About Question enthuware.ocajp.i.v7.2.1114 :

[Michailangelo]

Shouldn't this print 5?

[Michailangelo]

I see now. The while is a never ending loop.

[akassem]

I understand that the while loop is an infinite loop. But since it calls getX() each time, shouldn't this lead to a StackOverflowError eventually?

[admin]

I understand that the while loop is an infinite loop. But since it calls getX() each time, shouldn't this lead to a StackOverflowError eventually?

No, stack overflow occurs in recursion. i.e. when a method calls itself. That is not happening here.

HTH,
Paul.

[crux terminatus]

To check my understanding:

getX() will return 5 each time the condition in the while loop is checked. So, the condition 5 != 0 will be checked each time the while loop is executed, and will always be false - thus the infinite loop.

If int x = 0 is removed, x will eventually become 0, upon which the while loop terminates.

Correct?

[admin]

Yes, that is correct.

[UmairAhmed]

Hi,

Can you please illustrate what actually the local variable 'x' in method looper() do and its effect on while loop. Why while loop just stops if we remove int x = 0 from the lopper method(). I guess it is something related with shadowing of instance variable with local variable but couldn't get this point.

[admin]

Did you read the explanation? It explains exactly what you are asking.

Note that looper() declares an automatic variable x, which shadows the instance variable x. So when x = m; is executed, it is the local variable x that is changed not the instance field x. So getX() never returns 0. If you remove int x = 0; from looper(), it will print 0 and end.

If you remove the automatic variable x, then there will be no shadowing of the instance field x and x = m will affect the instance field x.

Also, please read the post by "crux terminatus" above.

[wuqing1450]

Did you read the explanation? It explains exactly what you are asking.

Note that looper() declares an automatic variable x, which shadows the instance variable x. So when x = m; is executed, it is the local variable x that is changed not the instance field x. So getX() never returns 0. If you remove int x = 0; from looper(), it will print 0 and end.

If you remove the automatic variable x, then there will be no shadowing of the instance field x and x = m will affect the instance field x.

Also, please read the post by "crux terminatus" above.

If local x to be changed to this.x, the code would print 0. Correct?

Code: Select all

public class TestClass{
        int x = 5;
        int getX(){ return x; }

        public static void main(String args[]) throws Exception{
            TestClass tc = new TestClass();
            tc.looper();
            System.out.println(tc.x);
        }
        public void looper(){
            int x = 0;
            while( (this.x = getX()) != 0 ){
                for(int m = 10; m>=0; m--){
                    [b]this.[/b]x = m;
                }
            }
       }     
}

[admin]

What happened when you tried it out?

[wuqing1450]

What happened when you tried it out?

It prints 0

[Sai Divya sree]

What will the following code print?

Code: Select all

public class TestClass{
        int x = 5;
        int getX(){ return x; }

        public static void main(String args[]) throws Exception{
            TestClass tc = new TestClass();
            tc.looper();
            System.out.println(tc.x);
        }
        
        public void looper(){
            int x = 0;
            while( (x = getX()) != 0 ){
                for(int m = 10; m>=0; m--){
                    x = m;
                }
            }
            
       }     
}

Hi,
i couldn't understand how if int x=0 is removed from looper(); method would result in printing 0 and end?Though i have seen the earlier posts i couldnt understand the replies.Please if anyone could help me.I am little new to JAVA.Thank you!

[admin]

If you remove int x=0 from looper, there will be only one variable named x in the whole code and that is the instance variable x. This x will be modified in look by the statement x = m; At the end of the loop, x will be assigned 0.

[Sai Divya sree]

Wow!Thank you .I understood it very well!

[sherryyuan]

I just wonder how this code will compile since x is an instance variable in the class. and the loop declare it with the same name? Is it work?

[admin]

What happened when you tried it out?

[seemavishwakarma]

Why this code compiles and do not complain about unreachable System.out.println statement due to infinite loop.

[admin]

Compiler does not execute code. It does not know the value of the variables (unless they are compile time constants). So it does not know that it is an infinite loop.

[seemavishwakarma]

Thanks a lot Enthuware. Cleared my certification 1Z0-803 . Tests helped me a lot. definitely a must have before actual exams!!!

[Javier]

Hi!!

I would like to know if an infinite loop generate some kind of exception or error, is there no problem with the memory or the hard disk?

[admin]

Hi!!

I would like to know if an infinite loop generate some kind of exception or error, is there no problem with the memory or the hard disk?

A simple for loop that does not consume any memory can run forever -
for(;;);

If the loop consumes memory, of course, it will eventually cause OutOfMemoryError or StackOverflowError (if there is recursion involved).

[Javier]

Thank you so much Admin for your answer!!
Enthuware is great, I learnt a lot of with your explanations, I feel very confident to try to pass the OCA certificate.
Thank you guys!!

[SeoaneR]

Hi There
I'm finding the !=(Not equals) quite confusing .
The interpretation of the != operator is that , if values are not equal then the condition evaluates to true,
or evaluating to true if the values are different.
The while loop has the following condition : while(x = getX() !=0) .This implies 5 !=0 .So if I use the definition
of the != that says if values are not equal the condition evaluates to true ...why does the while loop evaluate
to false.

[admin]

You understanding is correct. while loop does not evaluate to false. It evaluates to true. Why do you think it evaluates to false here?

[OCAJO1]

So the fact that the correct answer is that it will run forever and not throw an exception (OutOfMemeoryException) at run time, mean that neither the for loop nor the assignment within it (x=m) consume any memory?