Why you use constructor chaining?

Answer 1

Constructor Chaining

We know that constructors are invoked at runtime when you say new on some class type as follows:

Lamborghini h = new Lamborghini();

But what really happens when you say new Lamborghini() ? (Assume Lamborghini extends Car and Car extends Object.)

1. Lamborghini constructor is invoked. Every constructor invokes the constructor of its superclass with an (implicit) call to super(),

2. Car constructor is invoked (Car is the superclass of Lamborghini).

3. Object constructor is invoked (Object is the ultimate superclass of all classes, so class Car extends Object even though you don't actually type "extends Object" into the Car class declaration. It's implicit.) At this point we're on the top of the hierarchy.

4. Object instance variables are given their explicit values. By explicit values, we mean values that are assigned at the time the variables are declared, like "int x = 27", where "27" is the explicit value (as opposed to the default value) of the instance variable.

5. Object constructor completes.

6. Car instance variables are given their explicit values (if any).

7. Car constructor completes.

8. Lamborghini instance variables are given their explicit values (if any).

9. Lamborghini constructor completes.