Classes, Inheritance ,Packages & Interfaces in JAVA

1. Unit 2
Classes, Inheritance ,Packages &
Interfaces

2. procedure Oriented programming Object Oriented Programming
Divided Into In POP, program is divided into small
parts calledf unctions.
In OOP, program is divided into
parts called objects.
Importance In POP,Importance is not given
to data but to functions as well
as sequence of actions to be done.
(Algorithm)
In OOP, Importance is given to the
data rather than procedures or
functions because it works as a
real world.
Approach POP follows Top Down approach. OOP follows Bottom Up approach.
Access Specifiers POP does not have any access specifier. OOP has access specifiers named
Public, Private, Protected, etc.
Data Moving In POP, Data can move freely from
function to function in the system.
In OOP, objects can move and
communicate with each other
through member functions.
Data Access In POP, Most function uses Global
data for sharing that can be accessed
freely from function to function in the
system.
In OOP, data can not move easily
from function to function, it can
be kept public or private so we
can control the access of data.
Data Hiding POP does not have any proper way for
hiding data so it is less secure.
OOP provides Data Hiding so
provides more security.
Overloading In POP, Overloading is not possible. In OOP, overloading is possible in
the form of Function Overloading
and Operator Overloading.
Examples Example of POP are : C, VB, FORTRAN,
Pascal.
Example of OOP are : C++, JAVA,
VB.NET, C#.NET.

3. Class & Object
• CLASS : Represents the group of similar objects. A class binds the
data & its function together. It has 2 parts.
1.Class Definition –Member Data
2.Class function definitions- Member Functions
• An object is defined by a class
• A class is the blueprint of an object
• The class uses methods to define the behaviors of the object
• The class that contains the main method of a Java program
represents the entire program
• A class represents a concept, and an object represents the
embodiment of that concept
• Multiple objects can be created from the same class

4. Objects
• An object has:
– state - descriptive characteristics
– behaviors - what it can do (or what can be done to it)
• The state of a bank account includes its account
number and its current balance
• The behaviors associated with a bank account
include the ability to make deposits and
withdrawals
• Note that the behavior of an object might change
its state. For example: chair, pen, table, keyboard,
bike etc. It can be physical and logical.

6. DIFFERENCE BETWEEN STRUCTURE
AND CLASS
STRUCTURE CLASS
Hold only one data contains both function & data
Data members are PUBLIC
by default
Members are PRIVATE by
default
Members are easily
accessible
Not easy to access
Donot support
inheritance
Supports inheritance
no such things Members of a class can be
Private, public & private also

10. • Constructors are used to set initial values for
the object's instance variables, and to perform
other actions that need to be done before the
object is used

14. How to Create Object in Java
• Using new Keyword
• Using clone() method
• Using newInstance() method of the Class
class
• Using newInstance() method of the
Constructor class
• Using Deserialization

15. SYNTAX
ClassName object = new ClassName();

16. public class Hello
{
int x = 5;
public static void main(String[] args)
{
Hello myObj = new Hello();
System.out.println(myObj.x);
}
}

17. public class Hello
{
int x = 5;
public static void main(String[] args)
{
Hello myObj1= new Hello();
Hello myObj2= new Hello();
System.out.println(myObj.x);
}
}

18. Naming conventions

20. ACCESS SPECIFIERS
• CLASS MEMBER VISIBILITY:
1. PRIVATE : The class members(functions &
data) as private can be access only within the
class.(By default its private only)
2 . PUBLIC : Can be accessed from outside the
class
3. PROTECTED: Used in inheritance.

21. Syntax to declare a class:
class <class_name>{
data member;
method;
}
Simple Example of Object and Class
class Student1{
int id; //data member (also instance variable)
String name; //data member(also instance variable)
void getId(); //member function
public static void main(String args[]){
Student1 s1=new Student1(); //creating an object of Student
System.out.println(s1.id);
System.out.println(s1.name);
s1.getId();
}
}

22. The new keyword is used to allocate memory at runtime.
The program shows an example to insert values in a record.
Advantage of Method
•Code Reusability
•Code Optimization
new keyword

