Java Tutorial/Data Type/enum

Comparing Enumeration Values

public class MainClass {
  enum Season {
    spring, summer, fall, winter
  };
  public static void main(String[] arg) {
    Season season = Season.summer;
    if (season.equals(Season.spring)) {
      System.out.println("It is Spring.");
    } else {
      System.out.println("It isn\"t Spring!");
    }
  }
}

It isn"t Spring!

Enumeration Fundamentals

An enumeration is created using the new enum keyword.

enum Week {
  Monday, Tuesday, Wednesday, Thursday, Friday, Saturaday, Sunday
}

Value of aWeekDay: Monday

Enums in a Class

public class Shape {
  private enum ShapeType {
    RECTANGLE, TRIANGLE, OVAL
  };
  private ShapeType type = ShapeType.RECTANGLE;
  public String toString() {
    if (this.type == ShapeType.RECTANGLE) {
      return "Shape is rectangle";
    }
    if (this.type == ShapeType.TRIANGLE) {
      return "Shape is triangle";
    }
    return "Shape is oval";
  }
}

Enum type field

public class ShirtTest {
  public static void main(String[] args) {
    Shirt shirt1 = new Shirt();
    shirt1.setName("new name");
    shirt1.setBid(23.5);
    shirt1.setSize(Size.M);
    System.out.println(shirt1);
  }
}
class Shirt {
  private String name;
  private double bid;
  private Size size;
  public Shirt() {
  }
  public void setName(String name) {
    this.name = name;
  }
  public String getName() {
    return name;
  }
  public void setBid(double bid) {
    this.bid = bid;
  }
  public double getBid() {
    return bid;
  }
  public void setSize(Size size) {
    this.size = size;
  }
  public Size getSize() {
    return size;
  }
  @Override
  public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append(" Name: " + this.getName() + ",");
    sb.append(" Bid: " + this.getBid() + " Dollar,");
    sb.append(" Size: " + this.getSize());
    return sb.toString();
  }
}
enum Size {
  S, M, L, XL, XXL, XXXL;
}

enum type with its own method

public class SizeIterator {
  public static void main(String[] args) {
    Size[] sizes = Size.values();
    for (Size s : sizes) {
      System.out.println(s);
    }
  }
}
enum Size implements Countable {
  S, M, L, XL, XXL, XXXL;
  @Deprecated
  public Size increase() {
    Size sizes[] = this.values();
    int pos = this.ordinal();
    if (pos < sizes.length - 1)
      pos++;
    return sizes[pos];
  }
}
interface Countable {
  public Size increase();
}

enum with switch

public class SizeSwitch {
    
    public static void main(String[] args) {
        Size size = Size.XL;
        switch(size){
            case S:    
                System.out.println("S");
                break;
            case M:    
                System.out.println("M");
                break;
            case L:    
                System.out.println("L");
                break;
            case XL:    
                System.out.println("XL");
                break;
            case XXL:    
                System.out.println("XXL");
                break;
            case XXXL:    
                System.out.println("XXXL");
                break;                
        }
    }
}

enum Size {
  S, M, L, XL, XXL, XXXL;
}

equals and = operator for enum data type

enum Week {
  Monday, Tuesday, Wednesday, Thursday, Friday, Saturaday, Sunday
}
public class MainClass {
  public static void main(String args[]) {
    Week day1, day2, day3;
    day1 = Week.Monday;
    day2 = Week.Monday;
    day3 = Week.Monday;
    if(day1.equals(day2))
      System.out.println("Error!");
    if(day1.equals(day3))
      System.out.println(day1 + " equals " + day3);
    if(day2 == day3)
      System.out.println(day2 + " == " + day3);

  }
}

Error!
Monday equals Monday
Monday == Monday

How to define an enumeration

1. To define a new type, Day.
2. Variable of type Day can only store the values specified between the braces.
3. Monday, Tuesday, ... Sunday are called enumeration constants.
4. These names will correspond to integer values, starting from 0 in this case.

public class MainClass {
  enum Day {
    Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday
  }
  public static void main(String[] args) {
    Day yesterday = Day.Thursday;
    Day today = Day.Friday;
    Day tomorrow = Day.Saturday;
    System.out.println("Today is " + today);
    System.out.println("Tomorrow will be " + tomorrow);
    System.out.println("Yesterday was " + yesterday);
  }
}

Today is Friday
Tomorrow will be Saturday
Yesterday was Thursday

Two enumeration constants can be compared for equality by using the == relational operator

enum Week {
  Monday, Tuesday, Wednesday, Thursday, Friday, Saturaday, Sunday
}
public class MainClass {
  public static void main(String args[]) {
    Week aWeekDay;
    aWeekDay = Week.Monday;
    // Output an enum value.
    System.out.println("Value of aWeekDay: " + aWeekDay);
    System.out.println();
    aWeekDay = Week.Friday;
    // Compare two enum values.
    if (aWeekDay == Week.Friday)
      System.out.println(" Friday.\n");
  }
}

Value of aWeekDay: Monday
 Friday.

uses an enum, rather than interface variables, to represent the answers.

import java.util.Random;
enum Answers {
  NO, YES, MAYBE, LATER, SOON, NEVER
}
class Question {
  Random rand = new Random();
  Answers ask() {
    int prob = (int) (100 * rand.nextDouble());
    if (prob < 15)
      return Answers.MAYBE; // 15%
    else if (prob < 30)
      return Answers.NO; // 15%
    else if (prob < 60)
      return Answers.YES; // 30%
    else if (prob < 75)
      return Answers.LATER; // 15%
    else if (prob < 98)
      return Answers.SOON; // 13%
    else
      return Answers.NEVER; // 2%
  }
}
class AskMe {
  static void answer(Answers result) {
    switch (result) {
    case NO:
      System.out.println("No");
      break;
    case YES:
      System.out.println("Yes");
      break;
    case MAYBE:
      System.out.println("Maybe");
      break;
    case LATER:
      System.out.println("Later");
      break;
    case SOON:
      System.out.println("Soon");
      break;
    case NEVER:
      System.out.println("Never");
      break;
    }
  }
  public static void main(String args[]) {
    Question q = new Question();
    answer(q.ask());
    answer(q.ask());
    answer(q.ask());
    answer(q.ask());
  }
}