Java Inheritance Easy Lesson
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Wednesday, October 29, 2008

Java Inheritance Easy Lesson

Inheritance involves creating new classes from the existing ones. it provides the ability to take the data and methods from an existing class and derive a new class. The keyword extends is used to inherit data and methods from a existing class. the extends keyword is used as

class New_Class extends Old_Class { ....... }

The inherited methods and data are those that are declared public or protected inside the super class. Using(Extending) same Engine.

Note: private members are not inherited. Here key is private

Java Access Modifiers Lesson

Eg How Inheritance works.

class Add

int x;
int y;

public int Add_xy()

int sum=0;
return sum;


class Sub extends Add
public int Sub_xy()
int sub;
return sub;

class Inheritance
pubic static void main(String args[])
Sub sub_obj=new Sub();
int a=sub_obj.Add_xy();
int s=sub_obj.Sub_xy();
System.out.println("x value is "+sub_obj.x);
System.out.println("y value is "+sub_obj.y);
System.out.println("sum is "+a);
System.out.println("subtraction is "+s);

Download Source

>java Inheritance


x value is 10;
y value is 4;
sum is 14;
subtraction is 6;

Note : The object of the sub-class was created inside the main. The class Sub extends the class Add. This ist derives all the protected and public members of the class Add. The class Sub contains a method of it own, Sub_xy()/ The Object of class Sub in the main() is used to assign values to x and y and then the two methods are called.

Java does not support multiple inheritance directly. This means that the class in Java cannot have more than one super class.


class Derived extends Super_one, Super_two

is illegal/not permitted in Java.

However, to be able to let the java programmers use the immense functionality provided by multiple inheritance, the java language developers incorporated this concept with the use of interfaces. (I will post an article about Interfaces with in few days)
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  1. A wrong example for inheritance

    An important aspect which is missing, is the relationship between the super-class and the derived sub-class.
    Inheritance should be used when we see an "is a" relationship.
    The example of Sub extends Add would be incorrect since
    we can't say that Sub is a Add.
    Always when using inheritance check whether you have the "is a" relationship.
    Do not inherit for the sake of inheriting methods from another class.
    The two classes should have a natural "is a" relation.

  2. Very interesting.. this is Great Coding Technique.. Very interesting.. Post Awesome post.. Thanks


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