y null????

[muskaan gaffor]

hi,
can anyone tell me why the following code's output is "null" instead of "Person"?

class Person{
private String sName="Person";
public String getName(){
return sName;
}
public void setName(String sName){
this.sName=sName;
}
}
class User extends Person{
private String sName;
public String getName(){
return sName;
}
public void setName(String sName){
this.sName=sName;
}

}

public class Killer{
private String sName;
public static void main(String argv[]){
new Killer();
}
Killer(){
Person p = new User();
System.out.println(p.getName());

}
}

thanks in advance!!!
regards
pbg!!!

[Christophe Verré]

Because p is a User instance, whose name is never set
(both User and Person have private String sName)

[muskaan gaffor]

Originally posted by Satou kurinosuke:
Because p is a User instance, whose name is never set
(both User and Person have private String sName)

thanks Satou....how it works even sname is declared as private in all the classes?

[Kishore Balla]

Originally posted by pb gaffor:


thanks Satou....how it works even sname is declared as private in all the classes?

p is reference variable of Person type but its object is of User type..

So, at compile it will look for getName in Person class. But at Runtime, the getName() in User Class will get executed and since sName is User class is not initialized the default (null) will get printed

[Sreeram Desigan]

The variable p in killer class constructor is a base class reference and it is made to refer derived class (User). when the base class reference refers to a derived class and a method is invoked using the reference then the derived class method is called. Hence the getName() method in User class is called. The method returns SName which is the User class variable. This variable is not yet initialized in the User class. Hence it has null value which is default initiaization for strings. The SName of user is different from the SName for Person. Initializing for Person is not sufficient for User.

[muskaan gaffor]

thank u