Question

Can Java’s == operator be asymmetric for primitive values, so that x == y, but y != x, where x and y are both variables of some (possibly different) primitive types?

Edit:

OK, I’ll be honest with the reason why I ask. In the Java Puzzlers book, there is this puzzle #87 which concerns the == operator for primitive types.

It has three parts, one challenges reader to find a case where the == operator is not reflective, second is for finding a case where == is not transitive. I’ve found solutions for both of them, but I have no idea how to solve the third one, which is defined like this:

public class Symmetric {
    public static void main(String[] args) throws Exception {
        /*
         * If you can come up with a set of primitive types and values
         * that causes this program to print "true false", then
         * you have proven that the == operator is not symmetric.
         */
        <typeX> x = <valueX>;
        <typeY> y = <valueY>;

        System.out.print ((x == y) + " ");
        System.out.println(y == x);
    }
}

I don’t own the book, so I cannot look it up for a solution, I only got across the source files, which don’t contain the solutions.

Answer 1

== Is symmetric for every type…

From the spec:

The equality operators are commutative if the operand expressions have no side
effects.