Inheritance in java

IMPLEMENTATION OF
INHERITANCE
IN JAVA AND C#

INHERITANCE..

 As the name suggests, inheritance means to take something that is
already made.
 It is one of the most important feature of Object Oriented
Programming.
 It is the concept that is used for reusability purpose.
 Inheritance is the mechanism through which we can derived
classes from other classes.
 The derived class is called as child class or the subclass or we can
say the extended class and the class from which we are deriving the
subclass is called the base class or the parent class.

TYPES OF INHERITANCE
The following kinds of inheritance are there in java.
 Simple Inheritance
 Multilevel Inheritance
 Hierarchical inheritance
 Use case of Interfaces (Multiple,Hybrid Inheritance)

INHERITANCE
Simple Inheritance
When a subclass is derived simply from it's parent class
then this mechanism is known as simple inheritance.
Multilevel Inheritance
 The process of a subclass is derived from a derived class.

 In multilevel, one-to-one ladder increases.

 Multiple classes are involved in inheritance, but one class
extends only one.
 The lowermost subclass can make use of all its super classes'
members.

INHERITANCE
Hierarchical Inheritance
 In hierarchical type of inheritance, one class is extended by many
subclasses.
 It is one-to-many relationship.

Multiple Inheritance
 The process of more than one subclass is derived from a same
base class.
 In multiple, many-to-one ladder increases.

 Multiple classes are involved in inheritance, but one class extends
only one.

INHERITANCE

 Hybrid Inheritance
Hybrid Inheritance is the combination of
multiple, hierarchical inheritance.

IMPLEMENTATION OF INHERITANCE IN
JAVA

INHERITANCE IN JAVA
To know about the concept of inheritance in java we should know
about the following concepts,
methods,

 data members,

 access controls,

 constructors,

 Key words

‘ this ’,
‘ super ‘etc.
To derive a class in java the keyword extends is used.

‘SUPER’ KEYWORD
.
As the name suggest super is used to access the members of the
super class.
It is used for two purposes in java.
1. The first use of keyword super is to access the hidden data
variables of the super class hidden by the sub class.
e.g. Suppose class A is the super class that has two instance
variables as int a and float b.
class B is the subclass that also contains its own data
members named a and b.
Then we can access the super class (class A) variables a and
b inside the subclass class B just by calling the following
command.
super.member;

CONT..
2.Use of super to call super class constructor: The second
use of the keyword super in java is to call super class
constructor in the subclass.
This functionality can be achieved just by using the
following command.
super(param-list);
 Here parameter list is the list of the parameter requires by the
constructor in the super class.
 super must be the first statement executed inside a super class
constructor.
 If we want to call the default constructor then we pass the
empty parameter list.

‘THIS’ KEYWORD
 The keyword ’this’ is useful when we need to refer to instance of
the class from its method.
 ‘this’ keyword helps us to avoid name conflicts.
 As we can see in the program that we have declare the name of
instance variable and local variables same.
 The keyword this will reference the current class the word appears
in.
 It will allow you to use the classes methods if used like this
this.methodName();

ACCESS SPECIFIERS IN JAVA
There are four Access Specifiers in Java
1. Public: When a member of a class is declared as public
specifier, it can be accessed from any code.

2. Protected: Protected is only applicable in case of
Inheritance. When a member of a class is declared as
protected, it can only be accessed by the members of its class
or subclass.

3. Private: A member of a class is declared as private
specifier, can only be accessed by the member of its class.

4. Default: When you don't specify a access specifier to a
member, Java automatically specifies a default. And the
members modified by default can only be accessed by any
other code in the package, but can't be accessed outside of a
package.

AN EXAMPLE OF MULTI LEVEL INHERITANCE

 A Scenario where one class is inheriting/extending the behaviour
of another class which in turn is inheriting behavior from yet
another class.

Ex: public class Automobile {…}
Public class Car extends Automobile {…}
Public class Ferrari extends Car {…}

This multilevel inheritance actually has no limitations on the
number of levels it can go.
 So as far as java goes, it is limitless. But for maintenance and ease
of use sakes it is better to keep the inheritance levels to a single
digit number.

EXAMPLE:

class Aves
{ Aves
public void nature() {
System.out.println(”Aves fly"); }
} Bird
class Bird extends Aves
{
Parrot
public void eat(){
System.out.println("Eats to live"); }
}
class Parrot extends Bird
{
public void food() {
System.out.println("Parrot eats seeds andfruits"); }

CONT..

public static void main(String args[])
{
Parrot p1 = new Parrot();
p1.food(); // calling its own
p1.eat(); // calling super class Bird
method
p1.nature(); // calling super class Aves
method
}
}

HOW TO DO MULTIPLE INHERITANCE IN JAVA?

Actually, java does not support multiple inheritance

However, you can achieve partial multiple inheritance with the
help of interfaces.

Ex: public class FerrariF12011 extends Ferrari implements Car,
Automobile {…}

And this is under the assumption that Car and Automobile are
interfaces.

INTERFACES IN JAVA
 An interface is a container of abstract methods.
 It allows Java to implement Multiple Inheritance, because a class
can't have more than one superclass in Java, but can implements
many interfaces.
 Methods are just declared in interface, but not defined. The class
which implements an interface must have to define the method
declared in the interface.
 Access modifiers and return type must be same as declared in the
interface.
 Private and static methods can't be declared in the interface.

