How many objects are created due to inheritance in java?

How many objects are created due to inheritance in java?

Great question. What you are probing is how Java initializes objects – and there are a number of steps involved.

i know is constructor is also a method (Maybe i am wrong).

Nearly right. The Constructor is a special method. If you decompile a class file, youll see the constructors get renamed to <init>. <init> is treated differently from other methods and, for example, cant be called explicitly except through use of the keyword new or super. This is so fundamental that it is implemented in the JVM itself rather than being something defined in the Java language.

How many number of Object is created in this case.

One object is created – an instance of C.

C is additionally and simultaneously an instance of B and an instance of A and also Object.

If one object is created then how internally super() is calling Parent class Constructor . How Super is able to call parent class constructor.

This is where we get into initialization – initialization is how the JVM creates a new instance of an object and sets all the member values – those of the specific class and those of the superclasses. There are several stages involved:

  • Load all the referenced classes and initialize those classes. Class initialization is itself non-trivial so I wont cover it here. It is well worth reading up.
  • Allocate a chunk of memory for holding the members of the instance, which will include the all members of A, B and C. NOTE this explains one aspect of your question: how can the constructors of the base class and its subclasses update or refer to the same object – all the members of the instance from all classes are stored one after the other in the same chunk of memory.
  • Initialize all the members to their default value. For example, int and float members will be set to 0 and 0.0f.
  • Execute or calculate the member initializers, eg:

    private int a = 10;
    private int b = a * 5;
    private String c = Singleton.getInstance().getValue();
    
  • Note (1) that member initialization occurs strictly in the order that members are declared in the class. This means that references to members later in the declaration are broken:

    private int a = b * 5; // Forward reference; wont compile
    private int b = 10;
    
  • Note (2) that there is a under-used facility in Java to run arbitrary code to initialize values before the constructor is executed. These code blocks are executed at this time again strictly in order of declaration:

    private int a;
    private int b = 1;
    {
        // Initization occurs after b but before c.
        // c cannot be referenced here at all
        int i = SomeClass.getSomeStatic();
        a = i * 2;
    }
    private int c = 99;
    
  • Execute the constructor of C. Constructors must either directly invoke a constructor from the superclass or the compiler will automatically add super() as the first line of the constructor. This means that the constructors are strictly executed in order:

    1. Object
    2. A
    3. B
    4. C

The object is now initialized and is ready for use. You can do some dangerous stuff if you initialize value using instance methods:

public class Wrong {
    int a = getB(); // Dont do this!
    int b = 10;
    public int getB() {
         return b;
    }
}

Here, a is initialized to 0. This is because, at the point getB() is invoked, Java has cleared the value of b to the default (0), but has not yet set it to 10 in the second phase of initialization.

In summary – there is only one object and it is created and initialized in a number in stages. During those stages, the object is, by definition, not completely defined.

  1. There will be one and only one object will be created and ie. A object.

  2. You can imagine like when class A extends B, then all methods and variables are copied to class A.

How many objects are created due to inheritance in java?

In Code only one object will be created and super call the parent class constructor .

Prove of object creation :

package one;

public class A {
    public static A super_var;

    public A() {
        super_var = this;
        System.out.println(Constrcutor of A invoked);
    }
}

package two;

public class B extends A {
    public static A sub_var;

    public B() {
        sub_var = this;
        System.out.println(Constructor of B invoked);
    }

    public void confirm() {
        if (sub_var == A.super_var)
            System.out.println(There is only one object is created);
        else
            System.out.println(There are more than one object created);
    }

    public static void main(String Args[]) {
        B x = new B();
        x.confirm();
    }
}

This will prove that there will be only one object created.

And about Super().
What I know that it call Parent class constructor . and each constructor ahve Super() as first statement like you mention in your code . so that you know

I dont know how it internally call super class constructor .

Hope this will make you understand there is only the instace you create in program

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