doubt related to "++" operator

[Sowjanya Chowdary]

Hi everybody,
i had just started preparing for scjp1.4
Please clear my doubt in the following code:

class abc {
public static void main (String[] args) {
int i=10;

i=i++; //(1)
System.out.println(i);
}
}

The program is printing 10.
Why is it so, eventhough 'i' is getting post incremented at (1).
Thanks for the help.

[madhup narain]

good question.... im wondering... and looking for a good answer..

[Patrick van Zandbeek]

good question

apparantly the ++ gets lost when you assign it to the same variable.
If you make an extra variable, j for instance and then say
j=i++;

j would be 10 and i would be 11 when printing after that.
Apparantly in i=i++; the ++ gets skipped after assigning i to i.

Having said that, i=i++ isn't what you want to be coding.
If you need to increment i just say i++; not i=i++;
or possibly i=i+1; if you can't live without an = sign.

Perhaps someone can explain more technically what happens during i+i++; but as far as I'm concerned, the bottom line is that you shouldn't write your code like that anyway.

[David Ulicny]

use just
i++;
or
i=++i;

[Sowjanya Chowdary]

This was my first question to java ranch.
Happy to see prompt replies.

Even though i know it is better to write i++ rather than i=i++ , i just wanted to know the reason of strange behavior.
Thanks once again.

[Arun Kumarr]

LHS= left hand side.
RHS= right hand side.

when you say,
i=10;
i = i++;

i(RHS) is incremented to 11 and the old value (10) is remembered and set to i(LHS);


when you say,

i=10;
i=++i;

i(RHS) is incremented to 11 and then i(LHS) is set to 11.

[Joanne Neal]

Originally posted by Amrutha Ch:
This was my first question to java ranch.
Happy to see prompt replies.

As you are new to Javaranch, you should read this. A quick search would have revealed this question has been asked many times, even in the short time I've been coming here.

[Niyas Ahmed Sheikh]

I have some doubts regd this post:

class increment
{
   public static void main(String args[])
   {
       int i = 10;
       i = i++;
       System.out.println(i);  
   }
}
Output:
10

class increment
{
   public static void main(String args[])
   {
       int i = 10;
       i = i++;
       int j = i++;
       System.out.println(i);  
       System.out.println(j);  
   }
}
Output:
11
10
[B]How????????[/B]

class increment
{
   public static void main(String args[])
   {
       int i = 10;
       i = ++i;
       System.out.println(i);  
   }
}
Output:
11

class increment
{
   public static void main(String args[])
   {
       int i = 10;
       i = i++ + ++i;
       int j = i++;
       System.out.println(i);  
       System.out.println(j);  
   }
}
Output:
22
[B]How?????[/B]

[Ilja Preuss]

Originally posted by Niyas Ahmed Sheikh:
I have some doubts regd this post:

What do you think it *should* print, and why?

[Niyas Ahmed Sheikh]

class increment
{   
  public static void main(String args[])    
  {
      int i = 10;       
      i = i++ + ++i;   // i = i++(10) + ++i(11) = 21, how comes 22    
      System.out.println(i);         
   }
}

[fred rosenberger]

you forget that the pre-increment operator acts first. so, the first thing that happens is i is incremented to 11.

then, you add i + i, to get 22. i is then post incremented to 12.

22 is then assigned to i.

print 22.