Understand the idea

Inheritance lets a subclass extend a superclass. Use it for a meaningful is-a relationship and understand what behavior can be overridden. Composition is often clearer when one object simply uses another rather than being a specialized version of it.

Explore the details

Java Inheritance

Inheritance lets a child class automatically gain all the attributes and methods of a parent class. Write common code once in the parent — all children get it for free.

The extends Keyword

Code anatomy / கோடின் விளக்கம்

• Subclass / child — the class that inherits. Uses extends.
• Superclass / parent — the class being inherited from.
• Use protected on parent attributes so child classes can access them.
• Use final class to prevent any class from extending it.

class Animal {
    String name;
    void eat() { System.out.println(name + " eats."); }
}

class Dog extends Animal {
    @Override
    void eat()  { System.out.println(name + " eats dog food."); }
    void bark() { System.out.println(name + " says: Woof!"); }
}

Dog d = new Dog();
d.name = "Rex";
d.eat();   // Rex eats dog food.
d.bark();  // Rex says: Woof!

// Parent reference holds child object
Animal a = new Dog();
a.name = "Buddy";
a.eat();   // Buddy eats dog food. (runtime type = Dog)

A complete runnable example

This complete Main.java program focuses on the lesson idea. Reference fragments above may demonstrate individual statements; this example includes the imports, entry point, and supporting types it needs.

public class Main {
    public static void main(String[] args) throws Exception {
        Dog dog = new Dog();
        dog.eat();
        dog.bark();
    }
}
class Animal { void eat() { System.out.println("Eating"); } }
class Dog extends Animal { void bark() { System.out.println("Woof"); } }

Eating
Woof

Change it. Run it. Understand it.

Load this lesson example into the editor. Change one value or statement, predict the result, then press RUN to execute Java.

Make it your own

Your learning checkpoint

• Explain the example without reading the output first.
• Make the change requested in the practice task.
• Describe why the result changed—or why compilation failed.

Ready to move on? Follow the next lesson in course order, or return to the curriculum to review a prerequisite.