- What is abstract class in OOP?
- Why would you use an abstract class?
- What is difference between abstract class and interface?
- Can an abstract class have a constructor?
- How many interfaces can a class inherit?
- How many abstract classes can be used in multilevel inheritance?
- Can an abstract class extend concrete?
- Can we inherit abstract class in Interface?
- How do you declare an abstract class in Java?
- What is the purpose of abstract class in Java?
- Can we inherit abstract class?
- Can we inherit more than one abstract class?
What is abstract class in OOP?
Abstract classes and methods are when the parent class has a named method, but need its child class(es) to fill out the tasks.
An abstract class is a class that contains at least one abstract method.
An abstract method is a method that is declared, but not implemented in the code..
Why would you use an abstract class?
The short answer: An abstract class allows you to create functionality that subclasses can implement or override. An interface only allows you to define functionality, not implement it. And whereas a class can extend only one abstract class, it can take advantage of multiple interfaces.
What is difference between abstract class and interface?
Classes can implement multiple interfaces, but only one abstract class. Abstract classes can contain non-abstract methods. They can both have methods, variables, and neither one can be instantiated. All variables declared in an interface are final, while an abstract class may contain non-final variables.
Can an abstract class have a constructor?
Yes! Abstract classes can have constructors! Yes, when we define a class to be an Abstract Class it cannot be instantiated but that does not mean an Abstract class cannot have a constructor. Each abstract class must have a concrete subclass which will implement the abstract methods of that abstract class.
How many interfaces can a class inherit?
A class can implement more than one interface at a time. A class can extend only one class, but implement many interfaces. An interface can extend another interface, in a similar way as a class can extend another class.
How many abstract classes can be used in multilevel inheritance?
11. How many abstract classes can be used in multilevel inheritance? Explanation: At least one class must implement all the undefined functions. Hence there must be at least one class which is not abstract.
Can an abstract class extend concrete?
An abstract class always extends a concrete class ( java. lang. … If you want to instantiate it, you will have to subclass it with a concrete implementation of those abstract methods and instantiate it through the concrete class.
Can we inherit abstract class in Interface?
An interface can inherit multiple interfaces but cannot inherit a class. An abstract class can inherit a class and multiple interfaces. … An interface can have only public abstract methods. An abstract class has protected and public abstract methods.
How do you declare an abstract class in Java?
An abstract class is a class that is declared abstract —it may or may not include abstract methods. Abstract classes cannot be instantiated, but they can be subclassed.
What is the purpose of abstract class in Java?
Java Abstract class can implement interfaces without even providing the implementation of interface methods. Java Abstract class is used to provide common method implementation to all the subclasses or to provide default implementation. We can run abstract class in java like any other class if it has main() method.
Can we inherit abstract class?
Abstract Class But, if a class has at least one abstract method, then the class must be declared abstract. If a class is declared abstract, it cannot be instantiated. To use an abstract class, you have to inherit it from another class, provide implementations to the abstract methods in it.
Can we inherit more than one abstract class?
Basically, the rule says that you can inherit from (extend) as many classes as you want, but if you do, only one of those classes can contain concrete (implemented) methods. … A class can extend at most one abstract class, but may implement many interfaces. That is, Java supports a limited form of multiple inheritance.