null is what type of data type

[Mohan Vinukonda]

method passing null to the called function, compiler would take that parmer as what type of paramer???

[Peter Chase]

If there is only one overload of the named method that matches the other parameters (the ones that aren't null at compile time), then that one is chosen. If there is more than one, you get a compiler error.

You can tell the compiler which one you want, by casting your null to an appropriate type. For example: -

void foo(Bar b) { ... }
 
void foo(Baz z) { ... }
 
void doStuff()
{
  foo((Bar) null); // legal - calls foo(Bar)
  foo(null); // compiler error
}

[Mohan Vinukonda]

static void method(Object obj){
System.out.println("Object");
}
static void method(String str){
System.out.println("String");
}

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


for this I am not getting compilation error with out type cast

[Chris Corbyn]

I imagine that's because "Object" will always be satisfied anyway...

[Henry Wong]

Originally posted by MohanRao Vinukonda:
static void method(Object obj){
System.out.println("Object");
}
static void method(String str){
System.out.println("String");
}

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


for this I am not getting compilation error with out type cast

If there are two cases to choose from, the compiler will first try to pick the more specific case. In this case, String will be picked over Object.

Otherwise, Peter is correct. You will have to cast to help the compiler, or it will complain.

Henry

[marc weber]

Also see this item from our SCJP FAQ: What is a most-specific method?
[ September 04, 2007: Message edited by: marc weber ]

[Mohan Vinukonda]

I have understood the concept now... Thnx all of you.

What could be the data type of null ???

[marc weber]

Originally posted by MohanRao Vinukonda:
...What could be the data type of null ???

Actually, null is a special type. According to JLS - 3.10.7 The Null Literal...

The null type has one value, the null reference, represented by the literal null... A null literal is always of the null type.

A null reference can be upcast to any type of Object.

[mvan le]

Mohan Vinukonda wrote:method passing null to the called function, compiler would take that parmer as what type of paramer???

Since Java 1.6, the "javax.lang.model.type.NullType" interface represents the null type. Ie. This is the type of the expression ``null''.

Example:

package Test;

import javax.lang.model.type.NullType;

public class NullConstructor
{
    public NullConstructor()
    {
        super();
        System.out.println("No argument constructor");
    }
    
    public NullConstructor(Object o)
    {
        super();
        System.out.println("Object constructor");
    }

    public NullConstructor(NullType o)
    {
        super();
        System.out.println("NullType constructor");
    }    

    public static void main(String[] args)
    {
        NullConstructor nullConstructor1 = new NullConstructor();
        NullConstructor nullConstructor2 = new NullConstructor((NullType) null);
        NullConstructor nullConstructor3 = new NullConstructor((Object) null);
        NullConstructor nullConstructor4 = new NullConstructor(null);
    }
}

Would produce the following output:

    No argument constructor
    NullType constructor
    Object constructor
    NullType constructor

Notice that the nullConstructor4 instance created from "new NullConstructor(null);" (where null is not explicitly cast) selects the constructor with parameter type NullType rather than Object.

[Campbell Ritchie]

And welcome to the Ranch mvan le