The document provides information about classes and objects in Java. It discusses what a class is, class naming conventions, members of a class including fields and methods, declaring objects, allocating memory to objects using the new keyword, instance variables, instance methods, and some examples. Specifically: - A class is a blueprint from which individual objects are created. Class names follow camel casing conventions. - Members of a class include fields (properties) and methods (behaviors). Fields can be primitives or references, methods define object interactions. - To declare an object, use the class name and object name (e.g. Person p1). The new keyword allocates memory and returns a reference to the new

1. Simple class and object examples
in Java
Presented By Harish Gyanani

2. What is class?
A class is a blue print from which individual
objects are created.

3. Class naming convention
• By convention, class names capitalize the
initial of each word.
• For example:
Employee, Boss, DateUtility, PostOffice, Regula
rRateCalculator.

4. What are members of Class?
• Field:
– field is nothing but the property of the class or object
which we are going to create .
– Example if we are creating a class called computer then
they have property like model, memSize, hdSize, osType
etc.
• Method:
– method is nothing but the operation that an object can
perform it define the behavior of object how an object can
interact with outside world.
– Example startMethod (), shutdownMethod ().

5. Fields in class
1.Fields are variables.
2.They can be primitives or references
to objects.
For example, the Employee class has
two fields, age and salary.
public class Employee
{
int age;
int salary
}

6. Fields Naming Conventions

7. Fields Naming Conventions
1.Field names should follow the camel naming
convention.

8. Fields Naming Conventions
1.Field names should follow the camel naming
convention.
2.The initial of each word in the field, except for
the first word, is written with a capital letter.

9. Fields Naming Conventions
1.Field names should follow the camel naming
convention.
2.The initial of each word in the field, except for
the first word, is written with a capital letter.
3.For example: age, maxAge, address,
validAddress, numberOfRows.

10. Instance variables
Variables within a class but outside any method.

11. Instance Methods
Methods defined in a class which is only
accessible through the Object of the class are
called Instance methods.

12. Example: Person Class
class Person
{
String name;
int age;
}

13. Example: Person Class
class Person
{
String name;
int age;
}
Without
methods

14. class
keyword
Example: Person Class
class Person
{
String name;
int age;
}
Without
methods

15. class
keyword
Example: Person Class
class Person
{
String name;
int age;
}
Name of class
Without
methods

16. class
keyword
Example: Person Class
class Person
{
String name;
int age;
}
Name of class
Without
methods
Start of
class

17. class
keyword
Example: Person Class
class Person
{
String name;
int age;
}
Name of class
Without
methods
Start of
class
End of
class

18. class
keyword
Example: Person Class
class Person
{
String name;
int age;
}
End of
class
Data members of class
with default
access(instance variable)
Name of class
Without
methods
Start of
class

19. How to declare object?

20. How to declare object?
Person p1;

21. How to declare object?
Person p1;
//declare reference to object

22. How to declare object?
Person p1;
//declare reference to object
//Syntax: <classname> <objectname>

23. How to declare object?
Person p1;
//declare reference to object
//Syntax: <classname> <objectname>
• It is simply a variable that can refer to an
object.

24. How to declare object?
Person p1;
//declare reference to object
//Syntax: <classname> <objectname>
• It is simply a variable that can refer to an
object.
Person p1;
null
p1

25. Allocate memory

26. Allocate memory
p1 = new Person();

27. Allocate memory
p1 = new Person();
//allocate a Person object

28. Allocate memory
p1 = new Person();
//allocate a Person object
//Syntax: <objectname> = new <classname>();

29. Allocate memory
p1 = new Person();
//allocate a Person object
//Syntax: <objectname> = new <classname>();
• The new operator dynamically allocates (that is, allocates at
run time) memory for an object and returns a reference to it.

30. Allocate memory
p1 = new Person();
//allocate a Person object
//Syntax: <objectname> = new <classname>();
• The new operator dynamically allocates (that is, allocates at
run time) memory for an object and returns a reference to it.
• This reference is, the address in memory of the object
allocated by new.

31. Allocate memory
p1 = new Person();
//allocate a Person object
//Syntax: <objectname> = new <classname>();
• The new operator dynamically allocates (that is, allocates at
run time) memory for an object and returns a reference to it.
• This reference is, the address in memory of the object
allocated by new.
name
p1 = new Person();
p1
age
Person object

32. Combination of these statements

33. Combination of these statements

34. Combination of these statements

35. Combination of these statements

36. Combination of these statements
Person p1 = new Person();

37. Combination of these statements
Person p1 = new Person();
//Syntax: <classname> <objectname> = new <classname>();

38. public class for Person class
public class NewClass1
{
public static void main(String args[])
{
Person obj1 = new Person();
obj1.name=“ramesh";
obj1.age=22;
int a=obj1.age;
System.out.println(a);
System.out.println(obj1.name);
}
}

