OBJECT ORIENTED PROGRAMMING IN JAVA

Transcription

1 OBJECT ORIENTED PROGRAMMING IN JAVA MIKHAIL MARKOV DEPARTMENT OF COMPUTING AND SOFTWARE MCMASTER UNIVERSITY SFWRENG/COMPSCI 2S03 (FALL 2015) TUTORIAL 5

2 Contacts Graduate Teaching Assistants: Akhil Krishnan: Michael Liut: Mikhail Markov: Undergraduate Teaching Assistants: Jemar Jones: Wenqiang Chen:

3 Outline Class and Object Class and Object: example Class bird example: class definition Class bird example: objects Class bird example: class definition with constructors Class bird example: objects with constructors Encapsulation Encapsulation: example Immutability Immutability: example of changing the values Immutability: the same example with the final keyword Method Overloading Method Overloading: example

4 Class and Object Class - the blue-print that describes the possible behaviours and states that object of its type support. Object - an instance of the class (the houses built from the blue-print). Have specific values of the states and behaviours.

5 Class and Object: example Example Class: bird State: size, colour, family, etc. Behavior: flying, swimming, eating, etc. Objects: sparrow, duck, goose, etc. Object_Sparrow States: size = small, colour = browngrey, family = Passeridae; Sparrow Behavior: flying

6 Class bird example: class definition

7 The result: Class bird example: objects

8 Class bird example: objects We can manually assign the values of the states to every object. But what if we have hundreds of the similar objects?? Can we do better?

9 Class bird example: objects Yes we can! We need to use constructors! With multiple constructors we can create the objects with all or just several same states.

10 Class bird example: class definition with constructors

11 Class bird example: objects with constructors

12 Class bird example: objects with constructors The result:

13 Encapsulation What will happen if we ll change the modifier of the class states from public to private and we ll try to assign the values of the states from the main function?

14 Encapsulation The result is

15 Encapsulation The result is an exception (doesn t compile) as the states of the class with the modifier private becomes not visible. So it can t be changed somehow from another class.

16 Encapsulation The benefit of encapsulation is that we can, for instance, define the possible values of the states. This values can t be changed to another (not in our list) like it s possible with the public modifier. Let s look at the example.

17 Encapsulation: example

18 The result: Encapsulation: example

19 Immutability In general we can change the values of the states multiple times. Let s look at the example.

20 Immutability: example of changing the values

21 Immutability: example of changing the values The result:

22 Immutability: the same example with the final keyword Let s add final keyword to add immutability and run the same code. The result is an exception: But if we ll comment the change: The code works:

23 Method Overloading Method overloading in used when several methods of the same class have the same name but different number or type of the parameters.

24 Method Overloading: example

25 The result: Method Overloading: example