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Enum Members

layout: default title: enum Member

Since an enum is really a class, you are allowed to provide your own methods and fields in the enum declaration.

Fields and Methods

We can give the enum fields and methods, including constructors.

  • These come after the constant declarations.

This version of Day has a field for the name, and a toString() to print out that value.

public enum Day2 {
  // ...

  final private String name;

  @Override
  public String toString() {
    return name;
  }

  public String getName() {
    return name;
  }
}

Practice Exercise

enum fields are not implicitly final.

enum Constructors

We can initialize the field for each constant by providing a constructor.

Call the constructor when declaring the constant. * However, the constructor is still declared after the constants.

public enum Day2 {
  // Constants must be first
  SUNDAY("Sunday"),   // calling constructor
  MONDAY("Monday"),
  TUESDAY("Tuesday"),
  WEDNESDAY("Wednesday"),
  THURSDAY("Thursday"),
  FRIDAY("Friday"),
  SATURDAY("Saturday");

  Day2(String d){
    name = d;
  }

  final private String name;

  @Override
  public String toString() {
    return name;
  }

  public String getName() {
    return name;
  }
}
The constructor cannot be declared public or protected.

Practice Exercise

In an enum declaration, a constructor declaration with no access modifiers is private.1


Drill

EnumeratedTypes/com.example.enums.drills.cards

  • Create a public enum called Suit with the constants (in order) HEARTS, SPADES, CLUBS, DIAMONDS.
  • Add a private name field to Suit.
  • Add a one-arg constructor to Suit and set the name fields to Hearts, Spades, Clubs, Diamonds.
  • Override the toString method to output this name.
  • Create a public enum called Rank with the constants (in order) TWO, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT, NINE, TEN, JACK, QUEEN, KING, ACE.
  • Add a private value field to Rank.
  • Add a one-arg constructor to Rank and set the value field to 2-10 for numbers, 10 for JACK, QUEEN, and KING, and 11 for ACE.
  • Add a getValue() method to return the value.
  • Uncomment the code in CardTest to test your enums.

[1] https://docs.oracle.com/javase/specs/jls/se8/html/jls-8.html#jls-8.9.2

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