39. public class for Person class
public class NewClass1
{
public static void main(String args[])
{
Person obj1 = new Person();
obj1.name=“ramesh";
obj1.age=22;
int a=obj1.age;
System.out.println(a);
System.out.println(obj1.name);
}
}
Instance variables
are initialized with
object name
qualifier

40. public class for Person class
Instance variables
are initialized with
object name
qualifier
public class NewClass1
{
public static void main(String args[])
{
Person obj1 = new Person();
obj1.name=“ramesh";
obj1.age=22;
int a=obj1.age;
System.out.println(a);
Syntax to set value in
System.out.println(obj1.name);
instance variable:}
}
<objectname>.<variablename> = <value>;

41. public class for Person class
Instance variables
are initialized with
object name
qualifier
public class NewClass1
{
public static void main(String args[])
{
Person obj1 = new Person();
obj1.name=“ramesh";
obj1.age=22;
int a=obj1.age;
System.out.println(a);
Syntax to set value in
System.out.println(obj1.name);
instance variable:}
} Syntax to get value
<objectname>.<variablename> = <value>;
from instance
variable:<variable> = <objectname>.<instance_variable_name>

42. Complete Program
public class NewClass1
{
public static void main(String args[])
{
Person obj1 = new Person();
obj1.name=“ramesh";
obj1.age=22;
int a=obj1.age;
System.out.println(a);
System.out.println(obj1.name);
}
}
class Person
{
String name;
int age;
}

43. Output

44. Example 1: Dog Class
class Dog
{
String breed;
int age;
String color;
Instance variables
void barking() {}
void hungry() {}
void sleeping() {}
}
In this example,
barking(), hungry() and
sleeping() are instance
methods.

45. Example 2: Stock class
Class Stock
{
public commodity;
public price;
public void buy (int no_of commodity) {}
public boolean sale () {}
}

46. Example 2: Stock class
Class Stock
{
public commodity;
public price;
Instance variables
public void buy (int no_of commodity) {}
public boolean sale () {}
}

47. Example 2: Stock class
Class Stock
{
public commodity;
public price;
Instance variables
public void buy (int no_of commodity) {}
public boolean sale () {}
}
In this
example, buy(), and
sale() are instance
methods.

48. Example 2: Stock class
Class Stock
{
public commodity;
public price;
Instance variables
public void buy (int no_of commodity) {}
public boolean sale () {}
}
Collectively, the methods
and variables defined
within a class are
called members of the
class.
In this
example, buy(), and
sale() are instance
methods.

49. Example 3: Person Class
class Person
{
private String name;
private int age;
public void getData()
{
Scanner sc = new Scanner(System.in);
System.out.println("Enter name and age");
name=sc.nextLine();
age=sc.nextInt();
}
public void display()
{
System.out.println("Name ="+name);
System.out.println("Age ="+age);
}
}

50. Example 3: Person Class
class Person
{
private String name;
private int age;
public void getData()
{
Scanner sc = new Scanner(System.in);
System.out.println("Enter name and age");
name=sc.nextLine();
age=sc.nextInt();
}
public void display()
{
System.out.println("Name ="+name);
System.out.println("Age ="+age);
}
}
With
methods

51. Example 3: Person Class
class Person
{
private String name;
private int age;
Private instance variables cannot be
accessed outside the class
public void getData()
{
Scanner sc = new Scanner(System.in);
System.out.println("Enter name and age");
name=sc.nextLine();
age=sc.nextInt();
}
public void display()
{
System.out.println("Name ="+name);
System.out.println("Age ="+age);
}
}
With
methods

52. Example 3: Person Class
class Person
{
private String name;
private int age;
Private instance variables cannot be
accessed outside the class
public void getData()
{
Scanner sc = new Scanner(System.in);
System.out.println("Enter name and age");
name=sc.nextLine();
age=sc.nextInt();
}
public void display()
{
System.out.println("Name ="+name);
System.out.println("Age ="+age);
}
}
With
methods
getData() and
display() instance
methods are
public and can be
accessed outside
the class.

53. Example 3: Person Class
class Person
{
private String name;
private int age;
Private instance variables cannot be
accessed outside the class
public void getData()
{
Scanner sc = new Scanner(System.in);
System.out.println("Enter name and age");
name=sc.nextLine();
age=sc.nextInt();
}
public void display()
{
System.out.println("Name ="+name);
System.out.println("Age ="+age);
}
}
With
methods
getData() and
display() instance
methods are
public and can be
accessed outside
the class.
Methods inside class can access
private data of class. In this case
getData() and display() methods
are accessing private data.

54. They are
defined inside
class not
inside method
Example 3: Person Class
class Person
{
private String name;
private int age;
Private instance variables cannot be
accessed outside the class
public void getData()
{
Scanner sc = new Scanner(System.in);
System.out.println("Enter name and age");
name=sc.nextLine();
age=sc.nextInt();
}
public void display()
{
System.out.println("Name ="+name);
System.out.println("Age ="+age);
}
}
With
methods
getData() and
display() instance
methods are
public and can be
accessed outside
the class.
Methods inside class can access
private data of class. In this case
getData() and display() methods
are accessing private data.

