java - 连续生成随机枚举值而不会两次获得相同的值

Question

我有一个要随机化的枚举团队。所以我有：

public enum Teams { TEAM1, TEAM2, TEAM3, TEAM4, TEAM5, TEAM6; }

然后我有一个随机方法来随机生成值：

public static Teams getRandomTeam() {
    return Teams.values()[(int) (Math.random() * Teams.values().length)];
}

它确实返回了一个随机生成的团队，但是我需要，一旦生成了一个团队，比如 TEAM2，它就不能再次生成。

我在用着：

System.out.println("The team is " + getRandomTeam());
System.out.println("The team is " + getRandomTeam());
System.out.println("The team is " + getRandomTeam());
System.out.println("The team is " + getRandomTeam());
System.out.println("The team is " + getRandomTeam());
System.out.println("The team is " + getRandomTeam());

（我知道这是错误的，因为它一遍又一遍地调用该方法。

在我运行程序的那一刻，输出可能是：

队伍是：TEAM2

队伍是：TEAM2

队伍是：TEAM4

队伍是：TEAM2

队伍是：TEAM3

队伍是：TEAM2

但是我需要我的程序只输出一次枚举值。谢谢

Answer 1

只需使用Collections.shuffle。

List<Team> teams = new ArrayList<>();
Collections.addAll(teams, Team.values());
Collections.shuffle(teams);

Answer 2

最好对集合进行洗牌并逐个返回元素。

  private static List<Teams> tList;

  private static void regenerateList() {
      tList = new ArrayList<Teams>(Arrays.asList(Teams.values()));
      Collections.shuffle(tList);
  }

  public static Teams getRandomTeam() {
      if (tList.size() > 0) {
         return tList.remove(0);
      } else {
          //handle as you wish: return null or regenerate the list 
         regenerateList();
         return getrandomTeam();
      }
  }

Answer 3

那这个呢？它是递归的！

public static enum TEAMS {
    TEAM1, TEAM2, TEAM3, TEAM4, TEAM5, TEAM6;
}

TEAMS[] teams = TEAMS.values();
Random rnd = new Random();

public TEAMS getnextRandomTeam() {
    int indx = rnd.nextInt(teams.length);
    TEAMS t = teams[indx];
    teams[indx] = null;
    return t == null ? getnextRandomTeam() : t;
}

Answer 4

使用 Collections shuffle 方法：

List<Teams> teams = new ArrayList<Teams>(Arrays.asList(Teams.values()));
int index = Integer.MAX_VALUE;

public Teams getRandomTeam() {
    if (index >= teams.size()) {
        Collections.shuffle(teams);
        index = 0;
    }
    return teams.get(index++);
}

此代码以随机顺序返回所有值，并在用尽时重置列表以无限期地重复该过程。