Abstract Class and Interface for Java Intoductory course.pptx
- 1. Abstract Class Class Objectives: Why abstract class? How to Implement it? “Don’t be Hidden”
- 2. Java Abstract Class The abstract class in Java cannot be instantiated (we cannot create objects of abstract classes). We use the abstract keyword to declare an abstract class. For example,
- 3. An abstract class can have both the regular methods and abstract methods. For example,
- 4. Java Abstract Method A method that doesn't have its body is known as an abstract method. We use the same abstract keyword to create abstract methods. For example, If a class contains an abstract method, then the class should be declared abstract. Otherwise, it will generate an error. For example,
- 5. Java Abstract Class and Method Though abstract classes cannot be instantiated, we can create subclasses from it. We can then access members of the abstract class using the object of the subclass. For example,
- 6. Implementing Abstract Methods If the abstract class includes any abstract method, then all the child classes inherited from the abstract superclass must provide the implementation of the abstract method. For example,
- 7. Accesses Constructor of Abstract Classes An abstract class can have constructors like the regular class. And, we can access the constructor of an abstract class from the subclass using the super keyword. For example, Here, we have used the super() inside the constructor of Dog to access the constructor of the Animal. Note that the super should always be the first statement of the subclass constructor.
- 8. Java Abstraction • Abstraction is an important concept of object-oriented programming that allows us to hide unnecessary details and only show the needed information. • This allows us to manage complexity by omitting or hiding details with a simpler, higher-level idea.
- 9. Key Points to Remember •We use the abstract keyword to create abstract classes and methods. •An abstract method doesn't have any implementation (method body). •A class containing abstract methods should also be abstract. •We cannot create objects of an abstract class. •To implement features of an abstract class, we inherit subclasses from it and create objects of the subclass. •A subclass must override all abstract methods of an abstract class. However, if the subclass is declared abstract, it's not mandatory to override abstract methods. •We can access the static attributes and methods of an abstract class using the reference of the abstract class. For example,
- 10. Interface An interface is a fully abstract class. It includes a group of abstract methods (methods without a body). We use the interface keyword to create an interface in Java. For example,
- 11. Implementing an Interface Like abstract classes, we cannot create objects of interfaces. To use an interface, other classes must implement it. We use the implements keyword to implement an interface.
- 12. Implementing Multiple Interfaces Extending an Interface
- 13. Advantages of Interface in Java • Similar to abstract classes, interfaces help us to achieve abstraction in Java. • Interfaces provide specifications that a class (which implements it) must follow. • Interfaces are also used to achieve multiple inheritance in Java. For example,
- 14. default methods in Java Interfaces • If a large number of classes were implementing this interface, we need to track all these classes and make changes to them. This is not only tedious but error-prone as well. • To resolve this, Java introduced default methods. Default methods are inherited like ordinary methods.
- 15. private and static Methods in Interface • The Java 8 also added another feature to include static methods inside an interface. • With the release of Java 9, private methods are also supported in interfaces. We cannot create objects of an interface.