Advanced Programming in Java

1. Advanced Programming in Java SadeghAliakbary Sharif University of Technology Fall 2012

2. Agenda • Enumerations • Static Import • Annotation Sharif University of Technology

3. Enumerations

4. Enumerations • Suppose you have a class with a few instances • Example: • Student Type : <BS, MS, PhD> • SMS Status : <Sent, Delivered, Not Delivered, Not Sent> • Color : <Blue, Green, Black, Red> • How do you implement it? • The class should not be inherited • The instances are limited: no further instances Sharif University of Technology

5. An Implementation finalclass Color{ publicstaticfinal Color Black = new Color(1); publicstaticfinal Color Blue = new Color(2); publicstaticfinal Color Green = new Color(3); publicstaticfinal Color Red = new Color(4); privateintcolor; private Color(inti) { this.color = i; } } Applications of a private constructor Sharif University of Technology

6. Java enum • Java introduces enumerations for this purpose • Enumerated Data Type • A simple class • enum keyword instead of class or interface • Comma seperatedenum instances • enum instances are constant enum Color { Black, Blue, Green, Red } Sharif University of Technology

7. Enum enum Color { Black, Blue, Green, Red } finalclass Color{ publicstaticfinal Color Black = new Color(); publicstaticfinal Color Blue = new Color(); publicstaticfinal Color Green = new Color(); publicstaticfinal Color Red = new Color(); } Sharif University of Technology

8. Enum Sample enum Shape { Rectangle, Circle, Square } enumStudentType{ BS, MS, PhD } Sharif University of Technology

9. Using Enums Color color = Color.Black; Shape shape = Shape.Circle; show(shape, color); ... privatestaticvoid show (Shape shape, Color color) { //show a shape with this color ... } Sharif University of Technology

10. Enum Characteristics • enum types are implicitly final • Can not be a super-class • Because they declare constants that should not be modified • Instances are constants • enum constants are implicitly public,static and final • No new instances can be created • object instantiation of enum types with operator new results in a compilation error. Sharif University of Technology

11. Enum • Enum can be a more complex class • With many constructors • And fields • And methods Sharif University of Technology

12. enum Shape { Rectangle(1), Circle(2), Square(3); privateintnumber; Shape(inti){ number= i; } publicintgetNumber(){ returnnumber; } } Shape shape = Shape.Circle; print (shape.getNumber()); shape = Shape.valueOf("Rectangle"); print(shape.getNumber()); Shape[] shapesArray = Shape.values(); for (Shape s : shapesArray) { print(s.name()); } try{ shape = Shape.valueOf("Pyramid"); }catch(Exception exp){ print("Pyramid is not included in Shape"); } Sharif University of Technology

13. Static Import • In order to access static members • Qualify references with the class they came from. • For example: double r = Math.sin(Math.PI * theta); • static import allows unqualified access to static members • without inheriting from the type containing the static members import static java.lang.Math.PI; or import static java.lang.Math.*; double r = sin(PI * theta); Sharif University of Technology

14. Annotation • An annotation is a special form of metadata • Added to Java source code • Classes, methods, variables, parameters and packages may be annotated • Unlike Javadoc tags, Java annotations can be reflective • They can be embedded in class files (byte code) • May be retained by the Java VM at run-time • Example • @Override, @Deprecated, @ SuppressWarnings, … Sharif University of Technology

15. Ergonomy

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