1. Programming in Java Text Books :
Herbert Schildt, “JAVA 2: Complete Reference”, 5th Edition, TMH
Reference Books :
Jim Keogh, “J2EE Complete Reference”.
Kenarnold and James gosling : “The Java Programming Language”.

2. Inheritance, Interfaces and Packages
Programming in Java
Inheritance, Interfaces and Packages
1. Inheritance
2. Extending Classes, Overriding Methods
3. Final variables and Methods
4. Abstract Methods and Classes
5. Visibility control.
6. Interfaces and Packages
7. Multiple Inheritance
8. Creating and Executing Programs

3. Inheritance
Inheritance :is a mechanism in which one object acquires all the properties and behaviors of parent object.
The idea behind inheritance is that you can create new classes that are built upon existing classes.
When you inherit from an existing class, you can reuse methods and fields of parent class, and you can add new methods and fields also.
Inheritance represents the IS-A relationship, also known as parent-child relationship.
Why use inheritance…?
For Method Overriding (so runtime polymorphism can be achieved).
For Code Reusability.

4. Inheritance Inheritance Syntax
The extends keyword indicates that you are making a new class that derives from an existing class.
A class that is inherited is called a super class.
The new class is called a subclass.
class Subclass-name extends Superclass-name  
{  
   //methods and fields  
}  
class Employee {  
 float salary=40000;  
}  
class Programmer extends Employee {  
int bonus=10000;  
  public static void main(String args[]){  
    Programmer p=new Programmer();  
System.out.println("Programmer salary is:"+p.salary);  
    System.out.println("Bonus of Programmer is:"+p.bonus);   }

5. class A {
int i, j
void showij() {
System.out.println(“ i and j : “ + i + j); } }
class B extends A {
int k;
void showk() { System.out.println(“ k : “ + k); }
void sum() { System.out.println(“sum : “+(i+j+k));
class SimpleInheritance {
public static void main (string[] args) {
A superOb = new A();
B subOb = new B();
superOb.i = 10; superOb.j = 20; subOb.k=15;
superOb.showij();
subOb.showk();
subOb.sum();

6. Multiple And Hybrid Inheritance Is Supported Through Interface Only
Types of Inheritance
Single
Multiple
Tree/Hierarchical
Multi-level
Hybrid
Multiple And Hybrid Inheritance Is Supported Through Interface Only

7. Aggregation
If a class have an entity reference, it is known as Aggregation. Aggregation represents HAS-A relationship.
Consider a situation, Employee object contains many informations such as id, name, Id etc. It contains one more object named address, which contains its own informations such as city, state, country, zipcode etc. as given below.
class Employee{  
int id;  
String name;  
Address address; //Address is a class  
...   }
For Code Reusability.
class Address {  
int Hno;  
String City,State,Country;
int Zipcode;   }

8. Aggregation class Operation { int square(int n){ return n*n; } }
class Circle{
Operation op; //aggregation
double pi=3.14;
double area(int radius) {
op=new Operation();
int rsquare= op.square(radius); //code reusability
return pi*rsquare;
public static void main(String args[]){
Circle c=new Circle();
double result=c.area(5);
System.out.println(result);

9. Overriding Methods
If subclass (child class) has the same method as declared in the parent class, it is known as method overriding in java. (or)
If subclass provides the specific implementation of the method that has been provided by one of its parent class, it is known as method overriding.
Usage of Java Method Overriding
Method overriding is used to provide specific implementation of a method
that is already provided by its super class.
Method overriding is used for runtime polymorphism
Rules for Java Method Overriding
method must have same name as in the parent class
method must have same parameter as in the parent class.
must be IS-A relationship (inheritance).

10. Overriding Methods class Vehicle{
void run() { System.out.println("Vehicle is running"); } }
class Bike2 extends Vehicle{
void run() { System.out.println("Bike is running safely"); }
public static void main(String args[]) {
Bike2 obj = new Bike2();
obj.run();

11. Real time Example for overriding Methods

12. Real time Example for overriding Methods
class Bank{   int getRateOfInterest() { return 0; }   }  
class SBI extends Bank{   int getRateOfInterest() { return 8; }   }  
class ICICI extends Bank{  int getRateOfInterest() { return 7; }   }  
class AXIS extends Bank{   int getRateOfInterest() { return 9; }   }  
class Test2{  
public static void main(String args[]){  
SBI s=new SBI();  
ICICI i=new ICICI();  
AXIS a=new AXIS();  
System.out.println("SBI Rate of Interest: "+s.getRateOfInterest());  
System.out.println("ICICI Rate of Interest: "+i.getRateOfInterest());  
System.out.println("AXIS Rate of Interest: "+a.getRateOfInterest());  
}   }

13. Abstract Class in java Example: abstract class A{}
A class that is declared with abstract keyword.
It can have abstract and non-abstract methods (method with body)
Abstraction is a “process of hiding the implementation details and showing
only functionality to the user“.
There are two ways to achieve abstraction in java
Abstract class (0 to 100%)
Interface (100%)
Example: abstract class A{}
abstract method : A method that is declared as abstract and does not have implementation is known as abstract method.
abstract void printStatus();

14. Abstract Class in java abstract class Bike{
   abstract void run(); //no body and abstract   
}     
class Honda4 extends Bike{  
void run(){
System.out.println("Running safely..");
public static void main(String args[]){  
Bike obj = new Honda4();  
 obj.run();  
Running safely….

