Question

Inside of Java’s ByteBuffer is the method compareTo for implementing Comparable<ByteBuffer>…

public int compareTo(ByteBuffer that) {
    int n = this.position() + Math.min(this.remaining(), that.remaining());
    for (int i = this.position(), j = that.position(); i < n; i++, j++) {
        byte v1 = this.get(i);
        byte v2 = that.get(j);
        if (v1 == v2)
            continue;
        if ((v1 != v1) && (v2 != v2)) // For float and double
            continue;
        if (v1 < v2)
            return -1;
        return +1;
    }
    return this.remaining() - that.remaining();
}

What is the point of if ((v1 != v1) && (v2 != v2)) // For float and double?

If I write this kind of code, I’m warned about comparing identical expressions.

Answer 1

Double.NaN == Double.NaN and Float.NaN == Float.NaN gives false.

See also end of JLS 4.2.3:

The equality operator == returns false if either operand is NaN, and the inequality operator != returns true if either operand is NaN (§15.21.1).