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Is it true that Abstract class objects never have to be instantiated?
Yes. An Abstract class cannot be instantiated.
What is abstrac class?
An abstract class is one that is not meant to be instantiated directly; it can only be subclassed.
What is the keyword used to declare a class which cannot be instantiated?
abstract all lower case.
When an abstract modifier applied to a class?
An Abstract class is a special kind of class that cannot be instantiated. It has one or more methods which are not implemented in the class. These methods are declared abstract and they do not contain any code inside them. Ex: abstract class Parent { public abstract String getSon(); public abstract String getDaughter(); .... .... //More methods that contain specific behaviour/code in them } The above is an abstract class "Parent" that has a lot of functionality but it has declared two abstract methods which have no code inside them. Any class that has one or more abstract methods has to be abstract. This abstract class cannot be instantiated. i.e., the below piece of code will not work. The code will not even compile. Parent object = new Parent();
Create an instance to an abstract class?
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"
When do you say an exception is handled?
There is no catch block that names either the class of exception that has been thrown or a class of exception that is a parent class of the one that has been thrown, then the exception is considered to be unhandled, in such condition the execution leaves the method directly as if no try has been executed
Difference between abstract and final class?
Abstract class is built to promote inheritance whereas a final class is built to avoid inheritanceAn Abstract class can be extended by another class whereas a final class cannot be extended
How do you call an abstract class from main method?
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.
What happens if an abstract modifier is applied to class. Explain?
The classes which have one or more abstract methods are abstract. To declare a class as abstract, use the abstract keyword in front of the class keyword, before the class declaration. Abstract classes cannot be instantiated. Similarly the new keyword cannot be used to create an object of the abstract class. Remember that the constructors and static variables cannot be declared as abstract. Any subclass of an abstract class must either implement all of the abstract methods in the superclass or be itself declared abstract.
What is abstract base class?
An abstract class is a class that cannot be directly instantiated. The purpose of such a class is to put some logic in a base class and force derived classes to implement the remaining functionality. Since the full functionality is only available in the derived class, the base class is declared as abstract so that it cannot be instantiated directly.
Why can't declare construtor as a static final abstract?
Because of the following reasons:static - If a constructor is static, an object instance cannot invoke it to initialize itself (Because static members are not linked to an object)abstract - because an abstract class cannot be instantiated and hence it will not have a constructor. If you make a concrete class's constructor abstract - it cannot be instantiated. eitherways it makes no sensefinal - a constructor cannot be final (thats the way java is designed)
Why you are not allowed to put an abstract method into a normal class?
You can't put an abstract method (pure-virtual method) in a normal class because the normal class would become abstract itself. Only non-abstract classes can be physically instantiated as objects, and only if they fully implement all the abstract methods inherited from their base classes.
