3. Inheritance in Java
Inheritance is an important pillar of OOP
(Object Oriented Programming). It is the
mechanism in java by which one class is
allow to inherit the features (fields and
methods) of another class.
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4. 4
Important Terminology
• Super Class: The class whose features are inherited is known as super
class(or a base class or a parent class).
• Sub Class: The class that inherits the other class is known as sub
class(or a derived class, extended class, or child class). The subclass
can add its own fields and methods in addition to the superclass fields
and methods.
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Important Terminology (cont.)
• Reusability: Inheritance supports the concept of “reusability”, i.e. when
we want to create a new class and there is already a class that
includes some of the code that we want, we can derive our new class
from the existing class. By doing this, we are reusing the fields and
methods of the existing class.
6. How to Use Inheritance in Java?
The keyword used for inheritance is extends. Syntax:
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class derived-class extends base-class
{
//methods and fields
}
8. Illustration Explanation
In previous illustration, when an object of MountainBike class is
created, a copy of the all methods and fields of the superclass acquire
memory in this object. That is why, by using the object of the subclass
we can also access the members of a superclass.
Please note that during inheritance only object of subclass is created,
not the superclass. For more, refer Java Object Creation of Inherited
Class.
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Types of Inheritance
There are Various types of inheritance:
• Single Inheritance
• Multiple Inheritance
• Multilevel Inheritance
• Hierarchical Inheritance
• Hybrid Inheritance
Note: Java doesn't support hybrid/Multiple inheritance
10. Single Inheritance
In Single Inheritance one class extends another class (one class only).
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In above diagram, Class B extends only Class A. Class A is a super class
and Class B is a Sub-class.
11. Multiple Inheritance
In Multiple Inheritance, one class extending more than one class. Java
does not support multiple inheritance.
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As per above diagram, Class C extends Class A and Class B both.
12. Multilevel Inheritance
In Multilevel Inheritance, one class can inherit from
a derived class. Hence, the derived class becomes
the base class for the new class.
As per shown in diagram Class C is subclass of B
and B is a of subclass Class A.
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14. Hybrid Inheritance
Hybrid inheritance is a combination of Single and Multiple inheritance.
Java doesn't support hybrid inheritance
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As per above example, all the public and protected members of Class A are
inherited into Class D, first via Class B and secondly via Class C.
15. Important Facts of Inheritance in Java
• Default superclass: Except Object class, which has no superclass, every
class has one and only one direct superclass (single inheritance). In the
absence of any other explicit superclass, every class is implicitly a
subclass of Object class.
• Superclass can only be one: A superclass can have any number of
subclasses. But a subclass can have only one superclass. This is
because Java does not support multiple inheritance with classes.
Although with interfaces, multiple inheritance is supported by java.
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16. Important Facts of Inheritance in Java (cont.)
• Inheriting Constructors: A subclass inherits all the members (fields,
methods, and nested classes) from its superclass. Constructors are not
members, so they are not inherited by subclasses, but the constructor
of the superclass can be invoked from the subclass.
• Private member inheritance: A subclass does not inherit the private
members of its parent class. However, if the superclass has public or
protected methods(like getters and setters) for accessing its private
fields, these can also be used by the subclass.
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17. So, Why and When to Use "Inheritance"?
The most important use is the reusability of code. The code that is
present in the parent class doesn’t need to be written again in the child
class.
What is the meaning? With inheritance, we can reuse attributes and
methods of an existing class when you create a new class.
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18. Thank You, Next …
Polymorphism
Study Program of Informatics
Faculty of Engineering and Computer Science
SY. 2019-2020
Andi Nurkholis, S.Kom., M.Kom.
April 16, 2020
