Guarantee of order of conditions in if statement?

Question

Given that example code:

boolean foo(String arg)
{
    if( arg != null && arg.equalsIgnoreCase("bar") )
        //Do something
}

Do I have guarantee that equalsIgnoreCase() is only called if arg is not null ?

Yes. That's exactly what `&&` was designed for (in C). Similarly `||`. — ajb, Apr 18 '14 at 16:14

score 3 · Accepted Answer · answered Apr 18 '14 at 16:11

Yes, Java does offer short-cicuiting for conditionals, operating from left to right.

JLS states:

The conditional-and operator && is like & (§15.22.2), but evaluates its right-hand operand only if the value of its left-hand operand is true.

If the resulting value is false, the value of the conditional-and expression is false and the right-hand operand expression is not evaluated.

If the value of the left-hand operand is true, then the right-hand expression is evaluated; if the result has type Boolean, it is subjected to unboxing conversion (§5.1.8). The resulting value becomes the value of the conditional-and expression.

score 1 · Answer 2 · edited Jun 20 '20 at 09:12

Yes, Java will guarantee that equalsIgnoreCase is only called if arg is not null. It will evaluate its operands from left to right, and in the case of && (and ||), it will not evaluate the right operand if it doesn't need to evaluate it.

Section 15.23 of the JLS states:

The conditional-and operator && is like & (§15.22.2), but evaluates its right-hand operand only if the value of its left-hand operand is true.

and

At run time, the left-hand operand expression is evaluated first; if the result has type Boolean, it is subjected to unboxing conversion (§5.1.8).

If the resulting value is false, the value of the conditional-and expression is false and the right-hand operand expression is not evaluated.

Guarantee of order of conditions in if statement?

2 Answers2