sub classes

8/2/2019 Sub Classes

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Sub Classes


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Sub Classes

The process of creating a new class from theexisting class is called as Sub Class orinheritance in Java

The Existing Class is called as Super class

The New class is called as Sub Class


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Sub Classes

The Sub class is also called the child class andsuper class is also called the Parent class. InJava a child class has only one super class.

In Java all classes must be derived from someclass. The top-most class from which all otherclasses are derived is the Object class definedin java.lang package.


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Eff ect o f Sub Classes

All the Fields of Super class are available inSub Class

All the Methods of Super class are available inSub Class

All the Constructor of Super class are availablein Sub Class


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Typ es o f Sub Classes

Single

Multiple

Multi Level

Tree

Hybrid


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Single Inheritance

In case of singleinheritance there isonly a sub class and

one parent class. It isalso called singleinheritance or one levelinheritance.


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class Person{

String Name;

}

class Student extends Person{

int RollNo;

}class Single{

public static void main(String abc[]){

Student s1=new Student();s1.RollNo=1001;s1.Name="ABC";System.out.println("RollNo is "+ s1.RollNo);System.out.println("Name is "+ s1.Name);

}}


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M ulti p le Inheritance

W hen a subclass is derived from a derivedclass then this mechanism is known as themultilevel inheritance.

The derived class is called the subclass or childclass for its parent class and this parent classworks as the child class for it's just above(parent) class.


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Java does not support multiple inheritancebut the multiple inheritances can be achievedby using the interface .



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M ulti Level Inheritance

Java Does not support multiple inheritancedirectly. The mechanism of inheriting thefeatures of more than one base class into asingle class is known as multiple inheritance.

Java does not support multiple inheritancebut the multiple inheritances can be achievedby using the interface.


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M ulti Level Inheritance


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class A{

int i;}

class B extends A{

int j;}

class C extends B{

int k;}

class ML

{

public static void main(String abc[])

{

B b1=new B();

C c1=new C();

b1.j=1000;b1.i=2000;

c1.k=100;

c1.i=200;

System.out.println(b1.j);System.out.println(b1.i);

System.out.println(c1.k);

System.out.println(c1.i);

}

}


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T ree Inheritance

It is a method of inheritance where one or moresub classes is derived from common super class.

All the elements of hierarchical data model iscalled as node.

The highest level of element in the hierarchicaldata model is called as root and the lowest levelof element is called as leaves.


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T ree Inheritance

Class A

Class X

Class X1 Class X2

Class Y

Class Y1 Class Y2


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class A{

int i;}class B extends A{

int j;

}class C extends A{

int k;}

class Tree{


B b1=new B();C c1=new C();

b1.j=1000;b1.i=2000;

c1.k=100;c1.i=200;

System.out.println(b1.j);System.out.println(b1.i);

System.out.println(c1.k);System.out.println(c1.i);

}}


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H y brid Inheritance

It is a method where one or more types of inheritance are combined together and used.

This type of inheritance is combination of single, multiple, multiple and treeinheritance.


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H y brid Inheritance

Class A

Class B

Class D

Class C

Class E Class F


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class A{

int i;}class B extends A{

int j;}class C extends A

{int k;

}class D extends B{

int l;}class E extends D{

int m;}

class Hybrid{


C c1=new C();c1.k=100;c1.i=200;System.out.println(c1.k);System.out.println(c1.i);

}}


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Method Overriding

In a class hierarchy, when a method in a subclass has thesame name and type signature as a method in itssuperclass, then the method in the subclass is said tooverride the method in the super class.

W hen an overridden method is called from a subclass, Javawill always refer to method defined by the subclass. Themethod of the super class will be ignore/hidden.

In order to override any particular method of super class,the return type, method name, type and order of arguments must be identical to method of sub class.


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class A{

void Print(){System.out.println("SPIRE");}

}class B extends A{

void Print(){System.out.println("Academy");}

}

class Test{

public static void main(Stringabc[]){

B b1=new B();b1.Print();

}

}


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Am biguit y in Subclass

W e can create a method with the same namein Super Class and Sub Class.

If we want to solve this problem then we useFinal keyword.


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Am biguit y in Subclass

W e can create a method with the same namein Super Class and Sub Class. W hen we callthe method JVM execute the child classmethod.

If we want to execute the super class methodthen we can use the Super keyword.


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Constructor in Subclass

Case 1 Default Constructor

Case 2 Parameterized Constructor


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Case 1 Default ConstructorW hen we create an instance of the child class ,

JVM first call the default constructor of theSuper class then call the default constructor of the Child class


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Case 2 Parameterized ConstructorW hen we create an instance of the child class ,

JVM first call the default constructor of theSuper class then call the default constructor of the Child class

W e must Initialize all the instance variable of Super class in the child Class Constructor.



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A dvantage

Code Reusability

Implementation of Run Time PolymorphismMethod Overriding

Specialization and Generalization can beImplemented


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D isadvantage

Complexity Increase


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