--- description: This tutorial covers the Class and Object definitions, Basic concepts with programming examples, Differences between object and class, and more. title: Class and Object in Java image: https://www.guru99.com/images/class-and-object-in-java.png --- [Skip to content](#main) **⚡ Smart Summary** Class and Object in Java are the core building blocks of object-oriented programming. A class is a blueprint that defines fields and methods, while an object is an instance of that class. This resource explains both concepts, their differences, and working example programs. * 🧱 **Class as Blueprint:** A class defines the fields and methods common to a particular type of object. * 🐕 **Object as Instance:** An object is a self-contained instance of a class, holding its own data and behavior. * ⚖️ **Key Difference:** A class is a template; an object is a concrete specimen created from that template. * 📐 **Design Principles:** Good classes follow SOLID principles for maintainable object-oriented code. * 💻 **Examples:** Two programs show a class with main inside and main placed in a separate class. [ Read More ](javascript:void%280%29;) ![Class and Object in Java](https://www.guru99.com/images/class-and-object-in-java.png) ## What is Classes and Objects in Java? Classes and Objects in Java are the fundamental components of OOP. Often there is confusion between classes and objects. In this tutorial, we try to tell you the difference between a Class and an Object in Java. First, let us understand what they are. ## What is Class in Java? A **Class** is a blueprint or a set of instructions to build a specific type of object. It is a basic concept of Object-Oriented Programming which revolves around real-life entities. A class in Java determines how an object will behave and what the object will contain. **Syntax of Class in Java** class { field; method; } ## What is an Object in Java? An **Object** is an instance of a class. An object in [OOP](https://www.guru99.com/java-oops-concept.html) is nothing but a self-contained component that consists of methods and properties to make a particular type of data useful. For example, color, name, table, bag, or 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 OOP can include a data structure, a variable, or a function. It has a memory location allocated. Java objects are designed as class hierarchies. **Object Syntax in Java** ClassName ReferenceVariable = new ClassName(); ## What is the Difference Between Object and Class in Java? A **Class** in object-oriented programming is a blueprint or prototype that defines the variables and the methods (functions) common to all Java objects of a certain kind. An **object** in OOP is a specimen of a class. Software objects are often used to model real-world objects that you find in everyday life. Click [here](https://www.guru99.com/faq#faq1) if the video is not accessible. Click [here](https://www.guru99.com/faq#faq1) if the video is not accessible ## Understand the concept of Java Classes and Objects with an example Let us take an example of developing a pet [management system](https://www.guru99.com/best-free-learning-management-systems.html), specially meant for dogs. You will need various information about the dogs, like different breeds of dogs, the age, size, etc. You need to model real-life beings, i.e., dogs, into software entities. [](https://www.guru99.com/images/java/052016%5F0704%5FObjectsandC1.jpg) Moreover, the million-dollar question is, how do you design such software? **Here is the solution:** First, let us do an exercise. You can see the picture of three different breeds of dogs below. [](https://www.guru99.com/images/java/052016%5F0704%5FObjectsandC2.jpg) Stop here right now! List down the differences between them. Some of the differences you might have listed out may be 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 data members for your object. [](https://www.guru99.com/images/java/052016%5F0704%5FObjectsandC3.jpg) Next, list out the common behaviors of these dogs like sleep, sit, eat, etc. So these will be the actions of our software objects. [](https://www.guru99.com/images/java/052016%5F0704%5FObjectsandC4.jpg) So far we have defined the following things: * **Class** – Dogs * **Data members** or **objects** – size, age, color, breed, etc. * **Methods** – eat, sleep, sit, and run. [](https://www.guru99.com/images/java/052016%5F0704%5FObjectsandC5.jpg) Now, for different values of data members (breed, size, age, and color) in a Java class, you will get different dog objects. [](https://www.guru99.com/images/java/052016%5F0704%5FObjectsandC6.jpg) You can design any program using this OOP approach. While creating a class, one must follow these principles: * **Single Responsibility Principle (SRP):** A class should have only one reason to change. * **Open Closed Principle (OCP):** It should be possible to extend a class without modifying it. * **Liskov Substitution Principle (LSP):** Derived classes must be substitutable for their base classes. * **Dependency Inversion Principle (DIP):** Depend on abstraction and not on concretions. * **Interface Segregation Principle (ISP):** Prepare fine-grained interfaces that are client-specific. ### RELATED ARTICLES * [Java Hello World Program ](https://www.guru99.com/java-hello-world-program.html "Java Hello World Program") * [JasperReports Tutorial: What is Jasper Report for Java? ](https://www.guru99.com/jasperreports-tutorial.html "JasperReports Tutorial: What is Jasper Report for Java?") * [Comparable vs Comparator in Java ](https://www.guru99.com/comparable-vs-comparator-java.html "Comparable vs Comparator in Java") * [Top 30 Struts Interview Questions and Answers (2026) ](https://www.guru99.com/struts-interview-questions.html "Top 30 Struts Interview Questions and Answers (2026)") ## 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 ## Java Object and Class Example: main outside class In the previous program, we created the main() method inside the class. Now, we create the class and define the main() method in another class. This is a better way than the previous one. // Class Declaration 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 class Execute { 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 This code is editable. Click Run to Compile + Execute ![]() ## FAQs 🤖 Can AI generate Java classes and objects from requirements? Yes. AI assistants can scaffold classes, fields, constructors, and methods from a plain-language description. You should still review naming, encapsulation, and logic to ensure the generated code fits your design. 🧠 How does AI use OOP classes and objects in code generation? AI models recognize class structures to generate consistent objects, suggest methods, and refactor code toward clean, object-oriented design. This accelerates development while keeping responsibilities well organized. 🏗️ What is a constructor in a Java class? A constructor is a special method that initializes a new object when it is created. It shares the same name as the class and has no return type, often setting initial field values. 🏛️ What are the four pillars of OOP in Java? The four pillars are encapsulation, inheritance, polymorphism, and abstraction. Together they structure object-oriented Java programs, promoting reusable, secure, and maintainable code built around classes and objects. #### Summarize this post with: ChatGPT Perplexity Grok Google AI **Stay Updated on AI** **Get Weekly AI Skills, Trends, Actionable Advice.** ##### Sign up for the newsletter Subscribe for Free You have successfully subscribed. 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