- Can a data field be declared abstract?
- Why would you use an abstract class?
- Can an interface have a constructor?
- Can a subclass be abstract even if its superclass is concrete?
- What is the use of an abstract class if it doesn’t have any subclasses?
- Is it compulsory for the abstract class to have at least one method as an abstract?
- Can a constructor be abstract?
- Can abstract class have body?
- Can you call an abstract method?
- Can we override abstract class?
- Can we inherit abstract class?
- Why can’t a constructor be final?
Can a data field be declared abstract?
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..
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.
Can an interface have a constructor?
No, you cannot have a constructor within an interface in Java. You can have only public, static, final variables and, public, abstract, methods as of Java7.
Can a subclass be abstract even if its superclass is concrete?
A subclass can be abstract even if its superclass is concrete. For example, the Object class is concrete, but its subclasses, such as GeometricObject, may be abstract. A subclass can override a method from its superclass to define it abstract. … In this case, the subclass must be defined abstract.
What is the use of an abstract class if it doesn’t have any subclasses?
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.
Is it compulsory for the abstract class to have at least one method as an abstract?
A class which contains 0 or more abstract methods is known as abstract class. If it contains at least one abstract method, it must be declared abstract. And yes, you can declare abstract class without defining an abstract method in it.
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 body?
Abstract methods cannot have body. Abstract class can have static fields and static method, like other classes. An abstract class cannot be declared as final. Only abstract class can have abstract methods.
Can you call an abstract method?
An abstract method is a method without a body. So you can’t just call an abstract method of an abstract class (you cannot instantiate an abstract class directly). … Alternatively you can remove the abstract keyword from the methods in your game class but still @Override them in your subclass.
Can we override abstract class?
An abstract method has no implementation. … Subclasses of an abstract class must implement (override) all abstract methods of its abstract superclass. The non-abstract methods of the superclass are just inherited as they are. They can also be overridden, if needed.
Can we inherit abstract class?
An abstract class defines the identity of a class. An interface can inherit multiple interfaces but cannot inherit a class. An abstract class can inherit a class and multiple interfaces. … An abstract class can declare constructors and destructors.
Why can’t a constructor be final?
The child class inherits all the members of the superclass except the constructors. In other words, constructors cannot be inherited in Java therefore you cannot override constructors. So, writing final before constructors makes no sense. Therefore, java does not allow final keyword before a constructor.