WHY DOESN'T JAVA ALLOW MULTIPLE
INHERITANCE?
Let us say the Automobile Class has a drive() method and the Car
class has a drive() method and the Ferrari class has a drive()
method too.
Let us say we create a new class FerrariF12011 that looks like
below:
Public class FerrariF12011 extends Ferrari, Car, Automobile {…}

And at some point of time we need to call the drive() method, what
would happen?
Our JVM wouldn't know which method to invoke and we may have
to instantiate one of the classes that you already inherit in order to
call its appropriate method.
To avoid this why the creators of java did not include this direct
multiple inheritance feature.

EXAMPLE
interface Suzuki
{ Suzuki Ford
public abstract void body();
}
interface Ford
{ MotorCar
public abstract void engine();
}
public class MotorCar implements Suzuki, Ford
{
public void body()
{
System.out.println("Fit Suzuki body");
}

CONT..

public void engine()
{
System.out.println("Fit Ford engine");
}
public static void main(String args[]) {
MotorCar mc1 = new MotorCar();
mc1.body();
mc1.engine();
}}

How it works???
In the above code there are two interfaces – Suzuki and
Ford.
Both are implemented by MotorCar because it would like to
have the features of both interfaces
 Just to inform there are multiple interfaces and not classes,
tell the compiler by replacing "extends" with "implements”.
 MotorCar, after implementing both the interfaces, overrides
the abstract methods of the both – body() and engine(); else
program does not compile.

‘FINAL’ KEYWORD
 It can also be called as Restricting Inheritance
 Classes that cant be extended are called final classes.
 We use the final modifier in the definition of the class to
indicate this.
final class myclass
{
// Insert code here
}

IMPLEMENTATION OF INHERITANCE IN C#

INHERITANCE IN C#
 Syntax for deriving a class from a base class
class Token
{ Derived class Base class
...
}
class CommentToken: Token
{
... Colon
}
 A derived class inherits most elements of its
base class
 A derived class cannot be more accessible
than its base class

CALLING BASE CLASS CONSTRUCTORS
 Constructor declarations must use the base keyword
class Token
{
protected Token(string name) { ... }
...
}
{
public CommentToken(string name) : base(name) { }
 A private base class constructor cannot be accessed by a
...derived class
}  Use the base keyword to qualify identifier scope

DEFINING VIRTUAL METHODS
 Syntax: Declare as virtual
class Token
{
...
public int LineNumber( )
{ ...
}
public virtual string Name( )
{ ...
}
}  Virtual methods are polymorphic

OVERRIDING METHODS

 Syntax: Use the override keyword

class Token
{ ...
public virtual string Name( ) { ... }
}
{ ...
public override string Name( ) { ... }
}

WORKING WITH OVERRIDE METHODS
You can only override identical inherited virtual methods
class Token
{ ...
public int LineNumber( ) { ... }
}


{ ...
public override int LineNumber( ) { ... }

}

 You must match an override method with its associated virtual
method
 You can override an override method
 You cannot explicitly declare an override method as virtual
 You cannot declare an override method as static or private

USING NEW TO HIDE METHODS

 Syntax: Use the new keyword to hide a
method
class Token
{ ...
}
{ ...
new public int LineNumber( ) { ... }

}

WORKING WITH THE NEW KEYWORD
 Hide both virtual and non-virtual methods
class Token
{ ...
}
{ ...
new public int LineNumber( ) { ... }
}

 Resolve name clashes in code
 Hide methods that have identical signatures

MULTI LEVEL INHERITANCE

 Multi Level Inheritance is supported in C#.
 Any level of inheritance is possible to inherit
a class “:” is used after the class name.
 Like „super‟ keyword in Java, here we have
„base‟ keyword which can be used during
header initialization.
 It will invoke the immediate base class of the
calling class.

SAMPLE PROGRAM
class person
{
string name; Person
int age;
public person()
{
Console.Write("Enter Name : "); Employee
name = Console.ReadLine();
Console.Write("Enter age : ");
age = Convert.ToInt32(Console.Read()); Program
}
public virtual void put_data()
{
Console.Write("Name : " + name);
Console.Write("Age : " + age);
}
}

CONT..
class employee : person
{
int salary;
public employee()
{
Console.Write("Enter Salary : ");
salary = Convert.ToInt32(Console.Read);
}
public override void put_data()
{
Console.Write("Salary : " + salary);
}
}

CONT..
class Program : employee
{
static void Main(string[] args)
{
employee e1 = new employee();
e1.put_data();
Console.WriteLine("Press any key to exit...");
Console.ReadLine();

}
}

MULTIPLE INHERITANCE

 Like Java C# does‟nt have multiple
inheritance.
 The reason is same that of java.

 We can perform that through interfaces we
can implement any number of interfaces.

DECLARING INTERFACES

Interface names should
begin with a capital “I”

interface IToken
IToken
{
« interface »
int LineNumber( );
string Name( ); LineNumber( )
} Name( )

No access specifiers No method bodies

IMPLEMENTING MULTIPLE INTERFACES
 A class can implement zero or more interfaces

interface IToken
{
string Name( ); IToken IVisitable
} « interface » « interface »
interface IVisitable
{
void Accept(IVisitor v);
}
class Token: IToken, IVisitable
{ ... Token
}

 An interface can extend zero or more interfaces
 A class can be more accessible than its base interfaces
 An interface cannot be more accessible than its base
interfaces
 A class must implement all inherited interface methods

IMPLEMENTING INTERFACE METHODS
 The implementing method must be the same as the
interface method
 The implementing method can be virtual or non-
virtual
Same access
class Token: IToken, IVisitable Same return type
{ Same name
public virtual string Name( ) Same parameters
{ ...
}
public void Accept(IVisitor v)
{ ...
}
}

Inheritance in java

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Inheritance in java