Method with null as arg

[Shubha Kirani]

In the below code, compiler error with message 'method is ambiguous'.

If I comment the method with StringBuffer as argument it compiles and gives "Object" as output. Can somebody explain why this happen ?

  
public class Test{
 
    static void method(String str){
        System.out.println("String");
    }
    static void method(Object obj){
        System.out.println("Object");
    }
    static void method(StringBuffer sb) {
    System.out.println("StringBuffer");
    }
    public static void main(String args[]){
        method(null);
    }
}

[Anupam Sinha]

Even if you comment the method that takes in a String argument it would work. The reason is that null is a valid argument for Object, String and StringBuffer. But the method with closest match is chosen over other methods for execution. Now when we have methods that accept Object type and String type of argument. String is more specific so the compiler knows that String method should be used. But when you have two or more completely different things(no where related in the class hierarchy) as the argumnet it is impossible for the compiler to determine which method should be called. Hence the error.

[Manfred Klug]

Originally posted by Anupam Sinha:
But when you have two or more completely different things(no where related in the class hierarchy) as the argumnet it is impossible for the compiler to determine which method should be called. Hence the error.

Even if the classes are related in the class hierarchy, it may be impossible for the compiler to decide which function should be called.

public class Test{
 
    static void method(Long longValue){
        System.out.println("Long");
    }
    static void method(Integer integer){
        System.out.println("Integer");
    }
    static void method(Number number) {
    System.out.println("Number");
    }
    public static void main(String args[]){
        method(null);
    }
}

[Shubha Kirani]

Thanks Anupam and Manfred for your replies. I'm understanding Java better now.