Classes & Objects
Understand what classes and objects are. Learn how to define a class and create object instances.
Classes & Objects is a free Java Academy lesson on CoddyKit — lesson 1 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Java Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
What is a class?
Class: A template that defines data (fields) and actions (methods). Think of it as a blueprint.
What is an object?
Object: A specific instance of a class. Each object has its own copy of the fields defined in the class.
Analogy
Analogy: A class is like a cookie cutter, and objects are the cookies made with it. One cutter, many cookies.
Why classes and objects?
Classes and objects let us organize code, reuse structure, and model real-world entities. This is the foundation of OOP.
Steps to use
Step 1: Define a class with fields and methods. Step 2: Use the new keyword to create objects. Step 3: Access fields or call methods on the object.
Demo: class and object
Code demo: define a Dog class with fields, then create Dog objects and set their data. Each object has its own state.
public class Main {
// Define a simple class inside Main for demo
static class Dog {
String name;
int age;
}
public static void main(String[] args) {
// Create two objects of Dog
Dog d1 = new Dog();
d1.name = "Buddy";
d1.age = 3;
Dog d2 = new Dog();
d2.name = "Luna";
d2.age = 5;
// Print their info
System.out.println(d1.name + " is " + d1.age + " years old.");
System.out.println(d2.name + " is " + d2.age + " years old.");
}
}
Object check
Quick check: What is an object in Java?
Recap
Recap: Classes are templates; objects are instances. You define once, create many, and each has its own state.
Frequently asked questions
Is the “Classes & Objects” lesson free?
Yes — the full text of “Classes & Objects” is free to read here on the web, and the Java Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Java Academy course, upgrade to CoddyKit PRO.
What will I learn in “Classes & Objects”?
Understand what classes and objects are. Learn how to define a class and create object instances. You practise Java Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Java Academy?
No prior experience is required. Java Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “Classes & Objects” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Java Academy lesson?
Yes. Every Java Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Classes & Objects
- Fields, Methods, Constructors
- Encapsulation (getters/setters)