short-circuit question

[Grady Jamyson]

class EBH202 {
  static boolean a, b, c;
  public static void main (String[] args) {
    boolean x = (a = true) || (b = true) && (c = true);
    System.out.print(a + "," + b + "," + c);
}}

I think,

1) a = true is evaluated, so a = true
2) b = true is not evaluated, so b = false (short-circuit)
3) the original expresion would be, boolean x = true && (c = true)
4) c = true is evaluated, so c = true
5) boolean x = true

But the answer is, a = true, b = false, c = false
Any ideas?
Thanks a lot.

[Kitty Dayal]

Hey Grady,

It actually works this way.

op1 || op2 where op1, op2 are two operands.

if op1 is "true" then op2 will not be evaluated, EVEN IF op2 is an expression (in this case (b=true) && (c=true)).
Similarly for &&, if op1 is false then op2 is not evaluated at all.

One more point to note is both ||, && have same level of precedence and so if they appear in a expression, they will be evaluated as usually (from left-right).

Say,

if( false||true&&true||false )
   System.out.println( "check precedence" );

Here it will be evaluated as (false || (true && (true || false))) and so will print "check precedence".

Hope that was helpfull,
Kits

[Kapil Hingu]

Hi Grady,

If you look at operator precedence order of || and &&, && has the higher precedence than operator ||.
And also if you remember java always evaluates left oprand first for binary operators.
So the expression will get evaluated as -

boolean x = (a = true) || (b = true) && (c = true);//Original expression.

x = ((a = true) || ((b = true) && (c = true)));//According to the precedence.

x = (true || ((b = true) && (c = true)));//Left oprand evaluated first.

At this point sencond expression i.e ((b = true) && (c = true)) will never get evaluated as has got short circuited.

Hence the result is,

x = true; with a = true , b = false & c = false.

I hope this answers your question and not adding any confusion
Correct me if my understanding is wrong!

Regards,
Kapil

[Grady Jamyson]

Thank you, guys.
I'm quite clear how it works after you two explained.