Java 将字符串分配给 double 时编译器抛出 InputMismatchException

您可以使用以下方法确定String是否包含空格字符.

boolean containsSpace(String string) {
    for (char character : string.toCharArray()) {
        switch (character) {
            case ' ', '\t', '\n', '\r', '\f' -> {
                return true;
            }
        }
    }
    return false;
}

此外，您还需要使用String.equals方法测试name值，而不是使用==相等运算符.

if (name.equals("")) error = true;

此外，main方法需要一个String数组或String个varargs参数才有效.

public static void main(String[] args)

以下是我将如何执行这项任务的快速演示.

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    
    String name;
    while (true) {
        System.out.print("Name: ");
        name = scanner.nextLine();
        if (!containsSpace(name))
            break;
        System.out.println("Name contains white-space.  Re-enter.");
    }
    
    double amount;
    while (true) {
        System.out.print("Amount: ");
        try {
            amount = Double.parseDouble(scanner.nextLine());
            break;
        } catch (NumberFormatException exception) {
            System.out.println("Invalid amount.  Re-enter.");
        }
    }
    
    System.out.printf("Name is '%s'%n", name);
    System.out.printf("Amount is %,f%n", amount);
}