Constructor is Ambiguous !!

What does it mean ?
         As the name, the compiler is confused between two constructors and do not know which one it should be using  to instantiate the class.

When does it occur ?
         When you have  - Overloaded Constructors
                                   - With the same number of parameters        

A Scenario
       
         class AmbiguousConstructor
        {
              public AmbiguousConstructor(String s, int i) { ... }
              public AmbiguousConstructor(ArrayList<Integer>, int i) { ... }
              ...
        }

    Now when we try to create the object
           
           AmbiguousConstructor ac= new AmbiguousConstructor(null,3);
           // Here the compiler says the constructor is ambiguous because null can be passed in the place of  both String and ArrayList.

How to avoid ambiguous constructor ?
          If you want to call the constructor with String parameter, just cast the null to the required type like
               AmbiguousConstructor((String) null, 3);