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Answered 2012-05-20 11:50:02

No. The whole point of an abstract class is that it can not be instantiated.

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No. You must create a subclass of the abstract class in order to be able to instantiate it.

Because, the Abstract class is not a complete class and does not have implementation for a few methods. As a result you cannot instantiate them

An abstract class cannot have a constructor and hence you cannot invoke the constructor of the class - i.e., you can instantiate an abstract class and hence you cannot call the constructor of an abstract class.

An abstract class(or classes) can't have a constructor and hence you cannot invoke the constructor of the class (for example, you can instantiate an abstract class and hence you cannot call the constructor of an abstract class).

No. The whole idea of an abstract class is that you can't instantiate it directly. You need to create subclasses first.

No. An abstract class is an incomplete class. It does not have all functionality and features implemented in it. So, you cannot instantiate it. If you try to call the constructor for an abstract class, you will get a compilation error

Abstract classes are classes that can't be instantiated directly. In other words, you are meant to create subclasses, which you instantiate.

You cannot create an instance of an abstract class. For ex: Public abstract AbsTest { … } AbsTest ex = new AbsTest(); Lets say we have a class declaration AbsTest that is abstract and then I try to instantiate it, the compiler will give me an error stating that "An Abstract class cannot be instantiated"

By using the abstract keyword in the class declaration line. Ex: public abstract ClassName {} The Java compiler will force you to use the abstract keyword in the class declaration line if one or more methods in your class are abstract (no implementation) or if you have not provided implementations for one or more methods of an interface that you are implementing in your class definition. You cannot instantiate an abstract class.

No. You cannot instantiate an interface. However, you can implement the interface using a class and instantiate the class

Because that's the whole idea of declaring a class abstract - to avoid objects from being instantiated. The general idea is that an abstract class is "incomplete" - some details have to be filled out in derived (inherited) classes.

In C++, an abstract data type is a class that must be derived into a child class. It is not possible to instantiate an abstract class. Another way to define this is to say that an abstract class contains pure virtual functions or that it inherits from a class with pure virtual functions but does not provide an implementation for them.

A more prcise description of difference is as follows.... an interface is a specification of a set of methods that the implementation class must adhere to, while an abstract class is indeed an implementation class albeit a class that is not concrete, i.e., one cannot directly instantiate an abstract class.

It is an abstract class so you can't instantiate it directly, but have to use a subclass instead.

No. The abstract keyword means that you cannot instantiate the class unless you extend it with a subclass. The final keyword means that you cannot create subclasses of that class.Combining them would lead to an unusable class, so the compiler will not let this happen.

An Abstract class is similar to an interface. You cannot instantiate them, but you can extend them. Any class that extends the abstract class has to provide the implementation to the abstract methods. Hence these classes can be used as a skeleton to similar classes where some common functionality may be required. Such functionality can also be embedded into these classes. Unlike interfaces, abstract classes can have method code also. So they are very useful.

abstract class in java is mainly designed for giving abstract method i.e declarations alone, Instantiation is a process by which jvm allocates memory for that. But only with the method declaration jvm will not know how much memory should give for the abstract method. So abstract classes are no need to instantiate before the method implementation, The concrete class which extends the abstract class, will provide method implementation at that time only abstract class constructor will run

You cannot instantiate an object of an abstract class. Example: You might have two objects 'man' and 'woman' which inherit common characteristics (two eyes, a nose etc) from 'human'. You wouldn't want humans that are neither walking around so you make human an abstract class as you'll never need a human object.

We can't instantiate both interfaces and abstract classes.The only one difference between them is that an interface can't contain concrete(fully defined) methods where as an abstract class may contain them.An abstract class not necessarily contain abstract methods. we can make a class as abstract class even it does not has any abstract methods.When there is a need to write both abstract and concrete methods in a single unit we have to use an abstract class instead of an interface since an interface cant contain concrete methods.All the fields(or properties) of an interface are by default 'static final' even when you don't mention explicitly. And all methods are 'public abstract'.But in an abstract class we can have any type of fields and methods.

abstract class is a class label with abstract. It is just like a common class, with the following characterics: 1. Abstract class cannot be instantiate with an instance. 2. Abstract class may have abstract methods, while the normal class cannot have abstract methods. a virtual function in C# is a way to provide a default implementation for the class hierarchy. Both abstract class and common class (not sealed) can have virtual methods/ functions. Note that an abstract method (of an abstract class) is defining the intent, no codes (no default behavior), the implementation are left for the derived classes to do so. The virtual function if defined in an abstract class must define the implementation, the minimum is to do nothing: public abstract class Vehicle { public abstract int GetNumberOfTires(); public virtual void Move() { // default is doing nothing} } public class Car : Vehicle { public override int GetNumberOfTires() { return 4; } public override void Move() { throws new OutOfFuelExpection(); } }

Abstract classes are those classes that cannot be instantiated. Those classes are not fully implemented. Abstract class is base class for the family of child classes. It may contain some basic features but for some features only signature are given, the body of those methods must be written after inheriting this abstract class. Only if child implements all of the abstract methods it might be used (instantiated), otherwise child class is abstract too. To summarize it, you cannot instantiate class that is partial (missing all/some implementation).

Abstract classes are to be extended until to a concrete class.Can have both abstract & non abstract methods.An Abstract class can not be instantiated.A non abstract class can be extended to an abstract class.If At least one abstract method present in a class then that class must be abstract.abstract & final modifiers can never be together.abstract classes can have both abstract methods & non abstract methods.

Yes an abstract class can inherit from another abstract class but all the methods of the base abstract class must be abstract.

In two situations:You want the child class to provide certain behavior while making sure that certain other behavior is as you want it (Through the concrete methods that you create)You dont want any other class to be able to instantiate your class

The concept of abstraction is concept talked about when talking about inheritance. When you make a class abstract, it means that the class is a general "abstract" idea, not something you want to instantiate (create an object from.) However, abstract classes are useful for when you want to create real sub-classes of the abstract class. For example, you could have an abstract class named "animal" that had the general characteristics of all animals, then you can have regular sub-classes that inherit "animal", like "dog", "cat" or "horse." The reason for making the "animal" class abstract is to make sure that one can't create a generic "animal" object, but so they can create objects that inherit the idea of "animal."

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