Java Inheritance
Inheritance lets one class take on the fields and methods of another. Instead of rewriting shared code, you build a general parent class and let more specific child classes extend it, adding only what makes them different.
Parent and child classes
In Java you create inheritance with the extends keyword. The class being extended is called the superclass (or parent), and the class doing the extending is the subclass (or child). The child automatically gains every non-private member of the parent, then adds its own.
- The parent class holds the shared, general code.
- The child class uses extends to inherit that code.
- The child can add new fields and methods of its own.
- The child can override a parent method to change its behavior.
Extending a class
// Parent class
class Animal {
String name;
public void eat() {
System.out.println(name + " is eating.");
}
}
// Child class inherits from Animal
class Dog extends Animal {
public void bark() {
System.out.println(name + " says woof!");
}
}
public class Main {
public static void main(String[] args) {
Dog d = new Dog();
d.name = "Rex";
d.eat(); // inherited from Animal
d.bark(); // defined in Dog
}
}A child class often needs to build on the parent's constructor. The super keyword calls the parent's constructor, letting the parent set up its own fields before the child adds to them.
Using super
class Vehicle {
String brand;
public Vehicle(String brand) {
this.brand = brand;
}
}
class Car extends Vehicle {
int doors;
public Car(String brand, int doors) {
super(brand); // call the parent constructor first
this.doors = doors;
}
public static void main(String[] args) {
Car c = new Car("Honda", 4);
System.out.println(c.brand + " with " + c.doors + " doors");
// Outputs: Honda with 4 doors
}
}Exercise: Java Inheritance
Which keyword does a Java class use to inherit from another class?
