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

The problem exists when you try to instantiate a class that could apply to more than one constructor.

For example:

public Example(String name) {     this.name = name; }  public Example(SomeOther other) {     this.other = other; }  

If you call the constructor with a String object, there's one definite constructor. However, if you instantiate new Example(null) then it could apply to either and is therefore ambiguous.

The same can apply to methods with similar signatures.

Answer 2

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);     }  }