5- Overriding and Abstraction In Java
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The document discusses object-oriented programming concepts in Java including overriding, abstraction, the final and super keywords, abstract classes and interfaces. It provides rules for method overriding in Java and explains that overriding allows a subclass to provide specific implementations of methods declared in the parent class. It also describes how abstraction hides internal details and shows only important functionality to the user, and that abstract classes can contain both abstract and non-abstract methods while interfaces can only contain abstract methods.
5- Overriding and Abstraction In Java
- 1. P.1 Overriding and Abstraction ghadeer-al-hasan ghadeerof@gamil.com
- 2. Java Overriding: P.2 Overriding means to override the functionality of an existing method. A subclass implement a parent class method based on its requirement.
- 3. Java Overriding Cont. : P.3
- 4. Java Overriding Cont. : P.4
- 5. Java Overriding Cont. : P.5 Rules for method overriding: The argument list should be exactly the same as that of the overriding method. The return type should be the same of the return type declared in the original override method in the superclass. If the supper class method is declared public then the overriding method in the subclass cannot be either private or protected A method declared final cannot be overridden. A method declared static cannot be overridden. If a method cannot be inherited, then it cannot be overridden. A subclass in a different package can only override the non-final methods declared public or protected.
- 7. super keyword : P.7 The super keyword in java is a reference variable that is used to refer Immediate parent class object. 1) Super is used to refer immediate parent class instance variable.
- 8. super keyword Cont. : P.8 2) Super is used to invoked parent class constructor: super() is added in each class constructor automatically by compiler.
- 9. super keyword Cont. : P.9
- 10. super keyword Cont. : P.10 3) super can be used to invoked parent class method:
- 11. super keyword Cont. : P.11
- 13. final keyword : P.13 The final keyword is used to restrict the user, cam be used in many context: Variable Method class 1) final variable: if you make any variable as final, you cannot change the value of final variable
- 14. final keyword Cont. : P.14 2)If you make any method as final , you cannot override it.
- 15. final keyword Cont. : P.15 2)If you make any method as final , you cannot override it, but is inherited.
- 16. final keyword Cont. : P.16 3)If you make any class as final, you cannot extend it.
- 17. final keyword Cont. : P.17 A final variable that is not initialized at the time of declaration can be initialize only in constructor.
- 18. final keyword Cont. : P.18 A static final variable that is not initialized at the time of declaration can be Initialized only in static block.
- 19. final keyword Cont. : P.19 If you declare any parameter as final, you cannot change the value of it. You cannot declare constructor final because it is never inherited.
- 20. P.22 Abstraction
- 21. Abstraction P.21 • Is a process of hiding the implementation details and showing Only functionality to the user. • It shows only important things to the user and hides the internal details. Abstract class: • A class that is declared with abstract keyword, is know as abstract class • It can have abstract and non abstract method. • It needs to be extends and its method implemented, it cannot be instantiated Abstract method: A method that is declared as abstract and does not have body.
- 22. Abstraction Example : P.22
- 25. P.25Notes : Note: If there is any abstract method in a class, that class must be abstract. If you are extending any abstract class that have abstract method, you must either provide the implementation of the method or make this class abstract.
- 26. P.26 Interfaces
- 27. P.27Interfaces: Is a mechanism to achieve fully abstraction. There can be only abstract methods . Used to achieve fully abstraction and multiple inheritance . Represents IS-A relationship. Cannot be instantiated just like abstract class. P.S: The java compiler adds public and abstract keywords before the interface method And public, static and final keywords before data members.
- 28. P.28Classed and interfaces: class class interface class interface interface extends extendsimplements
- 29. P.29Multiple inheritance: interface class implements interface interface interface extends interface
- 32. P.32Instance initializer block: Is used to initialize the instance data member. It run each time when object of the class is created.
- 33. P.33Instance initializer block: The java compiler copies the code of instance initializer block in every constructor. compiler
- 34. P.34Instance initializer block Cont.: