Premature optimization in Java: when to use “x = foo.getX()” vs simply “foo.getX()”

Question

When I find myself calling the same getter method multiple times, should this be considered a problem? Is it better to [always] assign to a local variable and call only once?

Answer 1

Two things have to be considered:

1. Does the call to getX() have any side effects? Following established coding patterns, a getter should not alter the object on which it is called, the in most cases, there is no side effect. Therefore, it is semantically equivalent to call the getter once and store the value locally vs. calling the getter multiple times. (This concept is called idempotency - it does not matter whether you call a method once or multiple times; the effect on the data is exactly the same.)

2. If the getter has no side effect, the compiler can safely remove subsequent calls to the getter and create the temporary local storage on its own - thus, the code remains ultra-readable and you have all the speed advantage from calling the getter only once. This is all the more important if the getter does not simply return a value but has to fetch/compute the value or runs some validations.

Assuming your getter does not change the object on which it operates it is probably more readable to have multiple calls to getX() - and thanks to the compiler you do not have to trade performance for readability and maintainability.