What is the level of optimization of the java compiler?

Question

So lets consider this following statement that executes more than a million times inside a loop.

boolean validity = condition1 || condition2;

It is safe to assume that both condition1 and condition2 have very complex calculation inside them. So since there is an OR operator here, I assume it would be wise to separately check for condition1 first and then if necessary, condition2 afterwards like,

boolean validity = condition1;
if( !validity )
    validity = condition2;

Should I manually perform optimizations like this or does the java compiler automatically takes care of these things?

OR operation will never check condition2 if condition1 is true. — Ankush soni
– Ankush soni, Commented Oct 13, 2015 at 7:44

Tagir Valeev · Accepted Answer · 2015-10-13 07:50:16Z

8

As Java Language Specification, §15.24 says:

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

Thus it's required by language specification that the right part is evalutated only if left part is false. It's not an optimization, it's a part of language. Optimizations are not the part of language specification, they may make your code faster, but they should never make your code to behave differently. Here however the behavior would be different if both parts were evaluated as the right part might have a side-effect.

edited Oct 13, 2015 at 7:50

answered Oct 13, 2015 at 7:44

Tagir Valeev

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2 Comments

Kiran Over a year ago

Thanks for the answer Tagir. So are there any cases where an eager operation is preferred over a short circuit one?

Tagir Valeev Over a year ago

@KiranR, actually I don't know such cases. FindBugs tries to report when non-short-circuit boolean expressions are detected and I don't remember that anybody complained that such report is false-positive (I'm a FindBugs contributor). Probably it was added in Java 1.0 just to be closer to C... Of course | for int/long type is very useful, but not for boolean.

Robert Franz · Accepted Answer · 2015-10-13 07:43:32Z

-1

The java compiler is capable to execute the function for condition1 at first. When it is true then the function for condition2 is not executed any longer. So the optimization is not required. This is as there is an OR-Operation.

answered Oct 13, 2015 at 7:43

Robert Franz

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1 Comment

Robert Franz Over a year ago

apparently you didn't read the answer. compared to the other I wrote exactly the same. But without the reference to the spec.

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