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01-class-and-objects java code in the .pdf
- 1. Object Oriented Programming Budditha Hettige Department of Computer Science
- 2. Overview • Introduction to OOP • Class and Objects • Constructors • Encapsulation • Composition • Inheritance • Polymorphism • Interfaces • Packages • Exception handling • File Handling • GUI Programming • OOP Software development 2 7/11/2015 Budditha Hettige (budditha@yahoo.com)
- 3. Introduction (OOP) • OOP is a programming paradigm that represents concepts as "objects" that have data fields (attributes that describe the object) and associated procedures known as methods 3
- 4. Advantages of OOP • Provides a clear modular structure for programs • OOP makes it easy to maintain and modify existing code (new objects can be created with small differences to existing ones) • OOP provides a good framework for code libraries • Software components can be easily adapted and modified by the programmer. 4
- 6. Exercise • Identify suitable state and behaviors (Attributes and methods) for the following – Student – Bank Account – Book – Employee – Sales Summary – Course – Result 7/11/2015 Budditha Hettige (budditha@yahoo.com) 6
- 7. Concepts of OOP • Objects • Classes • Encapsulation • Inheritance • Polymorphism • Data Abstraction 7
- 8. What is an Objects? • Object is a software bundle of related state and behavior • Characteristics: – state and behavior 8
- 9. What is a class? • A Java class is a group of Java methods and variables • Object is an instance of a class • Example class Person { // Methods // Variables } 9
- 10. Example • Create a Java Class Account with suitable methods and variables 7/11/2015 Budditha Hettige (budditha@yahoo.com) 10
- 11. Class Modifiers • Public • Abstract • Final • Default (none) 11
- 12. Java Programming: OOP 12 Class Modifiers • public: anyone can create an object of the defined class. – only one public class per file, must have same name as the file (this is how Java finds it!). • default: is non-public (if you don't specify "public").
- 13. Java Programming: OOP 13 Class Modifiers • abstract: modifier means that the class can be used as a superclass only. – no objects of this class can be created. • final: if its definition is complete and no subclasses are desired or required – a final class never has any subclasses, the methods of a final class are never overridden
- 14. Field Modifiers • public • protected • private • none or package or default • Static • Final 14
- 15. Java Programming: OOP 15 Field Modifiers • public: any method (in any class) can access the field. • protected: any method in the same package can access the field, or any derived class. • private: only methods in the class can access the field. • Default: is that only methods in the same package can access the field.
- 16. Java Programming: OOP 16 Field Modifiers • Static: Fields declared static are called class fields (class variables). others are called instance fields. There is only one copy of a static field, no matter how many objects are created. • Final:class and instance variables (static and non- static fields) may be declared final. The keyword final means: once the value is set, it can never be changed – static final int BUFSIZE=100; – final double PI=3.14159;
- 17. Method Modifiers • public • protected • none or package or default • private • final • abstract • static • native • synchronized 17
- 18. Java Programming: OOP 18 Method Modifiers • private/protected/public: – same idea as with fields. • abstract: no implementation given, must be supplied by subclass. – the class itself must also be declared abstract
- 19. Java Programming: OOP 19 Method Modifiers • static: the method is a class method, it doesn't depend on any instance fields or methods, and can be called without first creating an object. • final: the method cannot be changed by a subclass (no alternative implementation can be provided by a subclass).
- 20. Java Programming: OOP 20 Method Modifiers • native: the method is written in some local code (C/C++) - the implementation is not provided in Java. • synchronized: only one thread at a time can call the method.
- 21. Java Programming: OOP 21 Method Overloading • You can overload methods: – same method name, different parameters. – you can't just change return type, the parameters need to be different. • Method overloading is resolved at compile time. int CounterValue() { return counter; } double CounterValue() { return (double) counter; } Won't Work!
- 22. All Possible Combinations of Features and Modifiers 22 Modifier Class Variable Method public yes yes yes protected no yes yes None (default) yes yes yes private no yes yes final yes yes yes abstract yes no yes static no yes yes native no no yes transient no yes no volatile no yes no synchronized no no yes strictfp yes no yes
- 23. Example • Create a class “Student” with following methods – print(); – input() • Create a class “Length” with following methods – Print() – input() – Add(Lenth1, Length2) 23
- 24. Example contd. • Create a class Name with 3 attribute (First name, middle name and last name) and include following methods – Print(); – input() • Create a class name Date with 3 attribute (Day, Month and year) and include following methods – print() – Input() – printFormat1() // 23.5.2015 – PrintFormat2() // 23rd May 2015 24