Explain class and object with example.

What is Class in Java?

Class are a blueprint or a set of instructions to build a specific type of object. It is a basic concept of Object-Oriented Programming which revolve around the real-life entities. Class in Java determines how an object will behave and what the object will contain.

Syntax

class <class_name>{  
    field;  
    method;  
  }  

What is Object in Java?

Object is an instance of a class. An object in OOPS is nothing but a self-contained component which consists of methods and properties to make a particular type of data useful. For example color name, table, bag, barking. When you send a message to an object, you are asking the object to invoke or execute one of its methods as defined in the class.

From a programming point of view, an object in OOPS can include a data structure, a variable, or a function. It has a memory location allocated. Java Objects are designed as class hierarchies.

Syntax

ClassName ReferenceVariable = new ClassName();

Only For Understanding Not For Write In exam Above

Classes and Objects in Java Example Programs

// Class Declaration
public class Dog {
    // Instance Variables
    String breed;
    String size;
    int age;
    String color;

  
    // method 1
    public String getInfo() {
        return ("Breed is: "+breed+" Size is:"+size+" Age is:"+age+" color is: "+color);
    }
    

    public static void main(String[] args) {
        Dog maltese = new Dog();
        maltese.breed="Maltese";
        maltese.size="Small";
        maltese.age=2;
        maltese.color="white";
        System.out.println(maltese.getInfo());
    }
}

Output:

Breed is: Maltese Size is:Small Age is:2 color is: white

Understand the concept of Java Classes and Objects with an example.

Let's take an example of developing a pet management system, specially meant for dogs. You will need various information about the dogs like different breeds of the dogs, the age, size, etc.

You need to model real-life beings, i.e., dogs into software entities.

Moreover, the million dollar question is, how you design such software?

Here is the solution-

First, let's do an exercise.

You can see the picture of three different breeds of dogs below.

Stop here right now! List down the differences between them.

Some of the differences you might have listed out maybe breed, age, size, color, etc. If you think for a minute, these differences are also some common characteristics shared by these dogs. These characteristics (breed, age, size, color) can form a data members for your object.

Next, list out the common behaviors of these dogs like sleep, sit, eat, etc. So these will be the actions of our software objects.

So far we have defined following things,

• Class - Dogs
• Data members or objects- size, age, color, breed, etc.
• Methods- eat, sleep, sit and run.

Now, for different values of data members (breed size, age, and color) in Java class, you will get different dog objects.

You can design any program using this OOPs approach.