Inheritance: extends, super, and overriding · ⁨Pewarisan: extends, super, dan overriding⁩

English

Inheritance: building on a class

Inheritance lets one class reuse another class's fields and methods.
The class you build on is the superclass (parent); the new class is the subclass (child).
A subclass is-a kind of its superclass: a Dog is an Animal.

Bahasa Indonesia

Pewarisan: membangun di atas kelas

Pewarisan memungkinkan satu kelas menggunakan ulang field dan method dari kelas lain.
Kelas yang Anda bangun di atasnya adalah superclass (induk); kelas baru adalah subclass (anak).
Subclass merupakan jenis dari superclass-nya: sebuah Dog adalah Animal.

Superclass Hewan; Anjing dan Kucing masing-masing memperluasinya dan menimpa speak()

English

`extends` and `super`

Write class Dog extends Animal to make Dog a subclass of Animal.
Dog automatically gets every public method of Animal, like getName().
The subclass constructor calls the superclass constructor first with super(...).

Bahasa Indonesia

`extends` dan `super`

Tulis class Dog extends Animal untuk membuat Dog subclass dari Animal.
Dog secara otomatis menerima semua public method dari Animal, seperti getName().
Konstruktor subclass memanggil konstruktor superclass terlebih dahulu dengan super(...).

public class Main {
    public static void main(String[] args) {
        Dog d = new Dog("Rex");
        System.out.println(d.getName());   // Rex   (inherited from Animal)
        System.out.println(d.speak());     // Woof  (Dog's own version)
    }
}

class Animal {
    private String name;
    public Animal(String name) { this.name = name; }
    public String getName() { return this.name; }
    public String speak() { return "some sound"; }
}

class Dog extends Animal {
    public Dog(String name) {
        super(name);          // run Animal's constructor
    }
    public String speak() {   // override Animal's speak()
        return "Woof";
    }
}

English

Overriding a method

A subclass can override an inherited method: give it the same signature, a new body.
Dog's speak() replaces Animal's speak() for Dog objects.
Methods it does not override (like getName()) are still inherited unchanged.

Bahasa Indonesia

Menimpa method

Subclass dapat menimpa method yang diwarisi: berikan tanda tangan yang sama, body baru.
Dog's speak() menggantikan Animal's speak() untuk objek Dog.
Method yang tidak ia timpa (seperti getName()) tetap diwariskan tanpa perubahan.

English

`super.method()` — extend, don't replace

Sometimes you want the parent's work plus a little more.
Inside an override, super.describe() runs the superclass version of the method.
Then you add to its result instead of rewriting it from scratch.

Bahasa Indonesia

`super.method()` — perluas, jangan ganti

Terkadang Anda ingin pekerjaan induk ditambah sedikit lagi.
Di dalam penimpangan, super.describe() menjalankan versi superclass dari method tersebut.
Kemudian Anda menambahkan ke hasilnya alih-alih menulisnya dari awal.

public class Main {
    public static void main(String[] args) {
        Bird b = new Bird("Tweety");
        System.out.println(b.describe());
        // I am an animal named Tweety, and I can fly
    }
}

class Animal {
    private String name;
    public Animal(String name) { this.name = name; }
    public String describe() { return "I am an animal named " + this.name; }
}

class Bird extends Animal {
    public Bird(String name) { super(name); }
    public String describe() {
        return super.describe() + ", and I can fly";   // reuse, then add
    }
}

English

is-a: a subclass fits where its superclass is expected

Because a Dog is an Animal, you can write Animal a = new Dog("Spot");.
The variable's type is Animal, but the object is really a Dog.
This "is-a" rule is what makes the next lesson — polymorphism — possible.

Bahasa Indonesia

is-a: subclass pas di mana superclass diharapkan

Karena Dog adalah Animal, Anda bisa menulis Animal a = new Dog("Spot");.
Tipe variabel adalah Animal, tetapi objek sebenarnya adalah Dog.
Aturan "is-a" inilah yang membuat pelajaran berikutnya — polimorfisme — mungkin.

English

Common mistakes

super(...) must be the first line of a subclass constructor.
Add @Override so the compiler catches a wrong signature.

Bahasa Indonesia

Kesalahan umum

super(...) harus menjadi baris pertama dari constructor subclass.
Tambahkan @Override agar compiler menangkap tanda tangan yang salah.

English

Now you try

Each task gives you a finished Animal superclass. Write or complete the subclass below it.
A hidden Harness builds your object and checks both inherited and new behaviour.
Press Run to compile, then Check answer. Your code runs on the server, so even the first run is fast.

