 Inheritance introduction
 is – a relationship & has – a relationship
 Super classes and Sub classes
 Types of inheritance
 Single inheritance
 Hierarchical inheritance
 Multilevel inheritance
 Multiple inheritance

 A form of software reuse in which a new class is created by absorbing an existing class’s members and adding them with new or modified capabilities.
 Can save time during program development by basing new classes on existing proven and debugged high-quality software.
 Increases the likelihood that a system will be implemented and maintained effectively.

 When creating a class, rather than declaring completely new members, you can designate that the new class should inherit the members of an existing class.
 Existing class is the superclass
 New class is the subclass
 Each subclass can be a superclass of future subclasses.
 A subclass can add its own fields and methods.
 A subclass is more specific than its superclass and represents a more specialized group of objects.
 The subclass exhibits the behaviors of its superclass and can add behaviors that are specific to the subclass.

 The private members of the superclass are private to the superclass.
 The subclass can directly access the public members of the superclass.
 The subclass can include additional data and method members.
 All data members of the superclass are also data members of the subclass. Similarly, the methods of the superclass (unless overridden) are also the methods of the subclass.

The is a relationship is expressed with inheritance and has a relationship is expressed with composition.
For Example: For Example:
} is a --- House is a Building class Building {
.......
class House extends Building {
}
.........
has a -- House has a bathroom
{ class House
Bathroom room = new Bathroom() ;
....
}
{ public void getTotMirrors() room.getNoMirrors();
}
....

Inheritance Vs Composition
Inheritance is uni-directional. For example House is a Building. But Building is not a House. Inheritance uses extends key word.
Composition: is used when House has a Bathroom. It is incorrect to say House is a Bathroom.
Composition simply means using instance variables that refer to other objects.
The class House will have an instance variable, which refers to a Bathroom object.

 Classes can be derived from other classes. The derived class (the class that is derived from another class) is called a
. The class from which its derived is called the
.

 In fact, in Java, all classes must be derived from some class. Which leads to the question
The top-most class, the class from which all other classes are derived, is the Object class defined in java.lang. Object is the root of a hierarchy of classes.

 Example

 Figure shows a sample university community class hierarchy. Also called an inheritance hierarchy.
 Each arrow in the hierarchy represents an is-a relationship.
 Follow the arrows upward in the class hierarchy
 An Employee is a CommunityMember ”
 “a Teacher is a Faculty member.”
 CommunityMember is the direct superclass of Employee, Student and Alumnus and is an indirect superclass of all the other classes in the diagram.
 Starting from the bottom, you can follow the arrows and apply the
up to the topmost superclass.

Four kinds of inheritance in JAVA. They are.
 Single Inheritance (Only one super class).
 Multilevel Inheritance (Derived from a derived class).
 Hierarichal Inheritance (one Super class, many subclasses).
 Multiple Inheritance (Several Super classes).

Pictorial Representation:

 When a subclass is derived simply from it's parent class then this mechanism is known as single inheritance. In case of single inheritance there is only a sub class and it's parent class. It is also called one level inheritance.
 For Example package yuc.edu.sa; public class SingleInhertiance
{ int x; int y; public void set(int p, int q){ x=p; y=q;
}
}
} void Show(){
System.out.println(x); package yuc.edu.sa; public class SingleInhertianceApp extends
SingleInhertiance { public static void main(String[ ] args) {
SingleInhertiance singleInhertiance = new SingleInhertiance(); singleInhertiance.set(10, 20); singleInhertiance.Show();
}
}

 One Parent class has many sub classes. And this is the concept of Hierarchical
Inheritance.
 For Example:

Output:

 Derived from a derived class. Such concept is called Multilevel inheritance.
 For Example:

Output:


The mechanism of inheriting the features of more than one base class into a single class is known as
. Java does not support multiple inheritance but the multiple inheritance can be achieved by using the
.