Undocumented String.compareTo(null) NPE?

Question

The following little test throws an NPE:

public class Test {

    public static void  main(String[] args) {

        String a = \"a\";
        String b = nul         


        

Answer 1

You can get some explanation when you look at the Comparable interface:

Note that null is not an instance of any class, and e.compareTo(null) should throw a NullPointerException even though e.equals(null) returns false.