1. Enumerations & Annotations
Advanced Programming in Java
Enumerations & Annotations
Mehdi Einali

2. enum

3. Enumerations Suppose you have a type with a few instances Example:
Student Type : <BS, MS, PhD>
SMS Status : <Sent, Delivered, Not Delivered, Not Sent>
WeekDay: <Saturday, Sunday, Monday, …>
How do you implement it?
The class should not be inherited
The instances are limited: no further instances

4. Bad Implementation1 final class WeekDay{
public static final WeekDay Saturday= new WeekDay(1);
public static final WeekDay Sunday= new WeekDay(2);
public static final WeekDay Monday = new WeekDay(3);
public static final WeekDay Tuesday= new WeekDay(4);
private int code;
private Color(int i) {
this.code = i; }

5. Bad Implementation2 interface WeekDay{ int Saturday= 1; int Sunday= 2;
int Monday = 3;
int Tuesday= 4; }
class Client implements WeekDay{
public void foo(){

6. Java enum Java introduces enumerations for this purpose
Enumerated Data Type
A simple class
enum keyword instead of class or interface
Comma seperated enum instances
enum instances are constant

7. sample enum Shape { Rectangle, Circle, Square } enum StudentType{
BS, MS, PhD

8. use
Color color = Color.Black; Shape shape = Shape.Circle; show(shape, color); ... private static void show ( Shape shape, Color color) { //show a shape with this color }

9. 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.

10. Switch on enum

11. More than constant Enum can be a more complex class
With many constructors
And fields
And methods

13. Implicitly static final

14. Implicit methods

16. annotations

17. Annotation

18. What is 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, …

19. Why Annotation? Enables “declarative programming” style
Less coding since tool will generate the boliler plate code from annotations in the source code
Easier to change
Eliminates the need for maintaining "side files" that must be kept up to date with changes in source files
Information is kept in the source file
example) Eliminate the need of deployment descriptor

20. {"name":"Ali Karimi","number":"7"}
sample
{"name":"Ali Karimi","number":"7"}

21. 3 different types
@Override

22. Write annotation

23. use

24. end