java operator ++ problem

Question

I wonder why first code output is 000 while the second one is 123

first one:

int z=0;
    while(z<4)
    {
       z=z++;
       System.out.print(z);

    }

second one :

int z=0;
int x=0;
    while(z<5)
    {
       x=z++;
       System.out.print(x);

    }

what is the different between these two codes , why the first block do not increase the value of the z ?

Answer 1

Remember this, Java evaluates your expressions right to left (just like C and C++),

So if your code reads

z = z++

then if z is 0 before this line is executed, what happens is:

1. z++ is evaluated as an expression, returning the value 0
2. Then z is incremented because of the ++ operator, and it has the value 1.
3. Now the z on the left is assigned a value z = (value returned by z++)
4. Since the value returned by z++ was 0, z is reset to 0.

The important thing to note is that the result of the assignment inherent in z++ is evaluated before the z variable on the left is updated.