When do I use super()?

Question

I'm currently learning about class inheritance in my Java course and I don't understand when to use the super() call?

Edit:
I found this example of code where super.variable is used:

class A {     int k = 10; }  class Test extends A {     public void m() {         System.out.println(super.k);     } } 

So I understand that here, you must use super to access the k variable in the super-class. However, in any other case, what does super(); do? On its own?

Answer 1

super is used to call the constructor, methods and properties of parent class.

Answer 2

Calling exactly super() is always redundant. It's explicitly doing what would be implicitly done otherwise. That's because if you omit a call to the super constructor, the no-argument super constructor will be invoked automatically anyway. Not to say that it's bad style; some people like being explicit.

However, where it becomes useful is when the super constructor takes arguments that you want to pass in from the subclass.

public class Animal {    private final String noise;    protected Animal(String noise) {       this.noise = noise;    }     public void makeNoise() {       System.out.println(noise);    } }  public class Pig extends Animal {     public Pig() {        super("Oink");     } }