Classes (Object-Oriented Programming)

This lesson covers the basics of object-oriented programming using classes in Java, so you can bundle data with shared traits together. It's for anyone searching "Java class tutorial."

Define a class with class. A constructor (a method with the same name as the class) handles initialization. Think of it like an "animal blueprint" that lets you create any number of concrete instances, like "dog" or "cat."

The example gives an Animal class name and sound fields, initializes them in the constructor, and builds a sound message in the speak() method. Notice the instance creation with new Animal("Dog", "Woof").

A common early mistake is not seeing the difference between a class and an instance. A class is a blueprint — using it in practice requires creating an instance (a concrete object) — an idea that takes some getting used to.

In real projects, this object-oriented way of thinking becomes more important the larger the application gets, and much of Java's own standard library is itself designed around classes.

📖 Reference code

class Animal {
    String name;
    String sound;
    Animal(String name, String sound) {
        this.name = name;
        this.sound = sound;
    }
    String speak() {
        return name + " says \"" + sound + "\"";
    }
}

Animal dog = new Animal("Dog", "Woof");
System.out.println(dog.speak());

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🧪 This site can't compile or run Java directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).