doub in evaluation of assignment

[Divya Gehlot]

Hi,
Can any one explain me below code which expression will it evaluate first. What I expected was the answer -apple.

  public class AnyClass {
 public static void main(String[] args) { 
          boolean a = false; 
         if (a = 1 == 2) { 
              System.out.println("apple"); 
          } else { 
              System.out.println("banana"); 
          } 
      } 
  } 
 
  

[Murali Kakarla]

Hi Divya

If you see operator precedence, == have higher precedence than =.
So first 1 == 2 is evaluated which returns false and this value has been assigned to a.
Hence statement in else condition is executed.

Murali...

[dhwani mathur]

Hey murali you said

1==2 returns false
and already value of "a =false"

than false=false,returns true isnt it?
or does it return false ?
and if it returns true than it should not go to
else part but print apple

and if false =false returns false
than only it should go to else part and print.....

please explain which is right?

[Raghavan Muthu]

Basically this is what happens.

  if(a=1==2)

As the operators work on Right-to-left, first the check on (1==2) is happening.

The result of the comparison is assigned to a boolean variable.

This is compatible and without compile-time error because the result of comparison (remember! == operator and NOT = operator) would always be of type boolean (true or false).

Since the result of (1==2) is false (obviously! ), the same 'false' is assigned to the boolean variable 'a' (here you got to be careful, because you had used = operator). The result of an assignment will be the value of the expression.

So, the value 'false' is assigned to 'a' and is checked in if loop thus making the 'else' statement eligible for execution. So, you get "banana" instead of "apples" contradicting to your guess!

Just modify the same program and test:

  if(a=1==1)

This will print "apple" with the same logic explained above.

To just prove the result of assignment is the value returned, see the sample code below.

public class SampleBooleanAssignmentTest
{ 
public static void main(String[] args) 
{           
boolean flag=false;
System.out.println("flag is : "+flag);
if(flag=true)
System.out.println("TRUE");
System.out.println("(2) flag is : "+flag);
}   
} 

The output of the above program is :

flag is : false
TRUE
(2) flag is : true

The last line in the output clearly states and proves the value 'true' is being assigned and also checked for the same.

Hope this helps!

[Ulf Dittmer]

Originally posted by dhwani mathur:
than false=false,returns true isnt it?

No. "=" is not a comparison, it's an assignment. Assignments return the value that gets assigned, which in this case is "false".

[dhwani mathur]

Well!!

Thanks a lot Raghavan and UlfDittmer

i got my doubt cleared......

[Divya Gehlot]

Hi,
But in If condition we will check the condition if its true then execute if otherwise exceute else. here we instead of comparing we have assigned the value then why its going to else part.

[Ulf Dittmer]

Originally posted by Divya Gehlot:
But in If condition we will check the condition if its true then execute if otherwise exceute else. here we instead of comparing we have assigned the value then why its going to else part.

It is going to the "else" part because the condition is false. The condition in this case is the value of the assignment, which is false.

[Divya Gehlot]

now I got it thanks a alot