我試圖在一種方法中捕獲沒有輸入（輸入鍵）和無效輸入除 y/n 之外的所有內(nèi)容。我嘗試了兩種不同的方式（粘貼），但我無法同時(shí)使用“輸入鍵”和“錯(cuò)誤輸入 y/n”。感謝您的幫助。第一次嘗試：public static String askToContinue(Scanner sc) {String choice = "";boolean isValid = false;while (!isValid){System.out.print("Continue? (y/n): ");    if (sc.hasNext()){        choice = sc.next();        isValid = true;    } else {System.out.println("Error! "                + "This entry is required. Try again");        }    if (isValid && !choice.equals("y") || !choice.equals("n")) {        System.out.println("Error! Entry must be 'y' or 'n'. Try again");        isValid = false;    }   }    //sc.nextLine();  // discard any other data entered on the line    System.out.println();    return choice;   }           2nd attempt    public static String askToContinue(Scanner sc) {    System.out.print("Continue? (y/n): ");    String choice;    while (true) {choice = sc.next();    //?????????????????????????????????????????????????????        if (choice.length() == 0){ System.out.println("Error! "                + "This entry is required. Try again");            continue;        }        if (!(choice.equals("y") || choice.equals("n"))) {            System.out.println("Error! Entry must be 'y' or 'n'. Try                   again");            continue;        }        break;        }    sc.nextLine();  // discard any other data entered on the line    System.out.println();    return choice;    }