OOP AND ENCAPSULATION

Constructor Chaining and super()

Rule: If a constructor does not explicitly call super() or this(), the compiler inserts super() only if the superclass has a no-arg constructor.

class Ancestor {
    Ancestor(String msg) {
        System.out.println("Ancestor: " + msg);
    }
    // No no-arg constructor available!
}

class Parent extends Ancestor {
    // ❌ This would cause compile error:
    // Parent() {} // Implicit super() call fails
    
    // ✅ Must explicitly call super with argument:
    Parent() {
        super("Default parent message"); // Explicit call required
    }
    
    Parent(String name) {
        super("Parent: " + name);       // Explicit call required
    }
}

class Child extends Parent {
    Child() {
        // ✅ Implicit super() works - Parent has no-arg constructor
        System.out.println("Child constructor");
    }
}

Constructor execution order:

Child child = new Child();
// Output:
// Ancestor: Default parent message
// Child constructor

💡 Learning Tip: “No free lunch” - if parent needs arguments, children must provide them explicitly.