Static members | Inheritance

[Puja Sinha]

Hi,

I ran the following code :

public class TestStatic {
	public static void main (String[] args) {
		Child.printClass();
		System.out.println(Child.CLASS);
	}
}

class Parent {
	
	public static String CLASS = "parent";
	
	public String animal = "ZEBRA";
	
	public static void printClass() {
		System.out.println(" This is the parent class");
	}
	
	public void printOriginal() {
		System.out.println(" this is the original method");
	}
}

class Child extends Parent {
	
	//public static String CLASS = "child";
	
	/*public static void printClass() {
		System.out.println(" This is the child class");
	}*/
	
	public void printOriginal() {
		System.out.println(" this is the duplicate method");
	}
}

It printed :

This is the parent class
parent

Why does this happen , when we say that the static members are not inherited.

Thanks in advance.
Puja

[Matthew Brown]

Puja Sinha wrote:Why does this happen , when we say that the static members are not inherited.

We don't say that (well, maybe some people do ) - we say they are not overridden.

[Ikpefua Jacob-Obinyan]

Matthew Brown wrote:
We don't say that (well, maybe some people do ) - we say they are not overridden.

Hello Guys...@Matthew I am tempted to believe that a lot of people 'say-and-think' that static members are NOT inherited, I have encountered that in this forum and other forums. One other thing I want to say is that static methods CANNOT be polymorphically overridden rather 'redifined'.

Regards

Ikpefua.

[Tommy Delson]

Matthew Brown wrote:

Puja Sinha wrote:Why does this happen , when we say that the static members are not inherited.

We don't say that (well, maybe some people do ) - we say they are not overridden.

I think your guys mixed up with Polymorphism, Inheritance, and Overridden Static Members. Below is a modified version that may help....

public class TestStatic {
	public static void main (String[] args) {

		Child.printClass(); //Calling printClass() method in Parent class since Child extends Parent
							//and inherited all non-static or static public and protected members of Parent.

		System.out.println(Child.CLASS); /*Calling static member or variable "CLASS" in Parent class since Child extends Parent
							               and inherited all non-static or static  public and protected members of Parent.

							            This has nothing to do with "static members are not inherited.".



							            */
		//Polymorphism in action...
		Parent pa = new Child(); //How do you interpret this line?
		pa.printClass(); //What is the output if PrintClass() method in Child is uncommented ??
						 //Output: This is the parent class (Calling printClass() method in Parent so, static method is not selected here. In other word,
                                                 //only instance method is called at runtime on an actual object Child.

		System.out.println(pa.CLASS); //What is the output and why?
									  
		
		//Child class in action
		Child c = new Child();
		c.printClass(); //What is the output if PrintClass() method in Child is uncommented ??

		System.out.println(c.CLASS); //What is the output?





	}
}

class Parent {

	public static String CLASS = "parent";

	public String animal = "ZEBRA";

	public static void printClass() {
		System.out.println(" This is the parent class");
	}

	public void printOriginal() {
		System.out.println(" this is the original method");
	}
}

class Child extends Parent {


	public static String CLASS = "child"; //If this uncomment, it will SHADOWING static class variable "CLASS
											//in Parent class.

	public static void printClass() { //This method belongs to Child class SHADOWING printClass() method in Parent class.
		System.out.println(" This is the child class");
	}

	public void printOriginal() {
		System.out.println(" this is the duplicate method");
	}
}


/*



Recap from K & B book: Chapter 2, page 140 on Object Orientation

Polymorphic method invocations apply only to instance methods. You can
always refer to an object with a more general reference variable type (a superclass
or interface), but at runtime, the ONLY things that are dynamically
selected based on the actual object (rather than the reference type) are instance
methods. Not static methods. Not variables. Only overridden instance methods
are dynamically invoked based on the real object's type.


*/

[Tommy Delson]

Ikpefua Jacob-Obinyan wrote:

Matthew Brown wrote:
We don't say that (well, maybe some people do ) - we say they are not overridden.

Hello Guys...@Matthew I am tempted to believe that a lot of people 'say-and-think' that static members are NOT inherited, I have encountered that in this forum and other forums. One other thing I want to say is that static methods CANNOT be polymorphically overridden rather 'redifined'.

Regards

Ikpefua.

Here is what Ikpefua Jacob meant:

Recap from K & B book: Chapter 2, Page 151

Finally, remember that static methods can't be overridden! This doesn't mean they
can't be redefined in a subclass, but redefining and overriding aren't the same thing.
Let's take a look at an example of a redefined (remember, not overridden), static
method:

class Animal {
static void doStuff() {
System.out.print("a ");
}
}
class Dog extends Animal {
       static void doStuff() { // it's a redefinition, not an override
                System.out.print("d ");
       }
        public static void main(String [] args) {
                Animal [] a = {new Animal(), new Dog(), new Animal()};
                for(int x = 0; x < a.length; x++)
                     a[x].doStuff(); // invoke the static method
         }
}

Running this code produces the output:
a a a

[Seetharaman Venkatasamy]

http://www.coderanch.com/t/368681/java/java/statics-inherited

[Ikpefua Jacob-Obinyan]

Tommy Delson wrote:I think your guys mixed up with Polymorphism, Inheritance, and Overridden Static Members.

Hello Tommy, your 'modus-operandi' of using codes to dialogue in this forum is from my point of view the most effective way to clarify doubts in Java. In addition I want to mention that if you carefully read Matthew and Puja's posts you will notice that there was NO "mix-up", Puja placed his arguments or doubts and Matthew replied with a simple and straight forward answer that you and I followed up. So who's mixing up what?

Regards

Ikpefua

[Tommy Delson]

Ikpefua Jacob-Obinyan wrote:

Tommy Delson wrote:I think your guys mixed up with Polymorphism, Inheritance, and Overridden Static Members.

Hello Tommy, your 'modus-operandi' of using codes to dialogue in this forum is from my point of view the most effective way to clarify doubts in Java. In addition I want to mention that if you carefully read Matthew and Puja's posts you will notice that there was NO "mix-up", Puja placed his arguments or doubts and Matthew replied with a simple and straight forward answer that you and I followed up. So who's mixing up what?

Regards

Ikpefua

Yup, that's TRUE using codes to clarify doubt in Java is the best approach to understand and learn how Java works. The Compiler is an ultimate Tool to clarify our doubts so, utilize it as much as we could.


Sound like you're ready for the Final SCJP Exam....go for it if you're ready!

[Ikpefua Jacob-Obinyan]

Tommy Delson wrote:Sound like you're ready for the Final SCJP Exam....go for it if you're ready!

Everybody tells me that... ...Thanks for the beerchug and motivation! I sincerely think I am ready, funny enough most people think I have it already... I will give it a try in a few weeks from now, lets see how it goes...Wish me luck...

Regards

Ikpefua.

[Tommy Delson]

Ikpefua Jacob-Obinyan wrote:

Tommy Delson wrote:Sound like you're ready for the Final SCJP Exam....go for it if you're ready!

Everybody tells me that... ...Thanks for the beerchug and motivation! I sincerely think I am ready, funny enough most people think I have it already... I will give it a try in a few weeks from now, lets see how it goes...Wish me luck...

Regards

Ikpefua.

Good luck and let us know how it goes...