Bahasa Indonesia

Sekarang Anda coba

Setiap tugas memberikan superclass Animal yang sudah jadi. Tulis atau lengkapi subclass di bawahnya.
Harness tersembunyi membuat objek Anda dan memeriksa perilaku yang diwarisi serta yang baru.
Tekan Run untuk kompilasi, lalu Check answer. Kode Anda berjalan di server, sehingga bahkan run pertama pun cepat.

Below the finished Animal, write a class Cat that extends Animal. Give it a constructor Cat(String name) that passes the name up with super(name). Add nothing else — Cat should inherit getName() for free. · ⁨Di bawah class selesai Animal, buatlah class Cat yang extends Animal. Berikan constructor Cat(String name) yang meneruskan nama ke atas dengan super(name). Tambahkan tidak ada lagi — Cat harus mewarisi getName() secara gratis.⁩

// Animal is written for you. Do not change it.
class Animal {
    private String name;
    public Animal(String name) { this.name = name; }
    public String getName() { return this.name; }
    public String speak() { return "some sound"; }
    public String describe() { return "I am an animal named " + this.name; }
}

// TODO: write a class Cat that extends Animal.
//   - constructor Cat(String name) that calls super(name)
//   - nothing else: Cat inherits getName() for free

Click Run to see the output here. · ⁨Klik Jalankan untuk melihat output di sini.⁩

Complete the class Cow (it already extends Animal). Override speak() so a Cow returns "Moo" instead of the default. getName() must still work (inherited). · ⁨Lengkapi class Cow (sudah extends Animal). Override speak() sehingga saat dipanggil pada Cow akan mengembalikan "Moo" alih-alih nilai default. getName() tetap harus berfungsi (warisan).⁩

// Animal is written for you. Do not change it.
class Animal {
    private String name;
    public Animal(String name) { this.name = name; }
    public String getName() { return this.name; }
    public String speak() { return "some sound"; }
    public String describe() { return "I am an animal named " + this.name; }
}

class Cow extends Animal {
    public Cow(String name) {
        super(name);
    }

    // TODO: override speak() so a Cow returns "Moo"
}

Click Run to see the output here. · ⁨Klik Jalankan untuk melihat output di sini.⁩

Complete the class Fish (it already extends Animal). Override describe() so it returns the Animal description plus ", and I can swim". Reuse the parent's work by calling super.describe() — do not rewrite the whole sentence. · ⁨Lengkapi class Fish (sudah extends Animal). Override describe() agar mengembalikan deskripsi Animal ditambah ", and I can swim". Gunakan kembali kerja induk dengan memanggil super.describe() — jangan tulis ulang seluruh kalimat.⁩

// Animal is written for you. Do not change it.
class Animal {
    private String name;
    public Animal(String name) { this.name = name; }
    public String getName() { return this.name; }
    public String speak() { return "some sound"; }
    public String describe() { return "I am an animal named " + this.name; }
}

class Fish extends Animal {
    public Fish(String name) {
        super(name);
    }

    // TODO: override describe() to return super.describe() + ", and I can swim"
}

Click Run to see the output here. · ⁨Klik Jalankan untuk melihat output di sini.⁩

Inheritance: extends, super, and overriding · ⁨Pewarisan: extends, super, dan overriding⁩

Inheritance: building on a class

Pewarisan: membangun di atas kelas

`extends` and `super`

`extends` dan `super`

Overriding a method

Menimpa method

`super.method()` — extend, don't replace

`super.method()` — perluas, jangan ganti

is-a: a subclass fits where its superclass is expected

is-a: subclass pas di mana superclass diharapkan

Common mistakes

Kesalahan umum

Now you try

Sekarang Anda coba

Handout · ⁨Lembar Kerja⁩

Log in or create account · ⁨Masuk atau buat akun⁩

Your subject · ⁨Mata Pelajaran Anda⁩

All sections · ⁨Semua bagian⁩

Feedback & help · ⁨Umpan balik & bantuan⁩

Inheritance: extends, super, and overriding · ⁨Pewarisan: extends, super, dan overriding⁩

Inheritance: building on a class

Pewarisan: membangun di atas kelas

extends and super

extends dan super

Overriding a method

Menimpa method

super.method() — extend, don't replace

super.method() — perluas, jangan ganti

is-a: a subclass fits where its superclass is expected

is-a: subclass pas di mana superclass diharapkan

Common mistakes

Kesalahan umum

Now you try

Sekarang Anda coba

`extends` and `super`

`extends` dan `super`

`super.method()` — extend, don't replace

`super.method()` — perluas, jangan ganti