\nbworkspace\SCJPKSBB\src\PriorityTest.java:21: warning: [unchecked] unchecked call to offer(E) as a member of the raw type java.util.Queue
q.offer(">Java<");
C:\nbworkspace\SCJPKSBB\src\PriorityTest.java:22: warning: [unchecked] unchecked call to offer(E) as a member of the raw type java.util.Queue
q.offer(">java<");
C:\nbworkspace\SCJPKSBB\src\PriorityTest.java:23: warning: [unchecked] unchecked call to offer(E) as a member of the raw type java.util.Queue
q.offer("> Java<");
C:\nbworkspace\SCJPKSBB\src\PriorityTest.java:24: warning: [unchecked] unchecked call to offer(E) as a member of the raw type java.util.Queue
q.offer("> java<");
C:\nbworkspace\SCJPKSBB\src\PriorityTest.java:25: warning: [unchecked] unchecked call to offer(E) as a member of the raw type java.util.Queue
q.offer(">$<");
5 warnings

I got these warnings.

Barry,I know the output but want the Ranchers to have a look and solve.

[Marcus Green]

I don't quite understand, did you ask the question because you wanted to know the answer?

[Sanjeev Singh]

No I didn't mean that. I have got the answer for ( B ) but ( A ) is still unanswered.

[Henry Wong]

Originally posted by Sanjeev Kumar Singh:
No I didn't mean that. I have got the answer for ( B ) but ( A ) is still unanswered.

Sanjeev,

You have to keep in mind that this site is also for learning. You have to show some effort that you are working towards the solution -- asking what is the output gives the impression that you never ran it yourself.


Anyway, the warning errors are caused by your use of generics. They are only warning errors and you may ignore them if you like... but to learn more, you may try the Sun tutorial on Generics.

Henry

[Barry Gaunt]

Apart from Sun's tutorial there is also an entry in Angelika Langer's Generic FAQ

[Sanjeev Singh]

Henry and Barry,
Thanks for the help.I will try to be more specific towards questioning next time.
[ November 23, 2006: Message edited by: Sanjeev Kumar Singh ]

[B pandoo]

i have a doubt.i coplied the program i got the ouput as

(space)Java
(space)java
$
usually queue will sort it,so i am getting the above 3 output.but
i want to know what happenened to the other two entries
(without space)java and (without space)Java.
please let me know.

[Barry Gaunt]

Originally posted by B pandoo:
i have a doubt.i coplied the program i got the ouput as

(space)Java
(space)java
$
usually queue will sort it,so i am getting the above 3 output.but
i want to know what happenened to the other two entries
(without space)java and (without space)Java.
please let me know.

Yes, it's a tricky one - not fair really.

q.poll() removes the element from the queue. So think about the value of q.size() as you execute the loop. How many times does the loop execute if the size is changing.

When you have that sorted out, fix the program so that you get all five elements.

[Marcus Green]

Sanjeev, knowing how to ask a question well is an art in itself. We dont mean to "wag our fingers" at you when we comment on the style of your asking. Don't be put off by our comments, keep posting and asking (and even answering) questions.

[Burkhard Hassel]

Hi ranchers,

To Sanjeev:
this warning occurs, when you use a generic class without parameterizing it.

To B pandoo:
perhaps try
System.out.println("index i:"+i + " size:"+q.size());
after the line with the poll, and have a look at the output.


Yours,
Bu.

[B pandoo]

Thanks group.now i am clear