- Is it mandatory to have abstract method in abstract class?
- Can we inherit abstract class?
- When should we use abstract class?
- Is it possible to inherit from multiple abstract classes in Java?
- Can abstract class have static and final methods?
- Can we declare abstract class as static?
- Can constructor be private?
- What is difference between abstract class and interface?
- Can abstract class have constructor C++?
- Why can’t we instantiate an abstract class?
- Can abstract method have body?
- Can abstract class have method definition?
- Can an abstract class be private?
- Can we declare abstract class as final?
- Can abstract class have constructor?
Is it mandatory to have abstract method in abstract class?
It’s not necessary for an abstract class to have abstract method.
We can mark a class as abstract even if it doesn’t declare any abstract methods.
If abstract class doesn’t have any method implementation, its better to use interface because java doesn’t support multiple class inheritance..
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.
When should we use abstract class?
When to use an abstract classAn abstract class is a good choice if we are using the inheritance concept since it provides a common base class implementation to derived classes.An abstract class is also good if we want to declare non-public members. … If we want to add new methods in the future, then an abstract class is a better choice.More items…•
Is it possible to inherit from multiple abstract classes in Java?
A: Because Java doesn’t support multiple inheritance. … A: Java has a rule that a class can extend only one abstract class, but can implement multiple interfaces (fully abstract classes).
Can abstract class have static and final methods?
Yes, it can. But the final method cannot be abstract itself (other non-final methods in the same class can be).
Can we declare abstract class as static?
Yes, of course you can define the static method in abstract class. you can call that static method by using abstract class,or by using child class who extends the abstract class. Also you can able to call static method through child class instance/object.
Can constructor be private?
Yes, we can declare a constructor as private. If we declare a constructor as private we are not able to create an object of a class. We can use this private constructor in the Singleton Design Pattern.
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 abstract class have constructor C++?
An abstract class can have constructor similar to normal class implementation. In the case of the destructor, we can declare a pure virtual destructor. It is important to have a destructor to delete the memory allocated for the class.
Why can’t we instantiate an abstract class?
Because an abstract class is an incomplete class (incomplete in the sense it contains abstract methods without body and output) we cannot create an instance or object; the same way you say for an interface. You CAN instantiate an abstract class. You only need to provide a concrete subclass.
Can abstract method have body?
Abstract methods are declaration only and it will not have implementation. It will not have a method body. A Java class containing an abstract class must be declared as abstract class. An abstract method can only set a visibility modifier, one of public or protected.
Can abstract class have method definition?
Abstract classes are similar to interfaces. You cannot instantiate them, and they may contain a mix of methods declared with or without an implementation. However, with abstract classes, you can declare fields that are not static and final, and define public, protected, and private concrete methods.
Can an abstract class be private?
If a method of a class is private, you cannot access it outside the current class, not even from the child classes of it. But, incase of an abstract method, you cannot use it from the same class, you need to override it from subclass and use. Therefore, the abstract method cannot be private.
Can we declare abstract class as final?
In short, an abstract class cannot be final in Java, using both abstract and final modifier with a class is illegal in Java. … An abstract method must be overridden to be useful and called but when you make the abstract method final it cannot be overridden in Java, hence there would be no way to use that method.
Can abstract class have 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.