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javaconditional-operatorshort-circuiting
Mike Pone
Mike Pone

Reputation: 19330

Java ternary (immediate if) evaluation

I can't find the relevant portion of the spec to answer this. In a conditional operator statement in Java, are both the true and false arguments evaluated?

So could the following throw a NullPointerException 

Integer test = null;

test != null ? test.intValue() : 0;

Upvotes: 35

Views: 25399

Answers (3)

Michał Króliczek
Michał Króliczek

Reputation: 1339

I know it is old post, but look at very similar case and then vote me :P

Answering original question : only one operand is evaluated BUT:

@Test
public void test()
{
    Integer A = null;
    Integer B = null;

    Integer chosenInteger = A != null ? A.intValue() : B;    
}

This test will throw NullPointerException always and in this case IF statemat is not equivalent to ?: operator.

The reason is here http://docs.oracle.com/javase/specs/jls/se5.0/html/expressions.html#15.25. The part about boxing/unboxing is embroiled, but it can be easy understood looking at:

"If one of the second and third operands is of type boolean and the type of the other is of type Boolean, then the type of the conditional expression is boolean."

The same applies to Integer.intValue()

Best regards!

Upvotes: 25

Michael Myers
Michael Myers

Reputation: 192015

Since you wanted the spec, here it is (from §15.25 Conditional Operator ? :, the last sentence of the section):

The operand expression not chosen is not evaluated for that particular evaluation of the conditional expression.

Upvotes: 63

stevedbrown
stevedbrown

Reputation: 8934

No, it couldn't. That's the same as:

Integer test = null;
if ( test != null ) { 
    test = test.intValue();
}
else {
    test = 0;
}

Upvotes: 8

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