将用户输入的字符串限制为字母和数字值

Question

基本上，我的情况要求我检查在一种情况下由用户从键盘输入定义的字符串是否仅为字母字符，而在另一种情况下仅为数字。这是用Java编写的。

我当前的代码：

switch (studentMenu) {
                case 1: // Change all four fields
                    System.out.println("Please enter in a first name: ");

                    String firstNameIntermediate = scan.next();
                    firstName = firstNameIntermediate.substring(0,1).toUpperCase() + firstNameIntermediate.substring(1);
                    System.out.println("Please enter in a middle name");
                    middleName = scan.next();
                    System.out.println("Please enter in a last name");
                    lastName = scan.next();
                    System.out.println("Please enter in an eight digit student ID number");
                    changeID();
                    break;
                case 2: // Change first name
                    System.out.println("Please enter in a first name: ");
                    firstName = scan.next();
                    break;
                case 3: // Change middle name
                    System.out.println("Please enter in a middle name");
                    middleName = scan.next();
                    break;
                case 4: // Change last name
                    System.out.println("Please enter in a last name");
                    lastName = scan.next();
                case 5: // Change student ID:
                    changeID();
                    break;
                case 6: // Exit to main menu
                    menuExit = true;
                default:
                    System.out.println("Please enter a number from 1 to 6");
                    break;
            }
        }
    }

public void changeID() {
    studentID = scan.next();
    }

我需要确保StudentID仅是数字，并且每个名称段都是字母。

Answer 1

java.util.Scanner已经可以使用方法检查下一个标记是否具有给定的模式/类型hasNextXXX。

这是一个boolean hasNext(String pattern)使用正则表达式用于验证下一个标记仅由字母组成的示例[A-Za-z]+：

    Scanner sc = new Scanner(System.in);
    System.out.println("Please enter letters:");
    while (!sc.hasNext("[A-Za-z]+")) {
        System.out.println("Nope, that's not it!");
        sc.next();
    }
    String word = sc.next();
    System.out.println("Thank you! Got " + word);

这是一个示例会话：

Please enter letters:
&#@#$
Nope, that's not it!
123
Nope, that's not it!
james bond
Thank you! Got james

要验证下一个令牌是可以转换为的数字，请int使用hasNextInt()，然后使用nextInt()。