What is the super Keyword in Java?

The super keyword refers to the immediate parent class object. It is used to access parent class methods, constructors, and variables when hidden by subclass.

1. Access Parent Class Variable

class Animal {
    String color = "White";
}

class Dog extends Animal {
    String color = "Black";
    
    void printColor() {
        System.out.println(color);        // Black (child)
        System.out.println(super.color);  // White (parent)
    }
    
    public static void main(String[] args) {
        Dog d = new Dog();
        d.printColor();
        // Output:
        // Black
        // White
    }
}

2. Invoke Parent Class Method

class Vehicle {
    void run() {
        System.out.println("Vehicle is running");
    }
}

class Bike extends Vehicle {
    @Override
    void run() {
        System.out.println("Bike is running safely");
    }
    
    void display() {
        run();        // Calls child method
        super.run();  // Calls parent method
    }
    
    public static void main(String[] args) {
        Bike b = new Bike();
        b.display();
        // Output:
        // Bike is running safely
        // Vehicle is running
    }
}

3. Invoke Parent Class Constructor

class Person {
    String name;
    int age;
    
    Person(String name, int age) {
        this.name = name;
        this.age = age;
        System.out.println("Person constructor called");
    }
}

class Student extends Person {
    int studentId;
    
    Student(String name, int age, int id) {
        super(name, age); // Must be first statement
        this.studentId = id;
        System.out.println("Student constructor called");
    }
    
    void display() {
        System.out.println("Name: " + name + ", Age: " + age + ", ID: " + studentId);
    }
    
    public static void main(String[] args) {
        Student s = new Student("Alice", 20, 101);
        s.display();
    }
}
// Output:
// Person constructor called
// Student constructor called
// Name: Alice, Age: 20, ID: 101

Important Rules

• super() must be the first statement in a constructor
• super cannot be used in static contexts
• Unlike this, super does not refer to current object but parent part

this vs super - Quick Comparison

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