Java Classes and Objects Explained – Syntax, Constructors & Real Examples

Introduction – Building Blocks of Java OOP

In Java, everything revolves around classes and objects. Think of a class as a blueprint (like a design plan) and an object as a real-world item built from that blueprint.

By the end of this article, you’ll understand:

• What Java classes and objects are
• How to create and use them
• Fields, methods, and constructors inside a class
• Real-world examples and OOP integration

What is a Class in Java?

A class is a user-defined blueprint that defines fields (variables) and methods (functions) which describe the behavior and state of an object.

Basic Syntax:

public class Car {
    String model;
    int year;

    void drive() {
        System.out.println(model + " is driving.");
    }
}

Explanation:

• Car is a class
• It has two fields: model, year
• One method: drive()

What is an Object in Java?

An object is an instance of a class. It contains actual values stored in the variables and can call the methods defined in the class.

Creating an Object:

Car myCar = new Car();

Explanation:

• myCar is an object created using new
• It has its own copy of model, year, and can call drive()

Assigning Values & Using Methods

myCar.model = "Tesla Model Y";
myCar.year = 2023;
myCar.drive();

Output:

Tesla Model Y is driving.

Object fields are accessed using dot (.) notation.

Class with Constructor

A constructor initializes objects when they are created.

public class Car {
    String model;
    int year;

    // Constructor
    public Car(String m, int y) {
        model = m;
        year = y;
    }

    void display() {
        System.out.println(model + " - " + year);
    }
}

Create and Use the Object:

Car car1 = new Car("Toyota", 2022);
car1.display();  // Output: Toyota - 2022

Multiple Objects of the Same Class

Car car1 = new Car("BMW", 2020);
Car car2 = new Car("Audi", 2021);

car1.display();  // BMW - 2020
car2.display();  // Audi - 2021

Each object has its own copy of fields but shares the class structure.

Real-World Analogy

Class vs Object – Quick Comparison

Best Practices with Java Classes & Objects

Tips:

• Use PascalCase for class names (StudentRecord)
• Use camelCase for object names (myCar)
• Encapsulate fields using private and expose via getters/setters
• Keep each class in its own .java file for clarity

Avoid:

• Making fields public unless absolutely necessary
• Using multiple responsibilities in one class (violates SRP)

Summary

Classes and objects are the foundation of Java’s object-oriented model. You define the blueprint with a class, and build actual usable data structures with objects.

Key Takeaways:

• Class defines structure (fields + methods)
• Object is an actual instance of the class
• Use constructors to initialize fields
• Create multiple objects from the same class for different data sets

FAQs – Java Classes and Objects

What is a class in Java?

A class is a blueprint for creating objects that contain fields and methods.

How is an object different from a class?

A class is a definition; an object is a real instance that holds actual data.

Can a class have multiple objects?

Yes, you can create as many objects from a class as needed.

What is the default value of an object in Java?

Uninitialized object references point to null by default.

Are constructors mandatory in a class?

No. If not provided, Java provides a default no-argument constructor automatically.