The <code>super</code> Keyword in Java

super refers to the immediate parent in the inheritance chain. You use it to (1) call a parent constructor, (2) call an overridden parent method, or (3) access a parent field that was shadowed.

Calling the parent constructor

public class Vehicle {
    protected final String brand;
    public Vehicle(String brand) { this.brand = brand; }
}

public class Car extends Vehicle {
    private final int doors;
    public Car(String brand, int doors) {
        super(brand);                // must be the first statement
        this.doors = doors;
    }
}

If you omit super(...), the compiler inserts super(). If the parent has no no-arg constructor, you must call super(...) explicitly.

Calling an overridden parent method

public class Animal {
    public String speak() { return "generic sound"; }
}

public class Dog extends Animal {
    @Override
    public String speak() {
        return super.speak() + " (actually a bark)";
    }
}

Accessing a shadowed field

public class Parent { protected int x = 1; }
public class Child extends Parent {
    protected int x = 2;
    public void show() {
        System.out.println(x);          // 2 — child's field
        System.out.println(super.x);    // 1 — parent's
    }
}

Shadowing fields is generally a bad idea — it creates confusion. Prefer different names.

super in interfaces (Java 8+)

public interface Greeter { default String hi() { return "hi"; } }
public interface LoudGreeter { default String hi() { return "HI!"; } }

public class Both implements Greeter, LoudGreeter {
    @Override
    public String hi() {
        return Greeter.super.hi() + " / " + LoudGreeter.super.hi();
    }
}

Common mistakes

• Using super() with this() — you can have at most one, and it must be first.
• Skipping the parent constructor — if it has required parameters, the compiler won't let you.
• Shadowing fields by accident — a subclass field with the same name hides the parent's. Rename instead.

Related

Pillar: Java keywords. See also this, inheritance, constructors.