23. class Student2{
int rollno;
String name;
void insertRecord(int r, String n)
{
rollno=r;
name=n;
}
void displayInformation()
{ System.out.println(rollno+" "+name); }
public static void main(String args[])
{
Student2 s1=new Student2();
Student2 s2=new Student2();
s1.insertRecord(111,"Karan");
s2.insertRecord(222,"Aryan");
s1.displayInformation();
s2.displayInformation();
} }

24. class Box {
double width;
double height;
double depth;
}
class BoxDemo2 {
public static void main(String
args[]) {
Box mybox1 = new Box();
Box mybox2 = new Box();
double vol;
// assign values to mybox1's
instance variables
mybox1.width = 10;
mybox1.height = 20;
mybox1.depth = 15;
/* assign different values to
mybox2's
instance variables */
mybox2.width = 3;
mybox2.height = 6;
mybox2.depth = 9;
// compute volume of first box
vol = mybox1.width *
mybox1.height * mybox1.depth;
System.out.println("Volume is " +
vol);
// compute volume of second box
vol = mybox2.width *
mybox2.height * mybox2.depth;
System.out.println("Volume is " +
vol);
} }

25. // This program includes a method inside the box class.
class Box
{
double width;
double height;
double depth;
// display volume of a box
double volume()
{
System.out.print("Volume is ");
return(width * height * depth);
}
}
class BoxDemo3 {
public static void main(String args[]) {
Box mybox1 = new Box();
Box mybox2 = new Box();
double vol;
// assign values to mybox1's instance
variables
mybox1.width = 10;
mybox1.height = 20;
mybox1.depth = 15;
/* assign different values to mybox2's
instance variables */
mybox2.width = 3;
mybox2.height = 6;
mybox2.depth = 9;
// display volume of first box
vol=mybox1.volume();
System.out.println(vol);
// display volume of second box
vol=mybox2.volume();
System.out.println(vol);
}}

26. Constructors
• Constructor in java is a special type of method that
is used to initialize the object.
• Java constructor is invoked at the time of object
creation. It constructs the values i.e. provides data
for the object that is why it is known as
constructor.
Rules for creating java constructor
• Constructor name must be same as its class name
• Constructor must have no explicit return type, not
even void.

27. • Types of java constructors
There are 3 types of constructors:
• Default constructor (no-arg constructor)
• Parameterized constructor
• Copy constructor (object clone)

28. Default constructors
class Box
{ double width; double height;
double depth;
// This is the constructor for Box.
Box()
{ System.out.println("Constructing
Box");
width = 10;
height = 10;
depth = 10;
}
// compute and return volume
double volume()
{ return width * height * depth;
class BoxDemo6
{ public static void main(String args[])
{
// declare, allocate, and initialize Box
objects
Box mybox1 = new Box();
Box mybox2 = new Box();
double vol;
// get volume of first box
vol = mybox1.volume();
System.out.println("Volume is " + vol);
// get volume of second box
vol = mybox2.volume();
System.out.println("Volume is "+ vol);
} }

29. Parameterized constructor
class Box
{ double width;
double height;
double depth;
// This is the constructor for Box.
Box(double w, double h, double
d)
{ width = w; height = h; depth =
d; }
// compute and return volume
double volume()
{ return width * height * depth;
class BoxDemo {
public static void main(String args[])
{
// declare, allocate, and initialize Box
objects
Box mybox1 = new Box(10, 20, 5);
Box mybox2 = new Box(3, 6, 9);
double vol;
// get volume of first box
vol = mybox1.volume();
System.out.println("Volume is " +
vol);
// get volume of second box
vol = mybox2.volume();
System.out.println("Volume is " +
vol);

30. Copy constructor
Previous program can be extended with passing object of the class
to the constructor itself.
Eg:
Box (Box b)
{
System.out.println(“cloning object”);
}
Public static void main(String args[])
{
Box mybox1 = new Box(10, 20, 5);
Box mybox2 = new Box(mybox1);
//mybox2 is cloned from mybox1 object
}
}
Constructor with different arguments / different number of
arguments are called constructor overloading.

