About Question enthuware.ocajp.i.v7.2.1280 :

[admin]

Yes, sorry, I meant x==0 is true.

[Meghana]

I tried to run it by adding package and main method like this:

Code: Select all

package happeningPackage;

public class TestClass {

   public static void main(String[] args) {}
   public void loopTest(int x){
      loop: for (int i = 1; i < 5; i++){
         for (int j = 1; j < 5; j++){
            System.out.println(i);
            if (x == 0) {  continue loop;  }
            System.out.println(j);
         }
      }}}

I'm not getting any output. What is wrong with the code?
(I'm a newbie. Studied and then started with mocks but new to practical coding. Please help!)
(When I tried to include loopTest within the main method, there were other errors, like: loopTest cannot have void return type.) So, how could I change the code?

[admin]

Please post exact error message that you get. Screenshot would be even better.

[Meghana]

Here is the snap when I ran it.
(Hope its not too difficult to read. Had to reduce resolution and compress it to keep it within the limit:256kb)

[admin]

I don't see any meaningful information in the Eclipse screen shot that you've posted.
As I mentioned to you before in another thread, you need to use the command line to compile and run the code. So please try compiling it on command line and post the exact error message that you get.

If you are a beginner, you should simply avoid using any IDE at this stage.

[Meghana]

Yeah. I'll do that, although I have managed to run many other programs on eclipse. I couldn't figure as to why this wasn't giving any output

Thank you, for all the guidance though!

[admin]

Well, from the code that you've posted the main method is empty. I don't see loopTest method being called. So no output.

[Meghana]

Oh right. Thank you..

[OCAJO1]

Why is that the compiler does not complain about the System.out.println(j); being unreachable?

[admin]

Why is that the compiler does not complain about the System.out.println(j); being unreachable?

Please go through this thread from the beginning. It is explained in detail.

[juliusacar]

When x is 0, the statement continue loop; is executed. Note that loop: is for the outer loop.

Can anyone explain this to me:

loop: for (int i = 1; i < 5; i++){

I'm used to simply seeing nested for loops.

But this one have "loop:" before it. How does it work? thank you.

[admin]

You can apply a label to any statement. Since a for statement is just like any other statement, you can apply a label to a for statement as well. That is exactly what loop: is in this case.

You can read more about labels here: https://howtodoinjava.com/java/basics/l ... s-in-java/

Labels are use mostly in conjunction with break and continue statements. You can read more about it here: https://www.journaldev.com/980/java-bre ... ment-label

[vilasa]

Think about it this way. How do "you" know that it is unreachable? You know it because you know that x is 0 and x==0 will be false. You have executed the code in your mind and made that determination.

But the compiler doesn't know that x will be 0 at runtime. It cannot execute code. It can only make use of the information that it is 100% sure about at compile time. This means if you have a final variable, then the compiler can make use of that fact because it knows that its value will be the same at run time also. But a normal variable's value can be different.

You may go through this interesting discussion: http://stackoverflow.com/questions/3795 ... iler-error

So I tried the code by making x final. It still doesn't give unreachable code error.Below is my code

public class TestClass6{
final int x=0;
public void loopTest(){
loop: for (int i = 1; i < 5; i++){
for (int j = 1; j < 5; j++){
System.out.println(i);
if (x == 0) { continue loop; }
System.out.println(j);
}
}
}

public static void main(String args[]){
new TestClass6().loopTest();
}

}

[admin]

Please go through the SOF link given in the post that you've quoted. if statement is an exception. Java language allows an unreachable if block to support conditional compilation.

[vilasa]

Thank you . Yeah now I remember from other post of your's.if statement is an exception. I understand now. So for infinite loop case if there is statement after the loop ,it is unreachable . But for if condition it is exception. Is my understanding right?

[admin]

Yes, correct.

[DazedTurtle]

Okay, I understand the question just fine, and I got it right, but I like reading the explanations just in case I come across a small detail I was unaware of, and I can't understand what's being said here:

So, only one iteration (that too not full) is performed for the inner loop.

The bolded bit makes no sense to me. I don't know if there's a word missing or if there's a grammar error or if my brain's just having issues parsing it, but I can't figure out what you mean.

[admin]

The only iteration that occurs for this loop is not executed fully because of if (x == 0) { continue loop; } part. The last statement of the inner loop is not executed.

[nerdchieftain]

The code

Code: Select all

loop:

and

Code: Select all

continue loop;

is unfamiliar to me.

I assume this is a label or the language now allows naming a loop (and here the name used is loop). I cannot figure out what to call this language feature in order to search for it and learn more. What is it?

[admin]

Yes, loop is a label. continue <label>; can be found under labelled break and continue section.
https://docs.oracle.com/javase/tutorial ... ranch.html

[Denyo1986]

In another question (dont remember the number unfortunately) there was a similar case with break labels. In that question it said that the label needs to be in the same context as the break/continue statement, otherwise it becomes unreachable / not known to the break/continue statement.
If my memory is correct, the example was very very similar. And I would have thought that here, in this question, the continue loop; statement does not see the loop label as it is outside of another FOR loop.

Could you please comment on this? Maybe you know which question I mean? It would be great if you could explain the difference or a clear explanation in what context (i.e. how far) labels are known.

Thanks a lot for your hel

[admin]

You might have seen something similar in the explanation to question 2.1281. But it is not the same. That explanation is talking about the location of break and continue with labels.
If you use a break/continue with a label, then that label must be on a block that is enclosing the break/continue statement.

You can apply a label to any statement in general. There is no restriction. But you can't just break to any label. (otherwise, that would amount to a goto statement, which, of course, java does not have.)

[Denyo1986]

OK, thanks for the explanation. The question you refer to is not the one I meant. If I find it again, I will let you know.

But how is it defined, what a block is, where it starts and where it ends??
Cannot find clear information about this.

Here, if I remember correctly, the break statement was in a loop. The label before the for loop. Seems to me like two different blocks. I am missing clear borders/clear understanding where this starts and ends.

Can you point me in the right direction, please?

[admin]

You may go through section 14.15 The break Statement of JLS 11 (or the section with the same title in JLS 8).

Observe this statement from this section:

A break statement must refer to a label within the immediately enclosing method, constructor, or initializer. There are no non-local jumps. If no labeled statement with Identifier as its label in the immediately enclosing method, constructor, or initializer contains the break statement, a compile-time error occurs.

You may check out the details of the continue statement as well in the same chapter.

[Denyo1986]

http://enthuware.com/forum/viewtopic.php?f=2&t=2236

This is the question I was referring to. And now I understand the difference. Because JILL is not followed by brackets {}, its scope is only the following statement (the println()) which doesnt make sense as you can never actually break to this label. So in order to make this work, one would have to add brackets after JILL and include the if and else part).