Class and Object in Java

Classes and objects are fundamental concepts of object-oriented programming in Java. They are used to define and create objects, which are instances of classes, to model real-world entities and their behaviors. A class in Java is a blueprint or a template that defines the structure and behavior of objects. It is a blueprint for creating objects with specific properties (data members) and methods (functions). These created instances can access any methods within a class inside the main method.

A simple class consists of the following:

Data member
constructor
method
nested class
interface

public class Dog {
  
     String name;
   int age;
    
   public void bark() {
       System.out.println("Woof!");
   }
   
   public void run() {
       System.out.println("The dog is running.");
   }
}

Here is a simple class Dog with name and age initialized with this return data type.
We then create two methods, bark() and run().

On the other hand, an object is an instance of a class. It is created using the new keyword followed by the class name and can be assigned to a variable.

For this example:

Dog doggy = new Dog();

This is how we create objects for a class.
Now, we can access everything inside the class Dog using the doggy object.

Dog doggy = new Dog(); 
doggy.name = "Buddy"; 
doggy.age = 3; 
doggy.bark();

We set the name and age properties of the object and then call the bark() method on the object.

Output:

Woof!

Conclusion:

Objects allow you to create multiple class instances, each with its properties and behaviors. You can create and use objects of a class in your Java programs to model real-world entities, encapsulate data and behavior, and create reusable code.