Mell Is it possible to declare a class as both abstract and final?
If you declare a class abstract, to use it, you must extend it and if you declare a class final you cannot extend it, since both contradict with each other you cannot declare a class both abstract and final if you do so a compile time error will be generated.
Can a final class be abstract?
Hence, a final class cannot contain abstract methods whereas an abstract class can contain a final method. Below is an example which demonstrates the combination of abstract and final classes. Clearly, this implementation is invalid because a final class cannot have an abstract method.
Can an abstract class define both?
Yes—an abstract parent can have both abstract and non-abstract children. Can an abstract method be defined in a non-abstract class? A. No—if a class defines an abstract method the class itself must be abstract.
Can a class be both static and abstract?
An abstract can contain a static method. It is because a static method though not overridden can be hidden. But an abstract method cannot be declared static at the same time as an abstract method must be overridden ans implemented by a subclass’s method and declaring it static will prevent overriding.
Can an abstract class have a constructor?
Yes, an Abstract class always has a constructor. If you do not define your own constructor, the compiler will give a default constructor to the Abstract class.
Can a constructor be final?
No, a constructor can’t be made final. A final method cannot be overridden by any subclasses. But, in inheritance sub class inherits the members of a super class except constructors. In other words, constructors cannot be inherited in Java therefore, there is no need to write final before constructors.
Can an abstract class be private?
Abstract classes can have private methods. Interfaces can’t. Abstract classes can have instance variables (these are inherited by child classes).
Can a constructor be abstract?
You can’t have an abstract constructor, as abstract means you need to provide the implementation for that at some point of time in your subclass. But you cannot override constructor. There will be no point in having an abstract constructor : Since the constructor needs to be of the same name as of class.
Can abstract class have constructors?
The constructor inside the abstract class can only be called during constructor chaining i.e. when we create an instance of sub-classes. This is also one of the reasons abstract class can have a constructor.
Why can’t an abstract method be static?
An abstract class cannot have a static method because abstraction is done to achieve DYNAMIC BINDING while static methods are statically binded to their functionality. A static method means behavior not dependent on an instance variable, so no instance/object is required.
Can a final class have an abstract method?
NOTE :- A final class can not have abstract methods and an abstract class can not be declared final. Compilation error will occur as – The class can be either abstract or final, not both.
Can a subclass be overridden by an abstract class?
The answer is No. Because if a class is defined final it cannot be overridden .But if you create an abstract class then it should be overridden by the subclass . Hence an abstract class cannot be final.
Can a final class be subclassed or declared?
A final class is considered complete and can not be subclassed (It’s methods can not be overridden ). In case of abstract class, we have to proved implementation to abstract methods in subclasses.
What is the purpose of an abstract class?
The main purpose of an Abstract class is overriding of its abstract methods by the Child/Derived class which is inheriting from the Abstract class. That is how we achieve (partial) abstraction.