Thread: method always returns 0

public static int Count( ArrayList<Student> studentList )
{
int j = 0;
for( Student s : studentList )
{
j = j++;
}
return j;
}

What am I doing wrong?

Originally Posted by bdennin

... wrong...

Four common ways to increment the value of the variable j: in memory:

    j = j + 1;

    j += 1;

    j++;

    ++j;

Your statement in the loop is none of these. It is:

    j = j++;

This has the following effect:

Since the ++ operator has higher precedence than the '=' operator, it evaluates the expression on the right of the '=' first, then it stores the value of the expression in memory:

So, here's the drill:

• Evaluates the expression j++. The value of the expression is the previous value of the variable j in memory
  
  
• This particular expression has a side-effect: It increments the value of j in memory (after the expression has been evaluated) and, therefore, stores the incremented value in memory. At this point you have incremented the value of j
  
  However...
  
  
• Then, applying the '=' operator, it stores the previously obtained value of the expression in memory, thus overwriting the incremented value that you just stored, with the old value.

Bottom line: It stores the old value in memory each and every time.

You can easily verify my assertion by running something like the following:

public class Z {
    public static void main(String [] args) {
        int j = 0;
        for (int i = 0; i < 5; i++) {
            j = j++;
            System.out.printf("i = %d: j = %d\n", i, j);
        }
    }
}

Output::

i = 0: j = 0
i = 1: j = 0
i = 2: j = 0
i = 3: j = 0
i = 4: j = 0

Cheers!

Z