Java program for abstract class and method

The interface is similar to an abstract class as it is the grouping of abstract methods. When a class implements the interface, all the abstract methods within the interface are inherited. The interface might also contain default methods, constants, and static methods. The method bodies of only the default and the static methods are present. While in the case of an interface only those behaviours of an object are present, those are implemented by the class. A class has to define all the methods of the interface that it implements.

Only for an abstract class, the methods are not required to be defined by the class. An interface is similar to a Java abstract class in the following ways:. An interface is different from a Java abstract class in the following ways:. Total abstraction is provided through the use of an interface. By default, all the methods within an interface are abstract and public.

This means there is nobody of the methods in an interface and all the fields are static, public, and final. More than one interface can be implemented by a class. The keyword is used in the class declaration. An example of a code showing the implementation of an interface in Java is shown below.

A code applying the implementation of multiple interfaces is shown below. Although abstraction in Java can be achieved through Java abstract class, interfaces are used as they contain final, public and static variables. However, non-final variables may be present in an abstract class. If both the Java interface and Java abstract class are used to achieve abstraction, when should an interface and abstract class be used?

In this example, Bike is an abstract class that contains only one abstract method run. Its implementation is provided by the Honda class. In this example, Shape is the abstract class, and its implementation is provided by the Rectangle and Circle classes. Mostly, we don't know about the implementation class which is hidden to the end user , and an object of the implementation class is provided by the factory method.

A factory method is a method that returns the instance of the class. We will learn about the factory method later. In this example, if you create the instance of Rectangle class, draw method of Rectangle class will be invoked. An abstract class can have a data member, abstract method, method body non-abstract method , constructor, and even main method. The abstract class can also be used to provide some implementation of the interface. In such case, the end user may not be forced to override all the methods of the interface.

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Abstract class is used to provide abstraction. Lets see how abstract class is used to provide abstraction. Here by casting instance of Car type to Vehicle reference, we are hiding the complexity of Car type under Vehicle. Now the Vehicle reference can be used to provide the implementation but it will hide the actual implementation process. Abstract methods are usually declared where two or more subclasses are expected to do a similar thing in different ways through different implementations.

These subclasses extend the same Abstract class and provide different implementations for the abstract methods. Abstract classes are used to define generic types of behaviors at the top of an object-oriented programming class hierarchy, and use its subclasses to provide implementation details of the abstract class. Remember Me. Create a new account.

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