Question

Are these comparisons always safe from creating a NullPointer Exception ?

if( myObject == null || myObject.someMethod() == someValue )
{
    if( myObject == null && myObject.getAlwaysTrue() )
       {

       }
}

Is there some directional precedence in java for condition evaluation, apart from short circuiting ?

UPDATE: I Know myObject.anything() will throw a NullPointer. Its just that I have come across such code by other programmers, and I want to know if there’s a safe way of squeezing multiple checks along with a null check in a single condition. I’m looking for a good rule to stick to.

Answer 1

No, this line is not safe:

if( myObject == null && myObject.getAlwaysTrue() )

If you know that myObject is null then you shouldn’t try to dereference it. If however you wrote this:

if( myObject != null && myObject.getAlwaysTrue() )

Then it would be safe. This is because && (and || for that matter) has short-circuit evaluation. If you write a && b and the expression a evaluates to false, then the expression b is not evaluated so it will not throw an exception. The left operand is always evaluated first.