Increment Operator

[Sivakumar Nachimuthu]

class TrickyTest {

public static void main ( String args [ ] ) {
int i = 10 ; // line 1
i = ++i ; // line 2
i = i++ ; // line 3
System . out . println ( i ); // line 4
}
};

It prints 11. In line 3 , why the increment did not happen?

[wise owen]

PostIncrementOperatorAndAssignment .

[Somesh Rathi]

Please find the following explaination from this post in javaranh
refer to this post

In a normal situation (like in j = k++) this is what happens:
A.The current value of k is stored temporarily in the stack.
B.The value of k is incremented
C.The value on the stack is assigned to j


This is how it happens in this abnormal situation ( j = j++)
A.The current value of j is stored temporarily in the stack.
B.The value of j is incremented
C.The value on the stack is assigned to j

Hope this would clear your doubt
Regards,
Somesh

[ming ming]

can I say that "i" is assign before the increment operator,so that's why "i" automatic assign the value of before increment.

[Naseem Khan]

Hi,
Still its not clear.

int k = 0, i=0;
for(int x=0; x < 5; x++){   
  i = k++;
}
System.out.println(i);

This prints 4.

int k = 0, i=0;
for(int x=0; x < 5; x++){   
  i = i++;
}
System.out.println(i);

This prints 0.

On javaranch faq its mentioned that....

"i++" is evaluated. The value of "i++" is the value of i before the increment happens.
As part of the evaluation of "i++", i is incremented by one. Now i has the value of 1;
The assignment is executed. i is assigned the value of "i++", which is the value of i before the increment - that is, 0.

Now I think its a bug in java in that it behaves differently for i=i++; and i=j++;

On java sun site here Definite Assignment

Its mentioned....

1. V is definitely assigned after ++a, --a, a++, or a-- iff either a is V or V is definitely assigned after the operand expression.

2. V is definitely unassigned after ++a, --a, a++, or a-- iff a is not V and V is definitely unassigned after the operand expression.
3. V is [un]assigned before a iff V is [un]assigned before ++a, --a, a++, or a--.


regards

Naseem

[Christophe Verré]

Now I think its a bug in java in that it behaves differently for i=i++; and i=j++;

Do you seriously think that this would be a bug ?

i++ return the value of i before the incrementation.
So after i=i++, i still has the same value, always.
So looping 5 times won't make it change.

k++ returns the value k before the incrementation.
But you're not assigning k to itself.
So after i = k++, i and k both change.

This is not a bug, it's logic

[Jotnarta Jot]

Originally posted by Sivakumar Nachimuthu:
class TrickyTest {

public static void main ( String args [ ] ) {
int i = 10 ; // line 1
i = ++i ; // line 2
i = i++ ; // line 3
System . out . println ( i ); // line 4
}
};

It prints 11. In line 3 , why the increment did not happen?

Java evaluates its expressions left to right. so, in line2, the variable i first incremented then assigned to i.

in line 3, the old value of i will be replaced with produced value from line2, and that happenes before incrementing.

[Naseem Khan]

Now I got it.
Thanks to all...

int i=0;
for(int x=1;x<5;x++){
  i=i++;
}

i++ is the value of i before increment happens.

First i++ get evaluated which is equivalent to i=i+1; so i becomes 1.
i=value of i before increment happens. // from above quote so i becomes 0.

int i=0, j=0;
for(int x=1;x<5;x++){
  j=i++;
}

This is how code works...

1. First i++ get evaluated which is equivalent to i=i+1; so i becomes 1.
j=value of i before increment happens. // from above quote so j becomes 0.

2. Second time. i++ get evaluated which is equivalent to i=i+1; so i becomes 2.
j=value of i before increment happens. // from above quote so j becomes 1.

3. Third time. i++ get evaluated which is equivalent to i=i+1; so i
becomes 3.
j=value of i before increment happens. // from above quote so j becomes 2.

4. Fourth time. i++ get evaluated which is equivalent to i=i+1; so i
becomes 4 now.
j=value of i before increment happens. // from above quote so j becomes 3.

Thanks & Regards


Naseem Khan
[ May 18, 2006: Message edited by: Naseem Khan ]