How does this code works ?

[podonga poron]

public class NewClass {
public static void main(String [] args) {
boolean x = true;
boolean y = false;
short z = 42;

if((x = false) || (y = true)) z++; // Why gives 43 !?
if((z++ == 44) || (++z == 45)) z++; // Why gives 46 !?

System.out.println("z = " + z);
}
}

How does this code works ?

[Roger Chung-Wee]

if((x = false) || (y = true)) z++; // Why gives 43 !?

When you have a conditional OR operator where only one of the operands is true, then true is returned. So:

false || true returns true.

[marc weber]

Originally posted by podonga poron:
...
if((x = false) || (y = true)) z++; // Why gives 43 !?
if((z++ == 44) || (++z == 45)) z++; // Why gives 46 !?
...

There are quite a few details here. Which parts are you questioning?

If you tell us how you expected this to work, then we can help you find the problem.

[podonga poron]

i taked the code from the online practice certification for SUN java programer ..

they gives 4 options, and "z=46" is the one, but i don't understand how it arrives to that result ...

     boolean x = true;
     boolean y = false;
     short z = 42;
 
    if((x = false) || (y = true))  z++; // one statement is true so z=43
    if((z++ == 44) || (++z == 45)) z++; // and here ? what it does ?
 
      System.out.println("z = " + z);

BTW, what is the difference betwen ++z and z++ ?

thanks !

OT: what means i += 5 ?

[ May 23, 2008: Message edited by: podonga poron ]
[ May 23, 2008: Message edited by: podonga poron ]

[Jesper de Jong]

++z is pre-increment: it adds 1 to the variable z, and the result of the expression is the new value of z.

z++ is post-increment: it adds 1 to the variable z, and the result of the expression is the old value of z.

i += 5 is a short way to write i = i + 5.

[marc weber]

In this code, you might also note that || is a short-circuiting version of |, and that = is an assignment rather than the comparison operator ==.

But again, I think it would help if you posted your understanding of what this code does so that we know how to help you.

[Rob Spoor]

Originally posted by marc weber:
and that = is an assignment rather than the comparison operator ==.

Exactly. While you might think it is testing whether or not x is false, it is assigning false to x, then evaluating only x.

While in this case it won't matter that much (x == false is false since x is true; x = false will assign false and then evaluate to false), there are cases where it will:

boolean x = false;
if (x = true) z++;

While comparison will return false, the assignment will cause it to return true, and therefore z will be increased.