输入枚举以切换语句结果

Question

所以在这里我要求用户输入命中、停止、投降或退出。我将这些作为枚举，以及 NOTVALID。

enum Decisions

{
    HIT, STAND, SURRENDER, QUIT, PLAY, NOTVALID;
    // NOTVALID is used to re-ask to play again
}

因此，如果用户输入 "blah" 而不是有效选项之一，我希望它认为它是 NOTVALID 并执行 switch 语句中用于 NOTVALID 的代码。我怎样才能做到这一点？实际上，当我运行程序时 returns 错误：

Exception in thread "main" java.lang.IllegalArgumentException: No enum constant BlackJack.Decisions.BLAH

我可以做些什么来使任何不是其他枚举之一的东西成为 NOTVALID？

System.out.println("Do you want to hit, stand, surrender, or quit?");

        String decisionInput;

        decisionInput = keyboard.nextLine().toUpperCase();

        decision = Decisions.valueOf(decisionInput);

        switch (decision)
        {
            case HIT: 
                Random playerCard = new Random();

                cardPick = playerCard.nextInt(13);

                playerSum = playerSum + getCardValue(cardPick);

                System.out.println("Card: " + (Card.values()[cardPick]) + ". The sum of your hand is: " + playerSum + "."); 

                System.out.println("The hole card was " + (Card.values()[cardPick2]) + ". The house has: " + houseSum + ".");

                findWinner(playerSum, houseSum, decision);

                System.out.println("Do you want to play again? Type PLAY or QUIT.");

                decision = Decisions.valueOf(keyboard.nextLine().toUpperCase());

                break;

            case STAND:
            case SURRENDER:

                findWinner(playerSum, houseSum, decision);

                System.out.println("Do you want to play again? Type PLAY or QUIT.");

                decision = Decisions.valueOf(keyboard.nextLine().toUpperCase());

                break;

            case QUIT:

                System.out.println("Thanks for playing!");

                System.exit(0);

                break;

            case NOTVALID:

                System.out.println("Invalid input. Try again: hit, stand, surrender, or quit?");

                decision = Decisions.valueOf(keyboard.nextLine().toUpperCase());

            }   
        }
    }       
}

Answer 1

定义一个新方法，returns NOTVALID 用于无法识别的输入。最简洁的方法是捕获正在抛出的 IllegalArgumentException。

enum Decisions{
     HIT, STAND, SURRENDER, QUIT, PLAY, NOTVALID;

     public static Decisions asDecision(String input) {
         try {
             return Decisions.valueOf(input);
         } catch(IllegalArgumentException e) {
             return Decisions.NOTVALID;
         }
     }
}

如果这冒犯了您使用 try..catch 的敏感性，您可以自己手动完成。

enum Decisions{
         HIT, STAND, SURRENDER, QUIT, PLAY, NOTVALID;

         public static Decisions asDecision(String input) {
             for(Decisions d : values()) {
                 if(d.name().toLowerCase().equals(input.toLowerCase()) {
                     return d;
                 }
             }
             return Decisions.NOTVALID;
         }
    }

无论如何，请改用新方法。

在不允许定义新方法的情况下，您可以将您的作业包围在 try..catch 中，例如：

    String decisionInput;
    decisionInput = keyboard.nextLine().toUpperCase();
    try{
        decision = Decisions.valueOf(decisionInput);
    } catch(IllegalArgumentException e){
        decision = Decisions.NOTVALID;
    }
    // Rest of your code...

Answer 2

您可以使用 default: 而不是 NOTVALID。它类似于 else，在其他情况下，它将默认为该逻辑。

default:
    System.out.println("Invalid input. Try again: hit, stand, surrender, or quit?");
    decision = Decisions.valueOf(keyboard.nextLine().toUpperCase());

输入枚举以切换语句结果

Input of enums to switch statment outcomes

java

enums

switch-statement