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I have a very basic question about abstract class in java.

As we know that we can't create an instance of an abstract class, then how JVM handles the instantiation of abstract class in java .

we can define a parameterized constrcutor in the abstract class and we can define another which extends the abstract class. In this situation who creates the instance of abstract class and invokes the constructor of the abstract class.

I want to understand, How JVM manages the object creation of abstract classes.

JAVA Beginner
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Sambit
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  • possible duplicate of [Interview : Can we instantiate abstract class?](http://stackoverflow.com/questions/13670991/interview-can-we-instantiate-abstract-class) – Elliott Frisch Dec 24 '13 at 07:30

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JVM cannot instantiate an abstract class it can instantiate only an instance of a non-abstract subclass of abstract class. Creating an instance means allocating space in memory necessary to hold all non-static fields and then initialing these fields by calling constructors.

Evgeniy Dorofeev
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  • I need a better answer if you could please explain from the view point of JVM internals. How JVM handles if the abstract class has constructor, how constructor gets invoked by JVM. – Sambit Dec 24 '13 at 11:11
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JVM can not instantiate Interface or Abstract classes.

Take a look at this .

In the JVM, every object has a pointer to its class, but only to its concrete class and not to its interface or abstract class. If we get the memory address of an object, we can get the address of its class easily. This method is useful only for classes whose instances can be created. Neither interfaces nor abstract classes can be used in this way.

Refer this for more details .

In the case of Abstract class and it's concrete SubClass, when you do like this:

AbstractClass obj = new ConcreteClass();

new operator creates an object of ConcreteClass, and invokes its constructor to initialize the state of the created object. In this process, the constructor of the abstract class is also called from the ConcreteClass constructor, to initialize the state of the object in the abstract class.

So, basically the object of AbstractClass is not created. It's just that it's constructor is invoked to initialize the state of the object.

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Sujith PS
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  • If the abstract class has a parameterized constructor and subclass extends the abstract class, how is constructor of abstract invoked ? – Sambit Dec 24 '13 at 11:09
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if Abstract class object is not created internally by the JVM, but only its constructor is invoked to initialise the state. Then without instantiation what is the point in initialisation and to which object initialisation is performed.

Ravi Routhu
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  • Welcome to stack over flow, while we appreciate your answers this post is pretty old and your answer is pretty much the same as one of the existing ones. Focus your effort on answering new questions :) – secretformula May 20 '14 at 18:33