What is a Constructor in Java? In Java, a constructor is a special type of method that is used to initialize objects. When you create an object of a class, the constructor is called automatically. Its main job is to set the initial values of the object’s properties or perform any setup that the object needs before it can be used. Why Do We Need Constructors? You need constructors because: Initialization : Constructors are responsible for initializing an object when it is created. Automatic Execution : A constructor is automatically called when an object is created, so you don’t have to manually initialize every property. Simplifying Object Creation : It simplifies object creation by providing default values or custom initialization. Where Do Constructors Fit in Java? Constructors fit within a class. They are used whenever a new object of that class is created, and they allow the object to be initialized. Constructors must have the same name as the class, and they don't have a re...
In Java, when dealing with multilevel inheritance and constructors, the `super` keyword plays a crucial role. The `super` keyword is used to call the constructor of the immediate superclass from within the subclass constructor. This is essential for initializing the inherited members of the superclass before initializing the members of the subclass.
Let's illustrate how `super` keyword is used to handle multilevel constructors:
class Animal {
String type;
Animal(String type) {
this.type = type;
System.out.println("Animal constructor called");
}
void eat() {
System.out.println("Animal is eating");
}
}
class Dog extends Animal {
String breed;
Dog(String type, String breed) {
super(type); // Calling superclass constructor
this.breed = breed;
System.out.println("Dog constructor called");
}
void bark() {
System.out.println("Dog is barking");
}
}
class Labrador extends Dog {
String color;
Labrador(String type, String breed, String color) {
super(type, breed); // Calling superclass constructor
this.color = color;
System.out.println("Labrador constructor called");
}
void playFetch() {
System.out.println("Labrador is playing fetch");
}
}
public class Main {
public static void main(String[] args) {
Labrador labrador = new Labrador("Canine", "Golden Retriever", "Golden");
labrador.eat(); // Inherited method from Animal
labrador.bark(); // Inherited method from Dog
labrador.playFetch(); // Specific to Labrador
}
}
In this example:
- The `Animal` class has a constructor that initializes the `type` of animal.
- The `Dog` class extends `Animal` and has its own constructor that initializes the `breed` of dog.
- The `Labrador` class extends `Dog` and has its own constructor that initializes the `color` of the Labrador.
- Each subclass constructor uses `super()` to call the constructor of its immediate superclass.
- This ensures that the constructors of all classes in the hierarchy are invoked properly, initializing the state of each object.
By using the `super` keyword, we ensure that constructors are called in the correct order in the multilevel inheritance hierarchy, allowing for proper initialization of inherited members and avoiding inconsistencies in object state.
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