55. public class code for Person class
public class abc
{
public static void main(String args[])
{
Person p1 = new Person();
p1.getData();
p1.display();
}
}
NOTE: getData()
and Display()
method cannot be
called without
object qualifier.

56. public class code for Person class
public class abc
{
public static void main(String args[])
{
Person p1 = new Person();
p1.getData();
p1.display();
}
}
Qualifier
: Object
name
NOTE: getData()
and Display()
method cannot be
called without
object qualifier.

57. public class code for Person class
public class abc
{
public static void main(String args[])
{
Person p1 = new Person();
p1.getData();
p1.display();
}
}
Dot operator
NOTE: getData()
and Display()
method cannot be
called without
object qualifier.

58. public class code for Person class
public class abc
{
public static void main(String args[])
{
Person p1 = new Person();
p1.getData();
p1.display();
}
}
Instance method
because it is called
using object
NOTE: getData()
and Display()
method cannot be
called without
object qualifier.

59. public class code for Person class
public class abc
{
public static void main(String args[])
{
Person p1 = new Person();
p1.getData();
p1.display();
}
}
Qualifier
: Object
name
Instance method
because it is called
using object
Dot operator
NOTE: getData()
and Display()
method cannot be
called without
object qualifier.

60. Complete program
import java.util.Scanner;
class Person
{
private String name;
private int age;
public class abc
{
public static void main(String args[])
{
Person p1 = new Person();
}
public void getData()
}
{
Scanner sc = new Scanner(System.in);
System.out.println("Enter name and age");
name=sc.nextLine();
age=sc.nextInt();
}
public void display()
{
System.out.println("Name ="+name);
System.out.println("Age ="+age);
}
}
p1.getData();
p1.display();

61. Complete program
import java.util.Scanner;
class Person
{
private String name;
private int age;
public class abc
{
public static void main(String args[])
{
Person p1 = new Person();
}
public void getData()
}
{
Scanner sc = new Scanner(System.in);
System.out.println("Enter name and age");
name=sc.nextLine();
age=sc.nextInt();
}
public void display()
{
System.out.println("Name ="+name);
System.out.println("Age ="+age);
}
}
p1.getData();
p1.display();
A program can contain multiple
classes but only one public
class(same name as file name)
and contains main method

62. Complete program
import java.util.Scanner;
class Person
{
private String name;
private int age;
public class abc
{
public static void main(String args[])
{
Person p1 = new Person();
p1.getData();
p1.display();
}
public void getData()
}
{
Scanner sc = new Scanner(System.in);
System.out.println("Enter name and age");
name=sc.nextLine();
age=sc.nextInt();
}
public void display()
{
System.out.println("Name ="+name);
System.out.println("Age ="+age);
}
}
Creating and instantiating
Person class object p1.
A program can contain multiple
classes but only one public
class(same name as file name)
and contains main method

63. Complete program
import java.util.Scanner;
class Person
{
private String name;
private int age;
public class abc
{
public static void main(String args[])
{
Person p1 = new Person();
p1.getData();
p1.display();
}
public void getData()
}
{
Scanner sc = new Scanner(System.in);
System.out.println("Enter name and age");
name=sc.nextLine();
age=sc.nextInt();
}
public void display()
{
System.out.println("Name ="+name);
System.out.println("Age ="+age);
}
}
Creating and instantiating
Person class object p1.
A program can contain multiple
classes but only one public
class(same name as file name)
and contains main method
Calling instance
methods of
Person Class using
p1 object.

64. Output

65. Members of class

66. Members of class
Members of
class

67. Members of class
Members of
class
Data
members

68. Members of class
Members of
class
Data
members
Methods

69. Members of class
Members of
class
Data
members
Instance data
members
Methods

70. Members of class
Members of
class
Data
members
Instance data
members
Static data
members/
Class
Variables
Methods

71. Members of class
Members of
class
Data
members
Instance data
members
Static data
members
Methods
Instance
methods

72. Members of class
Members of
class
Data
members
Instance data
members
Static data
members
Methods
Instance
methods
Static
methods/
Class methods

73. Class diagram in UML

74. Class diagram in UML
UML class is represented by the diagram shown below. The diagram is
divided into four parts:-

75. Class diagram in UML
UML class is represented by the diagram shown below. The diagram is
divided into four parts:•The top section is used to name the class.

76. Class diagram in UML
UML class is represented by the diagram shown below. The diagram is
divided into four parts:•The top section is used to name the class.
•The second one is used to show the attributes of the class.

77. Class diagram in UML
UML class is represented by the diagram shown below. The diagram is
divided into four parts:•The top section is used to name the class.
•The second one is used to show the attributes of the class.
•The third section is used to describe the operations performed by the
class.

78. Variable Types
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
instantiated when the class is loaded. Instance variables
can be accessed from inside any method, constructor or
blocks of that particular class.
• Class variables: Class variables are variables declared with
in a class, outside any method, with the static keyword.