The document provides an overview of classes and objects in Java, explaining that Java is an object-oriented, class-based programming language that allows for multi-threading. It defines key concepts such as the distinction between classes (blueprints) and objects (instances), their properties (state, behavior, identity), and how to create classes and objects, along with methods, encapsulation, and command line arguments. Additionally, it illustrates the syntax for creating classes and objects, accessing their members, and handling command line arguments in Java applications.

1. JAVA
Creating
Classes & Objects
Command line arguments

2. Topics for Today’s Session
About JAVA
Creating Classes and Objects
Command line arguments
How to Create class and Object

3. Java
 Java is a computing platform for application
development and an object-oriented,
 Java is Class-based and Concurrent programming
language
 It means the code can be executed by multiple
processes at the same time.
 Java can run on all platforms and free to access.
 Java is Simple, Secure, Robust, Complete Object
oriented and Platform Independent High level
Language
 It is Portable and Multi-thread technology gives
High Performance.

4. Objects and Classes in Java
 An object in Java is the physical as well as a logical entity, whereas, a class in Java is a
logical entity only.
 An entity that has state and behavior is known as an object e.g., chair, bike, pen, table,
car, etc.
 It can be physical or logical (tangible and intangible). The example of an intangible
object is the banking system.
 An object consists of :
 State : It is represented by attributes of an object. It also reflects the properties of
an object.
 Behavior : It is represented by methods of an object. It also reflects the response of
an object with other objects.
 Identity : An object identity is typically implemented via a unique ID. The value of the ID is not
visible to the external user. However, it is used internally by the JVM to identify each object
uniquely.
For Example, Pen is an object. Its name is Reynolds; color is Blue, known as its state. It is used to write,
so writing is its behavior.
Identity
Name of Dog
State / Attributes
Breed
Color
Age
Behaviours
Bark
Eat
Sleep
Bite

5.  An object is an instance of a class. A class is a template or blueprint from
which objects are created. So, an object is the instance(result) of a class.
Object Definitions:
 An object is a real-world entity.
 An object is a runtime entity.
 The object is an entity which has state and behavior.
 The object is an instance of a class.

6. Class
 A class is a group of objects which have common properties.
 It is a template or blueprint from which objects are created.
 It is a logical entity. It can't be physical.
 Class is a a collection of the data items and functions. The data items are called
as fields and function are called as methods.
 Java is said to be true object oriented programming language because without
class we cannot do anything.
 A class in Java can contain:
 Fields
 Methods
 Constructors
 Blocks
 Nested class and interface

7. Create a Class
 To create a class, use the keyword class:
 A class defines the state and behavior of the program components known
as objects.
 Classes create objects and objects use methods to communicate between
them. Methods are just like functions.
 The instance of the class is said to be object. Class variable is said to be
object.
 A class is a user-defined data type serves to define properties.
 Once a class is defined we can create variables of that type using
declarations.
 Example: Create a class named "MyClass" with a variable a:
Class classname [extends superclassname]
{
[variable/field declaration];
[methods declaration];
}
class MyClass
{
int a = 5;
}
Here
Everything inside the brackets is optional.
classname and superclassname are any valid java identifiers.
The keyword extends indicate that the properties of the superclass name are
extended to the classname class.
This concept is known as Inheritance.

8. Fields declaration:
 Data is encapsulated in a class by placing data fields in the class. These variables
are called “instance variables”.
 These are declared just as local variables;
Methods Declaration:
 A class with only data fields has no life. Such classes cannot respond to any
messages.
 We must add methods that are useful for manipulating the data of the class.
 Methods for a class are declared inside the body of the class but immediately after
the declaration of the variables.
Type methodname (parameter list)
{
method_body;
}
Method declaration having four parts:
1. The name of the method ( method name) (It is
any valid identifier)
2. The type of the value of the method returns
(type) (it is any valid data type, it is void when it
does not return any value.)
3. A list of parameters (parameter list) (This list
contains variable names and types of all the values
we want to send as input, when no input data are
required, we must use empty parentheses)
4. The body of the method. It describes the
operations to be performed on the data.
Example: : int sum (int a, int b)
{
c=a+b;
return c;
Method in Java
 In Java, a method is like a
function which is used to
expose the behavior of an
object.
 Advantage of Method
 Code Reusability
 Code Optimization

9. A class can contain any of the following variable types.
Local variables Variables defined inside methods, constructors or
−
blocks are called local variables.
The variable will be declared and initialized within the
method and the variable will be destroyed when the method has
completed.
Instance variables Instance variables are variables within a class
−
but outside any method.
 These variables are initialized when the class is instantiated.
 Instance variables can be accessed from inside any method,
constructor or blocks of that particular class.
 Instance variable doesn't get memory at compile time.
 It gets memory at runtime when an object or instance is created.
That is why it is known as an instance variable.
Class variables Class variables are variables declared within a
−
class, outside any method, with the static keyword.

