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postincrement operator ++

 
Greenhorn
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my question is as follows,

public class Inc{
public static void main(String argv[]){
Inc inc = new Inc();
int i =0;
inc.fermin(i);
i = i++;
System.out.println(i);
}
void fermin(int i){
i++;
}
}
ANS)1 Compile time error
2 Output of 2
3 Output of 1
4 Output of 0

The Correct Answer is
4) Output of 0

Explaination:
The method fermin only receives a copy of the variable i and any modifications to it are not reflected in the version in the calling method. The postincrement operator ++ effectively modifies the value of i after the initial value has been assigned to the left hand side of the equals operator. This can be a very tricky concept to understand

why does any modification done don't reflect the method?
and why the value assigned by the post increment don't affect i variable?

please kindly guide me, i have not understood the above topic.
thank you,
trupti
 
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why does any modification done don't reflect the method?



It did, but the local variable went out of scope when the method ended. If you print the value prior to returning from the method, you will see that the parameter variable did change.

and why the value assigned by the post increment don't affect i variable?



This is a common question... that it is actually in the JavaRanch FAQ.

http://faq.javaranch.com/java/PostIncrementOperatorAndAssignment

Henry
 
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Hi,
Try to use the code blocks, so that the indentation isn't lost and the code is clearer.
I'm not sure what you mean in your first question. If you're asking why the variable remains unchanged after calling fermin(), it is because the method only gets a copy of the variable you pass as argument. Once in the method, the parameter is much like a local variable, it has no effect on the outside world. If instead of a primitive the argument was an object, this would still be true, however the "object" is a reference to an object, and then the method would be handling the same actual object that is referenced outside the method. That is, the method takes only a copy of the reference, but this reference points to the same object that the reference passed by argument.

The i = i++ part is tricky indeed; I would have guessed the program outputs 1, but no, it prints 0 and I don't get it. The explanation says that the value of i actually changes after being assigned to the left operand, so...

Edit: Thanks Henry for the FAQ reference.
[ September 22, 2007: Message edited by: greg buela ]
 
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