Local variables: Programming Practices

Question

Given the following methods:

public int methodOne() {
    int total = local_int_one + local_int_two;
    return total;
}

public int methodTwo() {
    return local_int_one + local_int_two;
}

1) Is the only difference in the above methods readability or is there a micro-optimization "benefit" in methodTwo()?

2) Should the defining of local variables in a narrow scope be shunned and avoided when possible? (I can see methodTwo becoming unreadable if several calculations must be performed in a single statement)

Answer 1

The short answer is: methodTwo() is slightly more efficient.

methodOne() results in the following bytecode:

public int methodOne();
 0  aload_0 [this]
 1  getfield com.example.Test.local_int_one : int [13]
 4  aload_0 [this]
 5  getfield com.example.Test.local_int_two : int [15]
 8  iadd
 9  istore_1 [total]
10  iload_1 [total]
11  ireturn

And here's the bytecode for methodTwo():

public int methodTwo();
 0  aload_0 [this]
 1  getfield com.example.Test.local_int_one : int [13]
 4  aload_0 [this]
 5  getfield com.example.Test.local_int_two : int [15]
 8  iadd
 9  ireturn

But note that this optimization is too minor, and that code readability in this case matters a lot more then a couple of java instructions.

If you think a temporary variable will contribute to code readability, then, by all means, use it.