15. Abstract Class in java drawing circle abstract class Shape {
abstract void draw(); }
class Rectangle extends Shape{
void draw() { System.out.println("drawing rectangle"); }
class Circle1 extends Shape{
void draw() { System.out.println("drawing circle"); }
class TestAbstraction1{
public static void main(String args[]){
Shape s=new Circle1();
s.draw();
drawing circle

16. Abstract Class in java Rate of Interest is: 7 % abstract class Bank{
abstract int getRateOfInterest(); }
class SBI extends Bank{
int getRateOfInterest() { return 7; }
class PNB extends Bank{
class TestBank{
public static void main(String args[]){
Bank b=new SBI(); //if object is PNB, method of PNB will be invoked
int interest=b.getRateOfInterest();
System.out.println("Rate of Interest is: "+interest+" %");
Rate of Interest is: 7 %

17. Abstract class having constructor, data member, methods etc
abstract class Bike {
Bike() { System.out.println("bike is created"); } // Constructor
abstract void run();
void changeGear() { System.out.println("gear changed"); } }
class Honda extends Bike{
void run() { System.out.println("running safely.."); }
class TestAbstraction2{
public static void main(String args[]) {
Bike obj = new Honda();
obj.run();
obj.changeGear();
bike is created
running safely..
gear changed

18. Java Package
A java package is a group of similar types of classes, interfaces and sub-packages.
Package in java can be categorized in two form,
built-in package and user-defined package.
There are many built-in packages such as java, lang, awt, javax, swing, net, io, util, sql etc.
Advantage of Java Package
1) Java package is used to categorize the classes and interfaces so that they can be easily maintained.
2) Java package provides access protection.
3) Java package removes naming collision.

19. Java Package

20. Java Package
How to run java package program – fqn (Fully Qualified Name)
e.g. mypack.Simple etc to run the class.
To Compile: javac -d . Simple.java
To Run: java mypack.Simple
Output: Welcome to package
The -d is a switch that tells the compiler where to put the class file
i.e. it represents destination.
The . represents the current folder.
How to access package from another package?
There are three ways to access the package from outside the package.
import package.*;
import package.classname;
fully qualified name.

21. Example of package that import the packagename.*
Java Package
Example of package that import the packagename.*
package pack;  
public class A{
public void msg() { System.out.println("Hello");}   }
Javac A.java
package mypack;
import pack.*;
class B{
public static void main(String args[]){
A obj = new A();
obj.msg(); }
Javac B.java
Output : Hello

22. Example of package that import the packagename.classname
Java Package
Example of package that import the packagename.classname
package pack;  
public class A{
public void msg() { System.out.println("Hello");}   }
Javac A.java
package mypack;
import pack.A;
class B{
public static void main(String args[]){
A obj = new A();
obj.msg(); }
Javac B.java
Output : Hello

23. Example of package that import the packagename using fqn
Java Package
Example of package that import the packagename using fqn
package pack;  
public class A{
public void msg() { System.out.println("Hello");}   }
Javac A.java
package mypack;
import pack.A;
class B{
public static void main(String args[]){
pack.A obj = new pack.A();;
obj.msg(); }
Javac B.java
Output : Hello

24. Java Package Example of package HelloMoon.java HelloWorld.java
package world.moon;
public class HelloMoon {
private String holeName = "rabbit hole";
public String getHoleName() {
return holeName; }
public void setHole() {
this.holeName = holeName; } }
HelloMoon.java
pakage world;
public class HelloWorld {
public HelloWorld(){
System.out.println("Hello World Package"); }
void getValue(){
System.out.println("The Value 5"); } }
HelloWorld.java

25. Java Package Example of package TestPack.java import world.moon.*;
public class TestPack{
public static void main(String[] args) {
HelloMoon HM =new HelloMoon();
HM.setHole();
System.out.println("getHoleName = "+HM.getHoleName());
HelloWorld HW = new HelloWorld();
HW.getValue(); }
TestPack.java
Output:
getHoleName = rabbit hole
Hello World Package
The Value

26. Access Modifiers in Java
There are two types of modifiers in java
access modifiers and non-access modifiers.
The access modifiers in java specifies accessibility (scope) of a data member, method, constructor or class.
There are 4 types of java access modifiers:
Private : accessible only within class
Default : accessible only within package
Protected : accessible within/outside the package but through Inheritance only
Public : accessible everywhere

27. Access Modifiers in Java
Private : accessible only within class.
class A{
private A(){}
private int data=40;
public void msg(){ System.out.println("Hello java"); } }
public class Simple{
public static void main(String args[]){
A obj=new A();
System.out.println(obj.data);
obj.msg();
} .
//Compile Time Error
//Compile Time Error
//Compile Time Error

