Which design pattern is used to implement enumerations?

The pattern often used for implementing enumerations (enums) is the "Typesafe Enum" pattern. In Java, before the introduction of the built-in enum (before Java 5), this pattern was implemented by creating a class with a private constructor and a set of public static final instances of that class.

Example:

public class Day {
    public static final Day MONDAY = new Day("Monday");
    public static final Day TUESDAY = new Day("Tuesday");

    private String name;

    private Day(String name) {
        this.name = name;
    }

    public String toString() {
        return name;
    }
}

With the advent of enum in Java 5, it is recommended to use the built-in enum, which implements this pattern at the language level.