Classes in Java great learning.pdf

Class in Java
Proprietary content. ©Great Learning. All Rights Reserved. Unauthorized use or distribution prohibited

Agenda
• Introduction to a Class
• Requirement of a Class
• Elements of a Class
• Defining a Class
• Memory allocation
• Coding standards for Classes
• Access modifiers used for Classes
• Encapsulation
• Example programs for Class creation
• Inner Class

Introduction to Class

Introduction to Class
• User-defined data type
• Representation of an object-oriented approach
• Process of binding data members and methods in a single unit
• No implementation is possible without classes in java
• Example

Requirement of a Class

Requirement of Class
• Everything is treated as an object in an object-oriented programming language
• The class provides meaning to the objects
• Enhancements become easy
• Maintainability and Modularity will be improved

Elements of a Class

Elements of a class
Classes consist of the following:-
• Methods/Behaviors
They are methods that decides the action/task be performed by
the object
• Variables/Attributes
They are the data members that an object consists of.
• In real scenarios class is represented using a Class diagram created using UML concepts and
software

Defining a class

Defining a Class
Following is the syntax followed for defining a class in java:-
class <name_of_the_class>
{
//variable declaration
//methods declaration
}
It’s a keyword in java

Memory Allocation

Memory Allocation
• Java classes have logical existence
• Defining a class doesn’t allocate memory space.
• Memory space is created only when objects are created.

Coding standards for Classes

Coding standards for Classes
Some specific coding standards are followed for defining a class in java
1. Starting letter should be in capitals. If the class name consists of more than one word then first
letter of each word should be in capitals (camel case is followed)
2. White spaces are not allowed in the class name
3. Letters, digits, dollar signs, and underscores can be used
4. Choosing a full name in place of cryptic abbreviations is a good programming practice
5. Avoid using java keywords as the name of the class

Coding Concepts related to Classes
• We always run a java class
• For every class, one .class file is created
• The main method of a corresponding class is executed, if the main method is not present it
throws a Runtime error
• Highly recommended to take one class for the source file and the name of the source file and
name of the class should be the same

Access modifiers used for Classes

Access modifiers used for classes
The applicable modifiers for top level class are:-
• public
• <default>
• final
• abstract
• strictfp
Inner Class applicable modifiers are :-
• Private
• Protected
• Static

Public:-
If a class is declared public, it can be accessed from anywhere.
Default:-
It is a by default used access specifier in java. If a class is declared default then that class can be
accessed only within that package
Final:-
If a class is declared final, then that class cannot be inherited
Abstract:-
A class is declared as abstract then its instantiation is not possible.

Private:-
Only an inner class can be declared private and a private inner class can be accessed only within the
outer class
Protected:-
If an inner class is declared as protected then it can be accessed only within the outer class and its
child class
Static:-
A class cannot be declared as static but for inner classes, it can be used
strictfp:-
A class is declared as strictfp then all its methods should follow IEEE754 standards

Encapsulation

Encapsulation
It is the method of encapsulating the functions and data members into a single unit.
Every java class and package is an encapsulated component.
Example:-
class bank
{
String bankName;
void printName()
{
System.out.println(“name of bank is State bank of india”);
}
}
Encapsulated
component

Question

Question
• Defining a class in java
 Let’s write a class definition for a student who has his name, roll no, and marks of three subjects.
 The class student should have two methods to calculate the total marks of a student and get the
grades
• Accessing the defined methods and variables
 Create an object of the class to call the methods and access the data members inside the main
method

Inner Class

Inner Class
• It’s a way to declare a class inside another class
• When there is no chance of a existence of an object without an existence of another object then we
use the inner class concept.
• The relationship between outer and inner class is a has-a relationship
Example:-
Without Bank there can’t be a Account. So,
class Bank
{
class Account
{
}
}

Inner Class
• Inside inner class, static member should not be declared.
• How will .class file be created and executed for these inner classes?
class Bank
{
class Account
{
}
public static void main(String[] args)
{
System.out.println(“account created”);
}
}

Inner Class
Accessing Inner class from the static area of outer class.
public class Bank
{
class Account
{
public void printAccountName()
{
System.out.println(“Bank account name is abcd”);
}
}
{
Bank b = new Bank();
Bank.Account a = b.new Bank();
a.printAccountName();
} } Proprietary content. ©Great Learning. All Rights Reserved. Unauthorized use or distribution prohibited

Inner Class
Accessing Inner class from the instance area of outer class.
public class Bank
{
class Account
{
{
}
}
public void callingMethod()
{
Account a = new Account();
a.printAccountName();
}

Continued…
{
Bank b = new Bank();
b.callingMethod();
}
}
• Nesting of the inner class is also possible
Class A
{
class B
{
class C
{ //codes and functionalities
}
}

Anonymous inner class
• For one-time usage of an inner class, we create an anonymous inner class.
• It’s an inner class without a name
• There are 3 types of anonymous inner class
• Anonymous inner class that extends a class
• Anonymous inner class that implements an interface
• Anonymous inner class that is defined inside arguments

Anonymous inner class that extends a class
public class Bank
{
{
}
class Account
{
{
Bank b1 = new Bank()
{
{
System.out.println(“Bank account name is xyz”);
}
};
b1.printAccountName();
Bank b2 = new Bank();
b2.printAccountName();
}
}
Inner
class
definition
Calling the methods
defined inside inner
class

Summary

Summary
Discussed the following topics:-
1. What is a class and how to define a class in java
2. The different coding guidelines and standards to be followed for
classes in java
3. Different access modifiers suitable for classes at different levels
4. Class is the best example to implement encapsulation
5. The complete concept of inner classes and it’s implementations
6. Examples related to classes.

Classes in Java great learning.pdf

Recommended

Recommended

More Related Content

Similar to Classes in Java great learning.pdf

Similar to Classes in Java great learning.pdf (20)

Recently uploaded

Recently uploaded (20)

Classes in Java great learning.pdf