Unit 9.4 Inheritance - Teacher notebook • 6 min read

9.4 Super Keyword

Using the super keyword to call a superclass’s method.

public class Performer { //superclass
    public void practice(){
        System.out.println("Honing my craft!");
    }
    public void perform(){
        System.out.println("Performing for an audience!");
    }
}

public class Dancer extends Performer { //subclass
    public void perform(){
        System.out.println("Dancing on the stage!");
    }
}

public class BalletDancer extends Dancer { //subclass
    public void jete(){
        System.out.println("Leaping...");
    }
    public void pirouette(){
        System.out.println("Spinning...");
    }
    public void perform(){
        jete();
        pirouette();
    }
        public static void main(String[] args){
            BalletDancer derrick = new BalletDancer();
            derrick.practice();
            derrick.perform();
        }
}

System.out.println("BalletDancer class: ");
BalletDancer.main(null);

BalletDancer class: 
Honing my craft!
Leaping...
Spinning...

public class Performer { //superclass of Dancer class
    public void practice(){
        System.out.println("Honing my craft!");
    }
    public void perform(){
        System.out.println("Performing for an audience!");
    }
}

public class Dancer extends Performer { //superclass of BalletDancer class
    public void perform(){
        System.out.println("Dancing on the stage!");
    }
}

public class BalletDancer extends Dancer {
    public void jete(){
        System.out.println("Leaping...");
    }
    public void pirouette(){
        System.out.println("Spinning...");
    }
    public void perform(){ 
        perform();//Why is this wrong?
        jete();
        pirouette();
    }
        public static void main(String[] args){
            BalletDancer derrick = new BalletDancer();
            derrick.practice();
            derrick.perform();
        }
}

System.out.println("BalletDancer class: ");
BalletDancer.main(null);

Note:

Super keyword can be placed in any order as it prints out chronologically.

    public void perform(){ 
        super.perform();
        jete();
        pirouette();
    }

will print out…

Honing my craft!
Dancing on the stage!
Leaping...
Spinning...

However, if we were to write:

    public void perform(){ 
        jete();
        pirouette();
        super.perform();
    }

It will print out…

Honing my craft!
Leaping...
Spinning...
Dancing on the stage!

What if we use 2 super keywords?

public class Performer { //superclass
    public void practice(){
        System.out.println("Honing my craft!");
    }
    public void perform(){
        System.out.println("Performing for an audience!");
    }
}

public class Dancer extends Performer { //subclass
    public void perform(){
        super.perform();
        System.out.println("Dancing on the stage!");
    }
}

public class BalletDancer extends Dancer { //subclass
    public void jete(){
        System.out.println("Leaping...");
    }
    public void pirouette(){
        System.out.println("Spinning...");
    }
    public void perform(){
        super.perform();
        jete();
        pirouette();
    }
        public static void main(String[] args){
            BalletDancer derrick = new BalletDancer();
            derrick.practice();
            derrick.perform();
        }
}

System.out.println("BalletDancer class: ");
BalletDancer.main(null);

BalletDancer class: 
Honing my craft!
Performing for an audience!
Dancing on the stage!
Leaping...
Spinning...

Popcorn Hack

Create a subclass and a superclass by calling the methods from the superclass from the subclass using the keyword super.