Same output for postincrement and preincrement in a for loop

Question

These are two java programs on a postincrement and preincrement operators being used on a for loop .both produces the same output.Then what is the difference between using preincrement and postincrement operators on a for loop.

public class Printi{
public static void main(String args[])
  {
  int i=0;
  for(i=0;i<5;++i){
  System.out.println(i);
  }

  }
}

produces output

C:\fx>java Printi
0
1
2
3
4

And this postincrement operator in for loop also produces same output

public class Printj{
public static void main(String args[])
  {
  int j=0;
  for(j=0;j<5;j++){
  System.out.println(j);
  }

  }
}

C:\fx>java Printj
0
1
2
3
4

In a for loop there is no difference between the use of either, in terms of using them... I see programmers use both interchangeably! — Ryan Turnbull, Nov 12 '15 at 05:42

score 0 · Answer 1 · answered Nov 12 '15 at 05:24

Yes (because you aren't displaying the value returned by the increment expression). To see the difference, compare

for(int j=0;j<5;){
    System.out.println(j++);
}

and

for(int j=0;j<5;){
    System.out.println(++j);
}

All three parts of the for loop syntax are optional.

score 0 · Answer 2 · answered Nov 12 '15 at 05:30

In a for loop, the way you've structured it, there is no difference. By the time the "j" is printed out inside of the loop, it has already been either pre or post evaluated.

The only interesting time about pre or post evaluation is right when you actually apply that evaluation to the variable, which is what @Elliot Frish is showing in his answer.

After the evaluation, the code rightfully wont see a difference.

Something like that might make more of a difference when you structure it inside of a while loop.

score 0 · Answer 3 · answered Nov 12 '15 at 05:30

The only difference between x++ and ++x can only be shown in a statement with many operators and operands.

Consider this:

int x = 10;
int y = ++x;

x is first incremented by the prefix ++. And then the incremented x is assigned to y. So after this code, x = 11 and y = 11.

If I change this to:

int x = 10;
int y = x++;

x is assigned y first because the suffix ++ is executed last. After x is assigned to y, x gets incremented. So after this code, x = 11 and y = 10.

That's the difference. In your example, you only have one operation: ++x. Because there is only one, you cannot show the order of the operations!

Same output for postincrement and preincrement in a for loop

3 Answers3