Which one gives me better performance in variables declaration?

Question

I need to know which one of the following examples gives me higher performance?

Object O = someValue;
if (condition){
    //statements
    //statements
} else {
    //statements
    //statements
}

Or

Object O;
if (condition){
    O = someValue;
    //statements
    //statements
} else {
    O = someValue;
    //statements
    //statements
}

Or

if (condition){
    Object O = someValue;
    //statements
    //statements
} else {
    Object O = someValue;
    //statements
    //statements
}

NOTE: someValue is equal in all cases

Based on the code provided, unless you are using a computer that was built in the 80's, I don't think you should be worrying about such micro-optimizations. — Chetan Kinger, Jan 10 '17 at 07:45
@CKing No that's not what I'm writing this is just an example, I'm using this in a heavy algorithm and I need to know which one of these gives higher performance — Abd-Elrahman Adel, Jan 10 '17 at 07:52
It's worth noting that the third way changes the scope of the variable, which may be a good thing or a bad thing, depending. — D M, Jan 10 '17 at 17:08

score 3 · Accepted Answer · answered Jan 10 '17 at 08:03

Compilers are smart enough to analyze and identify the best way to initialize. But as a coding practice, first one would be preferred and below are the downsides of second and third.

Second way just increases the lines of code. If you need to modify the someValue in future, you (or someone who maintains the code) need to modify in two places. If the if block is long enough, we might miss out modifying the else block causing error situations.

Third way just initializes the variable inside the conditional blocks and are accessible only inside the blocks. To my understanding, even compiler might not optimize the initialization by moving it out of the conditional statements. This again suffers from problem of second approach. Also, the variables initialized within the conditional blocks are not accessible outside, so if you need to print / log the object outside the if/else block, its not allowed.

One more fact: Java coding conventions do not recommend using variable names beginning with a capital character.

score 1 · Answer 2 · answered Jan 10 '17 at 07:49

1

The first representation would be most optimal. That said, most modern compilers including JavaC optimizes the byte code to reduce or eliminate unnecessary initialization. You can check this with tools like javap or your favorite bytecode analyzer.

This applies to most compilers, not just Java.

answered Jan 10 '17 at 07:49

Aditya Sundaramurthy

61
3

Does this means that the compiler itself recognizes the best way to initialize the variables? – Abd-Elrahman Adel Jan 10 '17 at 07:56
Listing 2 basically assigns the same values to a reference. The compiler recognizes this as redundant and inlines the statement. Listing 3 is duplicating a reference in a local scope. Unless O is used within the scope, the compiler just eliminates it. – Aditya Sundaramurthy Jan 10 '17 at 08:01

Which one gives me better performance in variables declaration?

2 Answers2