Inheritance

A class can inherit from another with extends, automatically getting access to its fields and methods. super(name) inside a subclass's constructor calls the parent class's constructor, which is required before the subclass constructor can do anything else when the parent has no no-argument constructor.

Overriding with @Override

Marking a method @Override tells the compiler you intend to replace the parent class's version — it's optional, but it catches real mistakes, like a typo'd method name that would otherwise silently define a brand-new method instead of overriding the one you meant to. dog.speak() calls Dog's own version, not Animal's, because Dog overrides it.

public class Main {
    static class Animal {
        String name;

        Animal(String name) {
            this.name = name;
        }

        String speak() {
            return name + " makes a sound";
        }
    }

    static class Dog extends Animal {
        Dog(String name) {
            super(name);
        }

        @Override
        String speak() {
            return name + " barks";
        }
    }

    public static void main(String[] args) {
        Dog dog = new Dog("Rex");
        System.out.println(dog.speak());
    }
}

Rex barks

Next: polymorphism and interfaces — Java's first-class way of describing shared behavior across unrelated classes.