Rules for post-increment and pre-increment operations in java

Question

Oh, I've something missed with this example...

int a=1;
int b=1;
int c=1;
System.out.println(a+++b---c++);

Is not it the same as next?

System.out.println( (a++) + (b--) - (c++) );

It seems the result is 0, but that's definitely wrong, so what's going on here?

Answer is 1 only http://ideone.com/0DleI4 – Harish Nov 08 '15 at 08:59 — Harish, Nov 08 '15 at 08:59

score 1 · Accepted Answer · answered Nov 08 '15 at 08:59

I get 1 (and that's what I expect, 1 + 1 - 1 is 1). Using the eclipse indenter (and adding output for a b and c after the operation)

int a = 1;
int b = 1;
int c = 1;
System.out.println(a++ + b-- - c++);
System.out.printf("a=%d b=%d c=%d%n", a, b, c);

I see

1
a=2 b=0 c=2

And, the reason is that post increment doesn't take effect until the next statement. While pre increment (for example, ++a) takes effect immediately.

score 0 · Answer 2 · answered Nov 08 '15 at 09:11

By using debugger i watch all variables for following to expression

a=b=c=1

A. a++ + b-- - c++ = 1 + 1- 1 =0

After A => a=2 b=0 c=2

B. (a++) + (b--) - (c++) = 2 + 0 - 2

After B=> a=3 b=-1 c=3

There is no difference between a++ + b-- - c++ and (a++) + (b--) - (c++) when we execute these expression in different class there is same result for same input.

Rules for post-increment and pre-increment operations in java

2 Answers2