What does “The constructor … is ambiguous” mean?

Question

I would like to know what the error message in Eclipse means:

The constructor Case(Problem, Solution, double, CaseSource) is ambiguous

Answer 1

To add on to other answers, it can be avoided by casting the argument to what is intended, e.g.:

class Foo {

    public Foo(String bar) {}
    public Foo(Integer bar) {}

    public static void main(String[] args) {
        new Foo((String) null);
    }

}