Object Superclass
Learning Targets:
- What is the Object class
- Why is the Object class important to remember
Every class and object created without the extends
keyword will be implicitly extended from the Object Superclass. This means it will inherit some basic methods. Some notable methods are:
getClass()
toString()
equals()
So What?
Well its important to keep in mind when writing out your class. If you are planning to have a method in your class/object that matches the basic Object, then it must be a public override
because all of the Object methods are public.
- are some methods from Object such as getClass() that you cannot override.
// this will return an error
class Shape {
String toString(){
return "Shape";
}
}
// this will be fine
class Shape{
@Override
public String toString(){
return "Shape";
}
}
Popcorn Hacks
Create an example where you execute an unchanged method from Object, then execute a different method from Object that you changed.
class Animal {
// Method from Object class (unchanged)
@Override
public String toString() {
return "This is an animal.";
}
// Method that we can change/override
public void makeSound() {
System.out.println("Animal makes a sound");
}
}
class Dog extends Animal {
// Overriding the makeSound method
@Override
public void makeSound() {
System.out.println("Woof!");
}
}
public class Main {
public static void main(String[] args) {
Animal animal = new Animal();
Dog dog = new Dog();
// Calling the unchanged toString() method from Object
System.out.println(animal.toString()); // Outputs: This is an animal.
System.out.println(dog.toString()); // Outputs: This is an animal. (inherited from Animal)
// Calling the changed makeSound() method
animal.makeSound(); // Outputs: Animal makes a sound
dog.makeSound(); // Outputs: Woof!
}
}