Q&A : What is an abstract class, and when should it be used?

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In the interface, it is compulsory to initialize the variable at the time of the declaration. Let's look at an example of an abstract class, and an abstract method.

It can also have abstract methods that look to the extending class to implement, but it certainly can have implementation. You could have just used an ordinary class.

Java abstract class program

It has static constants and abstract methods. The interface in Java is a mechanism to achieve abstraction. There can be only abstract methods in the Java interface, not method body. It is used to achieve abstraction and multiple inheritance in Java. In other words, you can say that interfaces can have abstract methods and variables. It cannot have a method body. It cannot be instantiated just like the abstract class. Since Java 8, we can have default and static methods in an interface. Since Java 9, we can have private methods in an interface. There are mainly three reasons to use interface. How to declare an interface. An interface is declared by using the interface keyword. It provides total abstraction; means all the methods in an interface are declared with the empty body, and all the fields are public, static and final by default. A class that implements an interface abstract class in java implement all the methods declared in the interface. } Java 8 Interface Improvement Since Java 8, interface can have default and static methods which is discussed later. Internal addition by the compiler The Java compiler adds public and abstract keywords before the interface method. Moreover, it adds public, static and final keywords before data members. In other words, Interface fields are public, static and final by default, and the methods are public and abstract. The relationship between classes and interfaces As shown in the figure given below, a class extends another class, an interface extends abstract class in java interface, but a class implements an interface. Java Interface Example In this example, the Printable interface has only one method, and its implementation is provided in the A6 class. Hello Java Interface Example: Drawable In this example, the Drawable interface has only one method. Its implementation is provided by Rectangle and Circle classes. In a real scenario, an interface is defined by someone else, but its implementation is provided by different implementation providers. Moreover, it is used by someone else. The implementation part is hidden by the user who uses the interface. As we have explained in the inheritance chapter, multiple inheritance is not supported in the case of class because of ambiguity. However, it is supported in case of an interface because there is no ambiguity. It is because its implementation is provided by the implementation class. For example: interface Printable void print ; interface Showable extends Printable void show ; class TestInterface4 implements Showable{ public void print {System. Mail us on hr javatpoint.

If all employees are either salaried or hourly, for example, it makes sense to create an abstract Employee class and then use it as the base class for the SalariedEmployee and HourlyEmployee subclasses. We cannot declare interface variable with the following modifiers- private, protected, transient, volatile There is no restriction on the abstract class variable modifier. In Java the same effect can be achieve by using a composition of classes instead of inheritance from broadly defined abstract classes. The abstract class states the class characteristics and methods for implementation, thus defining a whole interface. Couple of days back I wrote an article on basic on?