Why the interviewer challenged me?

[Maki Jav]

Recently i was interview for a job. The interviewer asked me whether static methods get inherited? I said yes they do! He said, "really? try it"

What was I missing?
For example:

Parent class

public class ParentClass{
 
 public static void staticMethod(){
     System.out.println("staticMethod() called");
 

 }
 

 public void nonStaticMethod(){
     System.out.println("nonStaticMethod() called");
 
 }
 
}

Child class

public class ChildClass extends ParentClass{
 
  public void supercall(){
     nonStaticMethod();
  }
 
 public static void main(String args[]){
staticMethod();
new ChildClass().supercall(); 
       
 }
 
}

compiles easily and that static and non-static methods are called without any problem.

Any comments?

Maki Jav

[greg buela]

I think what he meant is that they don't work polymorphically*, as instance methods do. In that case, I think you answered correctly and he made a poor, or ambiguous, choice of words.

(*) As in overriding the static method, having a supertype reference pointing to a subtype object, and making the subtype method execute invoked with the supertype reference.

[Maki Jav]

Oh you mean...

abstract class HumanBeing{
 
 void printName();
 static int getQuantity(){ return 1;} // every human being is an individual
 
}
 
 
 class Albert extends HumanBeing{
 
    void printName(){ System.out.println("I am Albert");}
    static int getQuantity(){ return 2;}// there are two "Alberts" here
 
}
 
 
 public TestClass{
 
  public static void main(String args[]){
  
     HumanBeing human = new Albert();
 
    human.printName(); // prints
    human.getQuantity(); // does not work!
   
  }
 
 
}

I have not tested it but will it work? Comments?

Thank you,

Maki Jav
[ September 25, 2007: Message edited by: Maki Jav ]

[Brian Cole]

Originally posted by Maki Jav:
Recently i was interview for a job. The interviewer asked me whether static methods get inherited? I said yes they do! He said, "really? try it"

What was I missing?

The term "inherited" is somewhat ambiguous. The child class can of course call the parent's static method (without the "ParentClass." prefex), so it is inherited in that sense.

What the interviewer was trying to ask is if static methods can be overridden. (They can't.) Simple example:

public class StaticOverride {
 
static class ParentClass {

public static void staticMethod() {
System.out.println("static in parent");
}
public void nonStaticMethod() {
System.out.println("non-static in parent");
}
}

static class ChildClass extends ParentClass {

public static void staticMethod() {
System.out.println("static in child");
}
public void nonStaticMethod() {
System.out.println("non-static in child");
}
}

public static void main(String[] argv) {

ParentClass foo = new ChildClass();

foo.nonStaticMethod(); // prints "non-static in child"
foo.staticMethod(); // prints "static in parent"
}

}

In this case ChildClass has its own staticMethod() which shadows (but doesn't override) the method of same name in ParentClass. (I prefer the term shadow but some use the term hide.)

The point is that while it is legal to write "foo.staticMethod()" it doesn't really make sense to do so. It's better to write either "ParentClass.staticMethod()" or "ChildClass.staticMethod()" since that's how the compiler handles it anyway.

[edit: I see your Albert/Human example is similar. It's not that human.getQuantity() "does not work", just that it is a call to the static method in the Human class, not in the Albert class. Since getQuantity() is static, it's the declared type of human that matters, not the actual type that is referenced at runtime.]
[ September 25, 2007: Message edited by: Brian Cole ]