A class which is declared as abstract is known as an abstract class. It can have abstract and non-abstract methods. It needs to be extended and its method implemented. It cannot be instantiated.
Are abstract classes implemented?
Abstract classes cannot be instantiated, but they can be subclassed. When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class.
Can all abstract classes be extended?
An abstract class can extend another abstract class. And any concrete subclasses must ensure that all abstract methods are implemented.
Can we extend abstract class in Java?
In Java, abstract means that the class can still be extended by other classes but that it can never be instantiated (turned into an object).
Do all abstract methods have to be implemented?
An abstract method doesn’t have any implementation (method body). A class containing abstract methods should also be abstract. We cannot create objects of an abstract class. To implement features of an abstract class, we inherit subclasses from it and create objects of the subclass.
Can abstract class extend interface?
Multiple implementations: An interface can extend another Java interface only, an abstract class can extend another Java class and implement multiple Java interfaces.
How do you extend two abstract classes?
If you extend an abstract class, you must either make the child class abstract or it must fulfill the contract of the parent class. As a design observation, I would suggest that you try to make oneMethod() either final or abstract.
Can abstract class extends concrete class?
An abstract class can not extend a concrete class.
References:
- https://docs.oracle.com/javase/tutorial/java/IandI/abstract.html
- https://cloudacademy.com/course/object-oriented-development/interfaces-and-abstract-classes/
- https://idratherbewriting.com/java-abstract-methods/
- https://www.programiz.com/java-programming/abstract-classes-methods
- https://www.geeksforgeeks.org/difference-between-abstract-class-and-interface-in-java/
- https://stackoverflow.com/questions/18360873/extending-an-abstract-class-implementing-abstract-methods
- https://coderanch.com/t/244240/certification/abstract-class-extend-concrete-class