Inheritance

A class can extend another class, inheriting its fields and methods and adding or overriding its own.

class Animal {
    String name;

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

    void makeSound() {
        System.out.println(name + " makes a sound");
    }
}

class Dog extends Animal {
    Dog(String name) {
        super(name); // calls Animal's constructor
    }

    @Override
    void makeSound() {
        System.out.println(name + " barks");
    }
}

Dog rex = new Dog("Rex");
rex.makeSound(); // Rex barks

super(name) calls the parent class's constructor — it must be the first statement in a subclass constructor if used at all.

Common mistakes

• Forgetting @Override on an overriding method. It's not required, but without it a typo'd method name silently creates a brand-new, unrelated method instead of the compiler catching the mistake.
• Java only supports single inheritance — a class can extend only one other class (though it can implement many interfaces).

Practice

Create a Cat class extending Animal that overrides makeSound() to print "<name> meows".

class Cat extends Animal {
    Cat(String name) {
        super(name);
    }

    @Override
    void makeSound() {
        System.out.println(name + " meows");
    }
}