Java Programming/Keywords/enum

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enum is a keyword since Java 1.5.

This keyword defines a group of constants.

For example:

Computer code
/** Grades of courses */
  enum Grade { A, B, C, D, F };
  // ...
  private Grade gradeA = Grade.A;


This enumeration constant then can be passed in to methods:

Computer code
student.assignGrade(gradeA);
  /**
   * Assigns the grade for this course to the student
   * @param GRADE  Grade to be assigned
   */

  public void assignGrade(final Grade GRADE) {
    grade = GRADE;
  }


An enumeration may also have parameters:

Computer code
public enum DayOfWeek {
  /** Enumeration constants */
  MONDAY(1), TUESDAY(2), WEDNESDAY(3), THURSDAY(4), FRIDAY(5), SATURDAY(6), SUNDAY(0);

  /** Code for the days of the week */
  private byte dayCode = 0;

  /**
   * Private constructor
   * @param VALUE  Value that stands for a day of the week.
   */

  private DayOfWeek(final byte VALUE) {
    dayCode = java.lang.Math.abs(VALUE%7);
  }
 
  /**
   * Gets the day code
   * @return  The day code
   */

  public byte getDayCode() {
    return dayCode;
  }
}


It is also possible to let an enumeration implement interfaces other than java.lang.Comparable and java.io.Serializable, which are already implicitly implemented by each enumeration:

Computer code
public enum DayOfWeek implements Runnable {
  MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY;
 
  /**
   * Run method prints all elements
   */

  public void run() {
    System.out.println("name() = " + name() +
      ", toString() = \"" + toString() + "\"");
  }
}