keywords-super.md

super

When implementing inheritance, it's sometimes useful for a child class to call its parent's methods. With the super keyword, we can do just that.

You can use super to do anything the parent could. You can use this in any method or function on a child class.

In Constructors

In Java, if a you extend a class without a zero-argument constructor, you'll need to use one of the parent's constructors before making your object. For example:

public class Person {
    // We'll let whoever makes a 'person' specify a name
    private String name;
    
    public Person (String name) {
        this.name = name;
    }
}


public class Student extends Person {
    // We don't need to specify a name.
    // Person defines it for us!
    private School school;
    
    public Student(String name, School school) {
        // Note how we don't need a matching constructor, we just have to make our parent class happy
        super(name);
        this.school = school;
    }
}

Overriding

super is especially useful when overriding methods to extend behavior. For example:

public class Person {
    private String name;
    
    public Person (String name) {
        this.name = name;
    }
    
    public void morningRoutine() {
        // Wake up
        // Eat breakfast
    }
}


public class Student extends Person {
    private School school;
    
    public Student(String name, School school) {
        super(name);
        this.school = school;
    }
    
    // This next annotation reminds us that we're changing what our parent class does.
    @Override
    public void morningRoutine() {
        // hit snooze
        
        // If we left this out, we'd never wake up!
        super.morningRoutine();
        // make sure bag is packed
        // go to school
    }
}