Inheritance

[M Rama]

package inheritance;
 
public class A extends B {
 
String str = "Child";
 
static void print() {
System.out.println("Child Class");
}
 
public static void main(String[] args) {
A a = new A();
a.exec();
 
B b = new A();
b.exec();
 
}
}
 
class B {
 
String str = "Parent";
 
static void print() {
 
System.out.println("Parent Class");
}
 
void exec() {
print();
 
System.out.println(str);
}
 
}

Prints:

Parent Class
Parent
Parent Class
Parent

whereas:

 
package inheritance;
 

public class A extends B {
 
String str = "Child";
 
static void print() {
System.out.println("Child Class");
}
void exec() {
print();
 
System.out.println(str);
}
 
public static void main(String[] args) {
A a = new A();
a.exec();
 
B b = new A();
b.exec();
 
}
}
 
class B {
 
String str = "Parent";
 
static void print() {
 
System.out.println("Parent Class");
}
 
void exec() {
print();
 
System.out.println(str);
}
 
}

Prints:
Child Class
Child
Child Class
Child


I understand the static method printing. But not the instance variable str.

Is this material covered in K&B( Chapter 5 doesn't have it and I am yet to read 3 and 6 from first 9 )? Is there a different book I need to read for this?

[Raghu Shree]

Hi,
Static methods are cannot be overriden. So it is execute current class methods like print(). Once again I noticed, Instance members are cannot be overriden. It is hiding. In Overriding Methods are executed based on the Object reference. But memebers variables ae accessed based on class. ie., classname.variable. If u have any more doubts walk through the code available in your previous posting
https://coderanch.com/t/248659/java-programmer-SCJP/certification/abstract-class-protected-member-behaviour.

[Sakthi Kani]

hai rama,
as far as ur program is concerned,u r trying to access a static method.
in general,static methods take the reference and not objects & so u get the result (as mentioned in ur 1st code).


----------------------------------------------------------------------------

I understand the static method printing. But not the instance variable str.

----------------------------------------------------------

instance variables are similar in behaviour to static methods,they too refer only the reference and not the objects.
hence according to ur code(both 1st & 2nd ),u r creating the reference for the class & trying to print the str(instance variable)from that class,since instance variables refer to references & not objects,it takes the value os str in that particular class which it refers to.

if still not clear,plz reply

regards
-sakthi