28. Access Modifiers in Java
The default modifier is accessible only within package.
//save by A.java  
package pack;  
class A{  
void msg() { System.out.println("Hello"); }   }
//save by B.java  
package mypack;  
import pack.*;  
class B{  
  public static void main(String args[]){  
   A obj = new A();  
   obj.msg();
  }   }
//Compile Time Error 
//Compile Time Error 

29. Access Modifiers in Java
The protected modifier is accessible outside package but through inheritance.
//save by A.java  
package pack;
public class A{
protected void msg() { System.out.println("Hello"); } }
//save by B.java  
package mypack;
import pack.*;
class B extends A{
public static void main(String args[]){
B obj = new B();
obj.msg(); }
Output : Hello

30. Access Modifiers in Java
The public modifier is accessible anywhere.
//save by A.java  
package pack;
public class A{
public void msg() { System.out.println("Hello"); } }
//save by B.java  
package mypack;
import pack.*;
class B{
public static void main(String args[]){
A obj = new A();
obj.msg(); }
Output : Hello

31. Interfaces in Java
It is a blueprint of a class. It has static constants and abstract methods only.
There can be only abstract methods in the java interface, but not method body.
It is used to achieve fully abstraction and multiple inheritance in Java.
Java Interface also represents IS-A relationship.
It cannot be instantiated just like abstract class.
In other words, Interface fields are public, static and final bydefault, and methods are public and abstract.
Why use Java interface?
There are mainly three reasons to use interface. They are given below.
It is used to achieve fully abstraction.
By interface, we can support the functionality of multiple inheritance.
It can be used to achieve loose coupling.

32. Interfaces in Java
Interface fields are public, static and final by default, & methods are public and abstract.

33. Example of Interfaces in Java
interface printable {
void print(); }
class A6 implements printable {
public void print() { System.out.println("Hello"); }
public static void main(String args[]) {
A6 obj = new A6();
obj.print();
Output:Hello

34. Multiple Inheritance in Java
If a class implements multiple interfaces, or an interface extends multiple interfaces i.e. known as multiple inheritance.

35. Multiple Inheritance in Java
interface Printable {
void print(); }
interface Showable {
void show();
class A7 implements Printable,Showable {
public void print() { System.out.println("Hello"); }
public void show() { System.out.println("Welcome"); }
public static void main(String args[]){
A7 obj = new A7();
obj.print();
obj.show();
Output:Hello
Welcome

36. Interface Inheritance in Java
interface Printable {
void print(); }
interface Showable extends Printable{
void show();
class Testinterface2 implements Showable{
public void print() { System.out.println("Hello"); }
public void show() { System.out.println("Welcome"); }
public static void main(String args[]){
Testinterface2 obj = new Testinterface2();
obj.print();
obj.show();
Hello Welcome

37. Points to remember for nested interfaces
An interface i.e. declared within another interface or class is known as nested interface.
The nested interfaces are used to group related interfaces so that they can be easy to maintain.
The nested interface must be referred by the outer interface or class.
It can't be accessed directly.
Points to remember for nested interfaces
Nested interface must be public if it is declared inside the interface but it can have any access modifier if declared within the class.
Nested interfaces are declared static implicitly.

38. Nested Interface
Syntax of nested interface which is declared within the interface
interface interface_name{
...
interface nested_interface_name{ }
class class_name{
...
interface nested_interface_name{ }

39. Output:hello nested interface
Nested Interface – Example-1
interface Showable {
void show();
interface Message{
void msg(); }
class TestNestedInterface1 implements Showable.Message{
public void msg() { System.out.println("Hello nested interface"); }
public static void main(String args[]){
Showable.Message message=new TestNestedInterface1(); //upcasting here
message.msg();
Output:hello nested interface

40. Output:hello nested interface
Nested Interface – Example-2
class A{
interface Message{
void msg(); }
class TestNestedInterface2 implements A.Message{
public void msg() { System.out.println("Hello nested interface"); }
public static void main(String args[]){
A.Message message=new TestNestedInterface2(); //upcasting here
message.msg();
Output:hello nested interface

41. Difference between Abstract class and Interface
Abstract class achieves partial abstraction (0 to 100%)
Interface achieves fully abstraction (100%).

42. Difference between Abstract class and Interface
interface A{ //Creating interface that has 4 methods
void a(); //bydefault, public and abstract
void b(); void c(); void d(); }
//Creating abstract class that provides the implementation of one method of A interface
abstract class B implements A { public void c() { System.out.println("I am C"); } }
//Creating subclass of abstract class, now we need to provide the implementation of rest of the methods class M extends B{
public void a() { System.out.println("I am a"); }
public void b() { System.out.println("I am b"); }
public void d() { System.out.println("I am d"); }
//Creating a test class that calls the methods of A interface
class Test5{
public static void main(String args[]){
A a=new M();
a.a(); a.b(); a.c(); a.d(); } }
Output
I am a
I am b
I am c
I am d