Can someone explain this output in java?

Question

I ran the following code snippet

int n=0;
for(int m=0;m<5;m++){
n=n++;
System.out.print(n)}

I got the output as 00000 when i expected 01234. Can someone explain why

Thanks in advance

Answer 1

n = n++ increments n , then sets n to the value it had before you incremented it. Use either:

n++;

or

n = n + 1;

but don't try to do both at once. It doesn't work.

Answer 2

n=n++; should be just n++; or n=n+1; (or even n=++n; if you want)

n++ does the increment but will return the value of n before the increment took place. So in this case you're incrementing n , but then setting n to be the value before the increment took place, effectively meaning n doesn't change.

The ++ operator can either be used as prefix or postfix. In postfix form ( n++ ) the expression evaluates to n , but in the prefix case ( ++n ) the expression will evaluate to n+1 . Just using them on their own has the same outcome though, in that n 's value will increment by 1.

Answer 3

When you have a ++, the operator can either be BEFORE or AFTER the variable. Likewise, the addition will occur before or after the operand is executed. If the line were to have read:

n = ++n;

Then it would have done what you would have expected it to do.

Answer 4

Since it doesn't seem to have been mentioned previously, you can also use

n += 1;

if you really like assignment operators.

Answer 5

n = ++n;

would also work :-) But it is useless to assign a variable to itself. In order to increment n, just use

n++;

or

++n;

Answer 6

Java uses value of a variable in the next instance on post increment.

In the code snippet, the loop execute for the first time picks up n=0 and increments at the operand. But the incremented value will be reflected on next occurrence of n not in current assignment hence 0 will be set to n one more time. I think this is because n=n++ is ATOMIC operation.

So the n is set 0 always.

To avoid this either you do pre-increment [++n] or +1 [n+1] where your reference get updated immediately.

Hope this answers your question.