Creating a "logical exclusive or" operator in Java

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Observations:

Java has a logical AND operator.
Java has a logical OR operator.
Java has a logical NOT operator.

Problem:

Java has no logical XOR operator, according to sun. I would like to define one.

Method Definition:

As a method it is simply defined as follows:

public static boolean logicalXOR(boolean x, boolean y) {
    return ( ( x || y ) && ! ( x && y ) );
}


Method Call:

This method is called in the following way:

boolean myVal = logicalXOR(x, y);


Operator Usage:

I would much rather have an operator, used as follows:

boolean myVal = x ^^ y;


Question:

I can't find anything on how to go about defining a new operator in Java. Where should I start?

19 Answers

Java does have a logical XOR operator, it is ^ (as in a ^ b).

Apart from that, you can't define new operators in Java.

Edit: Here's an example:

public static void main(String[] args) {
    boolean[] all = { false, true };
    for (boolean a : all) {
        for (boolean b: all) {
            boolean c = a ^ b;
            System.out.println(a + " ^ " + b + " = " + c);
        }
    }
}

Output:

false ^ false = false
false ^ true = true
true ^ false = true
true ^ true = false

Java has a logical AND operator.
Java has a logical OR operator.

Wrong.

Java has

  • two logical AND operators: normal AND is & and short-circuit AND is &&, and
  • two logical OR operators: normal OR is | and short-circuit OR is ||.

XOR exists only as ^, because short-circuit evaluation is not possible.

Perhaps you misunderstood the difference between & and &&, | and || The purpose of the shortcut operators && and || is that the value of the first operand can determine the result and so the second operand doesn't need to be evaluated.

This is especially useful if the second operand would results in an error. e.g.

if (set == null || set.isEmpty())
// or
if (list != null && list.size() > 0)

However with XOR, you always have to evaluate the second operand to get the result so the only meaningful operation is ^.

That's because operator overloading is something they specifically left out of the language deliberately. They "cheated" a bit with string concatenation, but beyond that, such functionality doesn't exist.

(disclaimer: I haven't worked with the last 2 major releases of java, so if it's in now, I'll be very surprised)

The only operator overloading in Java is + on Strings (JLS 15.18.1 String Concatenation Operator +).

The community has been divided in 3 for years, 1/3 doesn't want it, 1/3 want it, and 1/3 doesn't care.

You can use unicode to create method names that are symbols... so if you have a symbol you want to use you could do myVal = x.$(y); where $ is the symbol and x is not a primitive... but that is going to be dodgy in some editors and is limiting since you cannot do it on a primitive.

What you're asking for wouldn't make much sense. Unless I'm incorrect you're suggesting that you want to use XOR to perform Logical operations the same way AND and OR do. Your provided code actually shows what I'm reffering to:

public static boolean logicalXOR(boolean x, boolean y) {
    return ( ( x || y ) && ! ( x && y ) );
}

Your function has boolean inputs, and when bitwise XOR is used on booleans the result is the same as the code you've provided. In other words, bitwise XOR is already efficient when comparing individual bits(booleans) or comparing the individual bits in larger values. To put this into context, in terms of binary values any non-zero value is TRUE and only ZERO is false.

So for XOR to be applied the same way Logical AND is applied, you would either only use binary values with just one bit(giving the same result and efficiency) or the binary value would have to be evaluated as a whole instead of per bit. In other words the expression ( 010 ^^ 110 ) = FALSE instead of ( 010 ^^ 110 ) = 100. This would remove most of the semantic meaning from the operation, and represents a logical test you shouldn't be using anyway.

This is an example of using XOR(^), from this answer

byte[] array_1 = new byte[] { 1, 0, 1, 0, 1, 1 };
byte[] array_2 = new byte[] { 1, 0, 0, 1, 0, 1 };

byte[] array_3 = new byte[6];

int i = 0;
for (byte b : array_1)
    array_3[i] = b ^ array_2[i++];

Output

0 0 1 1 1 0

Here's an example:

Given 2 int values, return true if one is negative and one is positive. Except if the parameter "negative" is true, then return true only if both are negative.

    public boolean posNeg(int a, int b, boolean negative) {
      if(!negative){
        return (a>0 && b<0)^(b>0 && a<0);
      }
      else return (a<0 && b<0);
    }

you'll need to switch to Scala to implement your own operators

pipe example

Can be achieved using stream API in java 8 and above

public static boolean logicalXOR(boolean x, boolean y) {  // can modify to take [] or list of bools
    return Stream.of(x, y)  // modify as per method params
        .filter(bool -> bool)
        .count() == 1;
}
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