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Question

Java operator to check if either conditions are false, but not both or none

Answer 1

+8 A:

You want XNOR, basically:

if (!(a ^ b))

or (more simply)

if (a == b)

where a and b are the conditions.

Sample code:

public class Test
{
    public static void main(String[] args)
    {
        xnor(false, false);
        xnor(false, true);
        xnor(true, false);
        xnor(true, true);
    }

    private static void xnor(boolean a, boolean b)
    {
        System.out.printf("xnor(%b, %b) = %b\n", a, b, a == b);
    }
}

Produces this truth table;

xnor(false, false) = true
xnor(false, true) = false
xnor(true, false) = false
xnor(true, true) = true

Jon Skeet 2010-01-11 15:57:18

Jon, it would probably be beneficial to show the full logic table for the XOR operator in this case. I would do it here, but the comment formatting is horrible for this.

jdmichal 2010-01-11 16:02:11

Thanks, that was what I was looking for! I knew there was an operator, just couldn't remember it :)

James 2010-01-11 16:02:17

@James: I've edited this with a simpler way of doing this - the equality operator!

Jon Skeet 2010-01-11 16:03:05

Also, yes, `!=` is simpler. But !XOR is the correct boolean operator for this case. So I still like your answer the best.

jdmichal 2010-01-11 16:04:10

That definition of xnor as !(A ^ B) looks a bit unusual, (A ^ B) v (!A ^ !B)

Andrew 2010-01-11 16:05:18

@jdmichal: != is actually wrong; that gives XOR instead of XNOR. @Andrew: I think of XNOR as the inverse of XOR, leading to that representation. It has the advantage of only evaluating each condition once...

Jon Skeet 2010-01-11 16:10:55

@Jon, running True,True through your expression though gives !(true and true) = false, unless you mean't something else in the ascii representation.

Andrew 2010-01-11 16:12:42

My quick-type errors aside, I still believe what I stated.

jdmichal 2010-01-11 16:30:39

@Andrew: I don't see what you mean. true ^ true is false, so !(true ^ true) is true. I never wrote "and". Could you clarify?

Jon Skeet 2010-01-11 17:08:23

Your ascii representation ^ is meaning something other than 'and', which would be the common interpretation of that symbol. Consequence of ascii vs logic symbols.

Andrew 2010-01-11 17:30:28

This question was given in the context of Java. In Java, the `^` symbol represents the bit-operation XOR.

jdmichal 2010-01-11 19:23:43

@Andrew: It's not an *ASCII* representation - it's code. It's an "if" condition, in the context of a Java question. I haven't used the symbol ^ anywhere other than in a code font, for a real snippet of code, in a question about coding.

Jon Skeet 2010-01-11 19:45:39

My mistake, I was reading it as a logical statement independant of a language. When I wrote the original comment, I put in XNor as it would be expressed in a mathematical statement.

Andrew 2010-01-11 19:54:53

Answer 2

A:

well if x and y are bools, you could just check:

boolean valid = x != y;

David Hedlund 2010-01-11 15:59:02

Wrong way round - it's XNOR which is required, not XOR.

Jon Skeet 2010-01-11 16:03:37

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Java operator to check if either conditions are false, but not both or none

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