31. Java program to illustrate Constructor Overloading
class Box
{
double width, height, depth;
// constructor used when no dimensions specified
Box()
{
width = height = depth = 0;
}
// constructor used when cube is created
Box(double len)
{
width = height = depth = len;
}
// constructor used when all dimensions specified
Box(double w, double h, double d)
{
width = w;
height = h;
depth = d;
}
// compute and return volume
double volume()
{
return width * height * depth;
}
}
// Main code
public class Test
{
public static void main(String args[])
{
// create boxes using the various constructors
Box mybox2 = new Box();
Box mycube = new Box(7);
Box mybox1 = new Box(10, 20, 15);
double vol;
// get volume of first box
vol = mybox1.volume();
System.out.println(" Volume of mybox1 is " + vol);
// get volume of second box
vol = mybox2.volume();
System.out.println(" Volume of mybox2 is " + vol);
// get volume of cube
vol = mycube.volume();
System.out.println(" Volume of mycube is " + vol);
}
}

32. Method Overloading
• If a class have multiple methods by same name but
different parameters, it is known as Method
Overloading.
• Method overloading increases the readability of the
program.
• 2 ways to differentiate the methods which are
overloaded
1.by number of arguments
2.by data types

33. 1)Example of Method Overloading by
changing the no. of arguments
class Calculation
{
void sum(int a,int b)
{System.out.println(a+b);}
void sum(int a,int b,int c)
{System.out.println(a+b+c);}
public static void main(String args[])
{
Calculation obj=new Calculation();
obj.sum(10,10,10);
obj.sum(20,20);
} }

34. 2)Example of Method Overloading by
changing data type of argument
class Calculation2
{
void sum(int a,int b)
{System.out.println(a+b);}
void sum(double a,double b)
{System.out.println(a+b);
}
public static void main(String args[]) {
Calculation2 obj=new Calculation2();
obj.sum(10.5,10.5);
obj.sum(20,20);
} }

35. //Write a program to find area of geometrical
figures using method overloading.

36. import java.util.*;
class geofig
{
double area(double r)
{
return(3.14*r*r);
}
float area(float s)
{
return(s*s);
}
float area(float l,float b)
{
return(l*b);
}
double area(double b,double
h)
{ return(0.5*b*h);
public static void main(String arg[])
{
Scanner sc =new Scanner(System.in);
geofig g = new geofig();
System.out.println("enter the value for radius of
circle");
double r =sc.nextDouble();
System.out.println("area of circle="+g.area(r));
System.out.println("enter the value for side of a
square");
float s =sc.nextFloat();
System.out.println("area of square="+g.area(s));
System.out.println("enter the value for length and
breadth of rectangle");
float l =sc.nextFloat();
float b =sc.nextFloat();
System.out.println("area of rectangle="+g.area(l,b));
System.out.println("enter the value for base & height
of triangle");
double b1 =sc.nextDouble();
double h =sc.nextDouble();
System.out.println("area of triangle="+g.area(b1,h));
}
}

37. Lab 8:
import java.util.*;
class GarbageCollection
{ public static void main(String s[]) throws Exception
{ Runtime rs = Runtime.getRuntime();
System.out.println("Total memory is: " +
rs.totalMemory());
System.out.println("Free memory in JVM before
Garbage Collection = "+rs.freeMemory());
rs.gc();
System.out.println("Free memory in JVM after
Garbage Collection = "+rs.freeMemory()); } }

38. Access Specifier

40. Java Command Line Arguments
• The java command-line argument is an
argument i.e. passed at the time of running
the java program.
• The arguments passed from the console can
be received in the java program and it can be
used as an input.

41. class CommandLineExample{
public static void main(String args[]){
System.out.println("Your first argument is:
"+args[0]);
}
}

42. keyword

44. final keyword
• The final keyword in java is used to restrict the
user. The java final keyword can be used in
many context
For example, when a variable is declared with the "final" keyword, its value
cannot be changed once it is set:
final int a = 10;
a = 20; // this will result in a compile-time error

45. the keyword "abstract" is used to
declare an abstract class or method.
Here's an example of an abstract class:
abstract class Shape { abstract double area();
}
• An abstract method is a method that is
declared in an abstract class, but does not
have a body. The purpose of an abstract
method is to specify a method signature that
must be implemented by any concrete
subclasses of the abstract class.

46. • Finalize Keyword in java:
• The finalize method in java is called by the
garbage collector before an object is garbage
collected.