if - boolean

[Arnb Sen]

This code compiles and runs with NO output. Cannot understand why ?

public class class2 {
   public static void main(String argv[]){
      class2 mi = new class2();
   }
   class2() {
      boolean b = false;
      if(b=false){
          System.out.println("b is "+b);
      }
   }
}

[Henry Wong]

What were you expecting? The print statement is in a condition that is set to false.

Henry

[Jim Yingst]

if(b=false){

Normally an if statement would not compile if you replace == with =. However in this case it compiles, because b is boolean. An assignment (=) has the side effect of returning the value assigned, which means for example

int x;
int y;
x = (y = 1);

Here the last statement assign y = 1, and then assigns x = 1. Because (y = 1) not only assigns y = 1; it also evaluates to 1. So

x = (y = 1);

is the same as

y = 1;
x = (1);

Similarly,

if(b=false){

is the same as

b=false;
if(false){

[ November 27, 2005: Message edited by: Jim Yingst ]

[Campbell Ritchie]

You don't need to use = or == in the if () statement when dealing with a boolean primitive variable. You just write

 boolean myBoolen = *****;
 if(myBoolean)
   {
      anotherStatement();
   } etc etc 

[Campbell Ritchie]

. . . and I forgot you want it to work if myBoolean is false. Then all you have to write is,

if(!myBoolean) etc etc  

CR

[Arnb Sen]

Thank you everyone.

[Campbell Ritchie]

That's a pleasure