this vs super Keyword in Java

Expected Interview Answer

Step-by-Step Explanation

1. Step 1

   Use this for current members

   Reference the current object's fields and methods, e.g. this.name or this.calculate().

2. Step 2

   Disambiguate names

   When a parameter shadows a field, use this.field = field to assign correctly.

3. Step 3

   Chain constructors with this()

   Call another constructor of the same class as the first statement using this(args).

4. Step 4

   Use super for parent members

   Access an overridden method or hidden field of the parent with super.method().

5. Step 5

   Call the parent constructor

   Invoke the parent's constructor with super(args) as the first statement in a subclass constructor.

Code Example

class Animal {
    String name;
    Animal(String name) {
        this.name = name;          // this resolves the shadowed field
    }
    void speak() {
        System.out.println(name + " makes a sound");
    }
}

class Dog extends Animal {
    Dog(String name) {
        super(name);               // call parent constructor
    }
    @Override
    void speak() {
        super.speak();             // reuse parent behaviour
        System.out.println(this.name + " barks");
    }
}

public class Main {
    public static void main(String[] args) {
        new Dog("Rex").speak();
    }
}

Follow-up Questions

• Why must this() or super() be the first statement in a constructor?
• Can you use both this() and super() in one constructor?
• How does this help when a parameter shadows a field?
• When would you call super.method() from an override?
• What happens if you don't explicitly call super() in a subclass constructor?