CODEWITHSUNDEEP
javaclassconstructorabstract
user1942362
user1942362

Reputation: 143

java abstract class, Constructor not called in super-class, Why?

Below is a simple example. I have two abstract classes, A and B, one concrete class, C, which includes the abstract method.

When I create a new C, I expected to see the constructors of A and B being called. Any idea why they are not called?

//Q.java
class Q {
    abstract class A {
        A() {
            System.out.println("in A");
        }
        public abstract void sayHi();
    }
    abstract class B extends A {
        B() {
            super();
            System.out.println("in B");
        }
    }
    class C {
        C() {
            super();
            System.out.println("in C");
        }
        public void sayHi() {
            System.out.println("Hi!");
        }
    }

    Q() {
        C Ccc = new C();
    }

    public static void main(String[] args) {
        Q z = new Q();
    }
}

Upvotes: 0

Views: 2649

Answers (6)

Rahul
Rahul

Reputation: 16335

C and B are not related in any way. super class of C is java.lang.Object by default

C should extend B like 

class C extends B{ .. }

In such a case, it will call the super class constructors.

Also, you do not need to call super() explicitly as it is implicitly there.

Upvotes: 1

deepak
deepak

Reputation: 1378

See, we have the super class Object which all classes extend implicitly. so if we have public class A{} then it is equivalent to writing public class A extends Object{} . But if you want to extend another class of your own then you have to explicitly mention it as public class B extends A{} else java will treat Object as your super class. (NOTE: even it this case Object is a super class to 'B' but this is because it is a super class to 'A' and hence 'B'). So if you don't explicitly mention the 'B extends A' then class B will have Object as its only super class. More over you dont need mention super() in the sub class constructor. This too is called implicitly.

Upvotes: 2

lol
lol

Reputation: 3390

Just make:

class c extends b{

It will work now.. you have not extended b in c..

Upvotes: 2

Azodious
Azodious

Reputation: 13872

you should extends the abstract classes from class c.

class c extends b {

Without extending b explicitely, it is equivalent to

class c extends Object {

and, hence call to super invokes Object constructor.

Upvotes: 2

Woot4Moo
Woot4Moo

Reputation: 24316

Because the super class of c is Object

Further class names start with upper case letters A,B,C,etc

If you want to see both a and b invoked do this: 

class c extends b

Upvotes: 6

xlecoustillier
xlecoustillier

Reputation: 16351

Your class c doesn't extend class b or a, so it can't call their constructors using super() and calls Object constructor instead.

Try this :

class c extends b {
    public c(){
        super();
        //...
    }
}

Upvotes: 3

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