What function is more efficient?

Question

I'm new to Java and i wanted to know if there is a difference between these 2 functions:

public static String function1(int x) {
    String res = "";
    if(x > 10)
        res = "a";
    else
        res = "b";

    return res;
}

and:

public static String function2(int x) {
    if(x > 10)
        return "a";

    return "b";
}

and I'm not speaking on the length of the code, only efficiency.

In _theory_, version 2 is more efficient, but in practise it should be negligible. — Alnitak, Mar 28 '18 at 16:02
I think the second one is more efficient since it avoid to allocate memory for a variable, affect it and then read it. But maybe the compiler is able to detect that res is useless and compile the same for both solution — vincrichaud, Mar 28 '18 at 16:03
what about static String function2(int x) { return x > 10 ? "a" : "b";} — RAZ_Muh_Taz, Mar 28 '18 at 16:05
function2 is more efficient, check on one condition and have no variables. but the code is simple compiler can't notice the difference. — Zeyad Etman, Mar 28 '18 at 16:06
An `else` is not a "condition", it's just the code that's executed when the `if` branch isn't taken. — Alnitak, Mar 28 '18 at 16:23
One could argue this is a duplicate of [How do I write a correct micro-benchmark in Java?](https://stackoverflow.com/q/504103) — Bernhard Barker, Mar 28 '18 at 16:31

Alnitak · Answer 1 · 2018-03-28T16:21:56.990

The second version is in theory more efficient, decompiling to:

public static java.lang.String function1(int);
Code:
   0: ldc           #2                  // String
   2: astore_1
   3: iload_0
   4: bipush        10
   6: if_icmple     12
   9: ldc           #3                  // String a
  11: areturn
  12: ldc           #4                  // String b
  14: areturn

whereas the version with the assignment decompiles to:

public static java.lang.String function1(int);
Code:
   0: ldc           #2                  // String
   2: astore_1
   3: iload_0
   4: bipush        10
   6: if_icmple     15
   9: ldc           #3                  // String a
  11: astore_1
  12: goto          18
  15: ldc           #4                  // String b
  17: astore_1
  18: aload_1
  19: areturn

where it can be seen that the additional variable is created and returned.

However in practise the difference in actual runtime performance should be negligible. The JIT compiler would (hopefully) optimise away the useless variable, and in any case unless the code was in a hot code path according to your profiler then this would certainly count as premature optimisation.

I was just writing this exact answer. For the benefit of the OP, the bytecode was obtained by compiling a class containing these methods using `javac ClassName.java` then running `javap -c ClassName`. — bcsb1001, Mar 28 '18 at 16:13

hoan · Answer 2 · 2018-03-28T16:15:07.317

0

Both versions end up creating a string either "a" or "b" and return it out. But version 2 is better in term of efficiency, which doesn't create an redundant empty string "" in memory.

edited Mar 28 '18 at 16:15

answered Mar 28 '18 at 16:05

hoan

1,058
8
13

`""` is interned (as a string literal), so no redundant empty string will be actually created. – lexicore Mar 28 '18 at 16:07
1

@lexicore The code will add the empty string to the intern pool, so it *is* created by the code. – Andreas Mar 28 '18 at 16:11

What function is more efficient?

2 Answers2