10. Example
class Dog {
String breed;
int age;
String color;
void barking() {
}
void hungry() {
}
void sleeping() {
}
}
Creating Objects:
 An object is a block of memory that contains space to store all the instance
variables.
 An object is a software entity (unit) that combines a set of data with set of
operations to manipulate that data.
 A class defines a type of object. i.e., each object belongs to some class object is
also called as an instance.
 Java has an operator new to create objects. Creating an object is also referred
to as instantiating an object.
 Objects in java can be created by using the syntax.
Syntax:
Classname objname;
Objname = new classname();
 The first statement declares a variable to hold
the object reference and second one actually
assigns the object reference to the variable.
 Ex
triangle tri1; // declaring the object)
Tri1 = new triangle //instantiating the object)
The above two statements are combined into a
single statement as
Triangle tri1 = new triangle();

11. Accessing class Members: every object contains its own set of variables.
 We should assign values to these variables in order to use them in our
program.
 When we are outside the class we cannot access the instance variables and
methods directly. For this we use dot operator.
objectname.varaiblename = value;
objectname.methodname (parameter list);
Example: tri1.length = 15;
tri2.length = 20;
tri1.getData( 20,30)
public class MyClass {
int a = 5;
public static void main(String[] args) {
MyClass myObj = new MyClass();
System.out.println(myObj.a);
}
}

12. Ex: A javaprogramtodemonstrateapplicationofclasses, objectsandmethods.(Pra.Prog. 17)
classtriangle {
intlength,width;
voidgetData(intx, inty)
{
length= x;
width= y;
}
int triarea( )
{
intarea= (length*width)/2;
return(area);
}
}
classtriarea {
publicstatic voidmain (Stringargs[ ])
{
int area1, area2;
triangletri1= newtriangle();
triangletri2= newtriangle();
tri1.length= 20;
tri1.width=30;
area1=( tri1.length*tri1.width)/2;
tri2.getData( 10, 15);
area2=tri2.triarea();
System.out.println( "area1= "+area1);
System.out.println( "area2= "+area2);
}
}
Instance variables declared in a single
line
getData is a method, it does not return any value
so its type is void, we are passing two integer
values and they are assigned to length and width
triarea is another method, it returns a value of
data type int. We are not passing values, so
the parameter list is empty
class with main method
Creating objects
Accessing variables
Accessing Methods

13. Command line Arguments
 The java command-line argument is an argument i.e. passed at the time of
running the java program.
 A Java application can accept any number of arguments from the command line.
 The String array stores all the arguments passed through the command line.
 Arguments are always stored as strings and always separated by white-space.
// Example using Commandline arguments
class Cmdargs {
public static void main(String[] args) {
System.out.println("Command-Line arguments are");
// loop through all arguments
for(String str: args) {
System.out.println(str);
}
} }
1. To compile the code
javac Cmdargs.java
2. To run the code
java Cmdargs
Now suppose we want to pass some arguments
while running the program,
we can pass the arguments after the class name. For
example,
java Main apple ball cat
output.
Command-Line arguments are
Apple
Ball
Cat

14. // Program to check for command line arguments
class Hello {
public static void main(String[] args) {
// check if length of args array is greater than 0
if (args.length > 0) {
System.out.println("The command line"+ " arguments are:");
// iterating the args array and printing the command line arguments
for (String s:args)
System.out.println(s);
}
else
System.out.println("No command line "+
"arguments found.");
} }
javac Hello.java
java Hello Lion Dog Cat Elephant
Output:
The Command-Line arguments are
Lion
Dog
Cat
Elephant
javac Hello.java
java Hello
Output
No Command-Line arguments foun

15. Summary
 In this lesson you learnt about
 What is class and Object?
 How to create Class in java?
 How to creabjte Oects in java
 Command line arguments