我该如何在while循环中重复“输入分数或等级”的语句

您需要在第一个循环中添加另一个while循环，如果我理解正确的话，您想在输入更改后更改主题吗？如果是这样，那么它将起作用：

public static void main(String args[])
    {
        Scanner s = new Scanner(System.in);
        System.out.println("Here is Subject list");
        System.out.println("1-Physics");
        System.out.println("2-Math");
        System.out.println("3-computer");

        setSubject:
        while (true)
        {
            System.out.println("Enter subject number here");
            String sub = s.nextLine();

            if (sub.equals("1"))
            {
                System.out.println("Physics");

                int marks = 0;
                while (true)
                {
                    System.out.println("Enter marks  /Enter change for change  /Enter exit for leave");
                    if (s.hasNextInt())
                    {
                        marks = s.nextInt();
                        s.nextLine();
                    } else
                    {
                        String command = s.nextLine();
                        if (command.equalsIgnoreCase("exit")) break setSubject;
                        else if (command.equalsIgnoreCase("change")) continue setSubject;
                        else
                        {
                            System.out.println("Please enter a valid option");
                            continue;
                        }
                    }

                    if (marks < 40)
                    {
                        System.out.println("Student is fail");
                    } else if (marks == 40)
                    {
                        System.out.println("Student is fail he need more practice");
                    } else if (marks < 70)
                    {
                        System.out.println("need more practice but also good");
                    } else if (marks == 70)
                    {
                        System.out.println("Good");
                    } else if (marks < 90)
                    {
                        System.out.println("Good but also Excellent");
                    } else if (marks == 90)
                    {
                        System.out.println("Excellent");
                    } else if (marks < 100)
                    {
                        System.out.println("Outstanding");
                    } else if (marks == 100)
                    {
                        System.out.println("Good but also excellent");
                    } else
                    {
                        System.out.println("");
                    }
                }
            }
        }
    }

样品运行

Here is Subject list
1-Physics
2-Math
3-computer
Enter subject number here
1
Physics
Enter marks  /Enter change for change  /Enter exit for leave
change
Enter subject number here
1
Physics
Enter marks  /Enter change for change  /Enter exit for leave
50
need more practice but also good
Enter marks  /Enter change for change  /Enter exit for leave
60
need more practice but also good
Enter marks  /Enter change for change  /Enter exit for leave
exit

Process finished with exit code 0

通过一个while循环：

public static void main(String args[])
    {
        Scanner s = new Scanner(System.in);
        System.out.println("Here is Subject list");
        System.out.println("1-Physics");
        System.out.println("2-Math");
        System.out.println("3-computer");

        String subject = "";
        int marks = 0;

        while (true)
        {
            if (subject.isEmpty())
            {
                System.out.println("Enter subject number here");
                subject = s.nextLine();
            }

            if (subject.equals("1"))
            {
                System.out.println("Physics");

                System.out.println("Enter marks  /Enter change for change  /Enter exit for leave");
                if (s.hasNextInt())
                {
                    marks = s.nextInt();
                    s.nextLine();
                } else
                {
                    String command = s.nextLine();
                    if (command.equalsIgnoreCase("exit")) break ;
                    else if (command.equalsIgnoreCase("change")) {
                        subject = "";
                        continue ;
                    }
                    else
                    {
                        System.out.println("Please enter a valid option");
                        continue;
                    }
                }

                if (marks < 40)
                {
                    System.out.println("Student is fail");
                } else if (marks == 40)
                {
                    System.out.println("Student is fail he need more practice");
                } else if (marks < 70)
                {
                    System.out.println("need more practice but also good");
                } else if (marks == 70)
                {
                    System.out.println("Good");
                } else if (marks < 90)
                {
                    System.out.println("Good but also Excellent");
                } else if (marks == 90)
                {
                    System.out.println("Excellent");
                } else if (marks < 100)
                {
                    System.out.println("Outstanding");
                } else if (marks == 100)
                {
                    System.out.println("Good but also excellent");
                } else
                {
                    System.out.println("");
                }
                marks = 0;
            }
        }
    }

回答来源：Stack Overflow