Which of the following is correct an abstract class does not contain constructors
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True, A method-defined abstract must always be redefined in the subclass, thus making overriding compulsory or making the subclass itself abstract. Any class that contains one or more abstract methods must also be declared with an abstract keyword. There can be no object of an abstract class.
Show A class which has the abstract keyword in its declaration is called abstract class. Abstract classes should have zero or more abstract methods. i.e., methods without a body. It can have multiple concrete methods. Abstract classes allow you to create blueprints for concrete classes. But the inheriting class should implement the abstract method. Abstract classes cannot be instantiated. Important Reasons For Using Interfaces
Important Reasons For Using Abstract Class
What is Interface?The interface is a blueprint that can be used to implement a class. The interface does not contain any concrete methods (methods that have code). All the methods of an interface are abstract methods. An interface cannot be instantiated. However, classes that implement interfaces can be instantiated. Interfaces never contain instance variables but, they can contain public static final variables (i.e., constant class variables) Difference between Interface and Abstract Class in JavaAn abstract class permits you to make functionality that subclasses can implement or override whereas an interface only permits you to state functionality but not to implement it. A class can extend only one abstract class while a class can implement multiple interfaces. A Constructor is a special member function used to initialize the newly created object. It is automatically called when an object of a class is created. Why interfaces can not have the constructor?
Java
car is created Maruti is running0
car is created Maruti is running2 car is created Maruti is running3 car is created Maruti is running2 car is created Maruti is running5 car is created Maruti is running2 car is created Maruti is running7 car is created Maruti is running8
car is created Maruti is running9
car is created Maruti is running2 car is created Maruti is running3 car is created Maruti is running2 car is created Maruti is running5 car is created Maruti is running2 // interface can not have a constructor4
car is created Maruti is running2 // interface can not have a constructor9
car is created Maruti is running8
car is created Maruti is running8 car is created Maruti is running8 Output 15 In the above program, we have created an interface Subtraction which defines a method subtract(), whose implementation is provided by the class GFG. In order to call a method, we need to create an object, since the methods inside the interface by default public abstract which means the method inside the interface doesn’t have the body. Therefore, there is no need for calling the method in the interface. Since we cannot call the methods in the interface, there is no need for creating the object for interface and there is no need of having a constructor in it. Can an abstract class not have a constructor?It is used to initialize an object. 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 an abstract class contain a constructor?Like any other classes in Java, abstract classes can have constructors even when they are only called from their concrete subclasses.
Why object can not be created for an abstract class though it contains a constructor?Because it's abstract and an object is concrete. An abstract class is sort of like a template, or an empty/partially empty structure, you have to extend it and build on it before you can use it. abstract class has a protected constructor (by default) allowing derived types to initialize it.
Are the constructors in an abstract class protected?An abstract class by definition cannot be instantiated directly. It can only be instantiated by an instance of a derived type. Therefore the only types that should have access to a constructor are its derived types and hence protected makes much more sense than public. It more accurately describes the accessibility.
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