Exploring Key Difference Between Class and Object in Java

The main difference between class and object in Java is that a class serves as a template for creating objects with shared attributes and behaviours. While objects are tangible instances that adhere to the structure and behaviour defined by the class.

Java is a versatile and widely-used programming language. It relies heavily on the concept of classes and objects. To learn and use Java properly, you must first grasp the essential difference between class and object in Java. 

Do explore What is Java?

Comparison Table: Class vs Object in Java

Aspect	Class	Object
Definition	A class is a blueprint or template for creating objects.	An object is a specific instance of a class.
Syntax	Declared using the class keyword followed by the class name.	Created using the new keyword followed by the class constructor.
Purpose	Defines the structure and behavior of objects.	Represents a real-world entity based on the class blueprint.
Usage	Contains class variables (fields) and methods that are shared by all instances of the class.	Represents a unique instance with its own attribute values and can invoke methods defined in the class.
Examples	java public class Car { // Class variables and methods go here }	java Car myCar = new Car(); // Creates an instance of the Car class
Memory Allocation	Class definitions are stored in the method area of the JVM.	Objects are dynamically allocated memory in the heap at runtime.
Accessibility	Can be public, private, or protected, determining visibility from other classes.	Accessed within the scope of their declaration, following encapsulation principles.
Lifecycle	Exists throughout the execution of a program.	Created, used, and eventually destroyed by the JVM’s garbage collector.

What is a Class in Java?

At its core, a class in Java serves as a blueprint or template for creating objects. It encapsulates attributes (data) and behaviours (methods) that define the characteristics of objects belonging to that class. 

Think of it as a set of instructions for constructing something. For instance, if we were building a car, the class would be a detailed design plan.

What is an Object in Java?

Now, let’s shift our focus to objects. 

In Java, an object is an instance of a class. It’s a tangible, real-world manifestation of the class’s blueprint. 

Continuing with our car analogy, an object would be a specific car built according to the design specified in the class.

Relationship between Class and Object in Java

To understand their relationship better, consider this classes define the structure, while objects represent instances of that structure. Classes are like architectural blueprints, and objects are the buildings constructed based on those blueprints. You can create multiple objects from a single class, each with its own unique characteristics.

Differences in Declaration and Usage – Class and Object in Java

Here, we delve into the nitty-gritty details of how classes and objects are declared and used in Java. 

When declaring a class, you employ the ‘class’ keyword, while objects are created using the ‘new’ keyword. 

Classes define variables and methods, whereas objects access and manipulate those variables and methods.

Differences in Memory Allocation – Class and Object in Java

Java manages memory allocation differently for classes and objects. Class definitions are stored in the method area of the Java Virtual Machine (JVM). On the other hand, objects are dynamically allocated memory in the heap at runtime. 

Think of the method area as a library of blueprints and the heap as the construction site for objects.

Differences in Accessibility – Class and Object in Java

Accessibility is a key differentiator. Classes can be public, private, or protected, which determines their visibility and accessibility from other classes. 

Objects, on the other hand, are accessed within the scope of their declaration. This concept of encapsulation ensures that the inner workings of a class are hidden from the outside world.

Differences in Lifecycle – Class and Object in Java

Both classes and objects have distinct lifecycles. A class exists throughout the execution of a program. It’s like a constant presence in the background, always ready to serve. 

Objects, however, are created, used, and eventually destroyed by the Java Virtual Machine’s garbage collector. They come into existence when needed and are cleaned up when they’re no longer required.

How are classes and objects related in object-oriented programming?

Classes and objects are the building blocks of object-oriented programming (OOP). Classes serve as blueprints for objects, allowing you to create multiple instances with shared characteristics and behaviours. OOP promotes code reusability, modularity, and a structured approach to programming.