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Class and Object in Java - The Complete Guide

Classes and Objects in Java

Classes in Java

It is basically a collection of objects. It is a template which creates objects that defines its state and behavior. A class contains field and method to define the state and behavior of its object.
Syntax for Declaring Class:

<Access_Modifier> class <Class_Name>

Where,
Class_Name: It describes the class name which defines by using class keyword.
Access_Modifier : It defines the scope of the data member, method or class i.e.  who can access class and members of the class. There are three access modifiers in java:

  • Public – Accessible everywhere
  • Default – Accessible only within the package. If you not using any modifier then default is considered
  • Private – Accessible only within the class
  • Protected – Accessible within package and outside the package but during inheritance only 

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Example

public class Fruit{
String name;  // field
String color;  // field
void vitamin(){  // method
}
void taste(){  // method
}
}

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Learn how to use the Super Keyword in Java to access the methods and variables of the parent class!

Objects in Java

An object is an instance of a class. Class and Objects has state and behavior. For example a fruit has states – name, color and behaviors – vitamin, taste
Syntax
Keyword new is used to create object of class.

<Class_Name>   Object_Name = new <Class_Name>();

Example

Fruit f = new Fruit ();

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To access the method of class use the following syntax:

f.taste();

Example

public class Addition{
int sum;
public void total(int a, int b){
sum = a + b;
System.out.println("Addition of two numbers:" +sum );
}
public static void main(String []args){
Addition add = new Addition ();
add.total(10, 20);
}
}

Output
Addition of two numbers: 30

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About the Author

Senior Consultant Analytics & Data Science

Presenting Sahil Mattoo, a Senior Consultant Analytics & Data Science at Eli Lilly and Company is an accomplished professional with 14 years of experience across data science, analytics, and technical leadership domains, demonstrates a remarkable ability to drive business insights. Sahil holds a Post Graduate Program in Business Analytics and Business Intelligence from Great Lakes Institute of Management.