Question

Is there any performance difference between using int a=a+1 and a++ in Java?

If so which is better and why? Could you briefly explain me to understand this?

Answer 1

Looking at the generated bytecode:

public static void main(String[] args) {
    int x = 1;
    int y = 1;
    int z = 1;
    int a = 1;
    int b = 1;
    x = x + 1;
    y++;
    ++z;
    a += 1;
    b += 2;
}

generates (use javap -c classname)

0:   iconst_1
1:   istore_1
2:   iconst_1
3:   istore_2
4:   iconst_1
5:   istore_3
6:   iconst_1
7:   istore  4
9:   iconst_1
10:  istore  5
12:  iload_1
13:  iconst_1
14:  iadd
15:  istore_1
16:  iinc    2, 1
19:  iinc    3, 1
22:  iinc    4, 1
25:  iinc    5, 2
28:  return

So using (jdk1.6.0_18):

x = x + 1

creates

12:  iload_1
13:  iconst_1
14:  iadd
15:  istore_1

whereas

y++;
++z;
a += 1;

all result in

iinc

However, doing a rough performance test on my laptop resulted in next to no difference in the runtime between the two (sometimes ++x was quicker, sometimes x=x+1 was quicker), so I wouldn’t worry about the performance implications.