Ambiguous method overloading

[Anil Deshpande]

Have look at the following code

 
public class Test1 {

	static public void method1(Object object)
	{
		System.out.println("Object");
	}
	
	static public void method1(String string)
	{
		System.out.println("String");
	}
	
	
	public static void main(String[] args) {
		
		method1(null);
	}
}
   

the out put it is showing in String.

why not object. Bacause Object can also be null

Please Clarify regarding this.

Thanks And Regards
Anil Deshpande

[Matthew Brown]

According to the Java language specification:

If more than one member method is both accessible and applicable to a method invocation ... The Java programming language uses the rule that the most specific method is chosen.

Because String is a subclass of Object, the version with String is considered more specific.

Try adding the following method:

static public void method1(Integer i)   {  
    System.out.println("Integer");  
}

What do you think will happen now?

[Anil Deshpande]

it gives compile time error.

Some thing like ambiguous.

[Matthew Brown]

That's right. Because Integer and String are in different parts of the inheritance tree - neither is a parent of the other - the compiler doesn't consider one to be more specific than the other. So it doesn't know which version to call, and so you get the error.

But Object is a parent of String, so the String version is more specific than the Object version.

You can get round the ambiguity, if necessary, by using an explicit cast:
method1((Integer)null);