Mock question

[Anonymous]

Hi!
Can someone explain me a behaviour of this program and what will be the output?
Q13.What will be the result of compiling and running the given program?
Select one correct answer.
1 class sample
2 {
3 sample(String s)
4 {
5 System.out.println("String");
6 }
7 sample(Object o)
8 {
9 System.out.println("Object");
10 }
11 }
12 class constructor
13 {
14 public static void main(String arg[])
15 {
16 sample s1=new sample(null);
17 }
18 }
thank you in advance.

[Anonymous]

The output will be "String" as null is not an object.

[Anonymous]

Hi Shyamsundar, I don�t understand because null is not a String.

Sample s1 = null; ------> compile
String s = null; ------> compile

[Jose Botella]

In the JLS 15.2 section method invocations are dealt with
Sample(String) is chosen because is more specific than Sample(Object)
It is more specific because String can be coneverted via a wideninnig convertion (or identity conversion) to object.
Sample(Object) is not more specific than Sample(String) because Object can't be converted via widenning conversion (or identity) to String
So null is not the reason here.

[Anonymous]

Thanks Jose...
I understand it now... When I comment out the
method having a string as an argument, the program prints "Object".
But regarding "null", a question still remains in my mind. I wrote a small program..

class test{
     test(String o){
     System.out.println("A null object has been created");
     System.out.println(o.length());
     }   
}
public class test1{
     public static void main(String[] args){
     test a = new test(null);
     }
}

This program gave the following output...

A null object has been created
Exception in thread "main" java.lang.NullPointerException
        at test.<init>(test1.java:4)
        at test1.main(test1.java:10)

This means that while a null object can be created, no operaton can be carried out on it..right?... While I can understand the exception at line 4, I fail to do so for line 10.
Do comment on this.
Thanks in Advance
Shyam
[This message has been edited by Shyamsundar Gururaj (edited September 09, 2001).]