Question

如果你们发现这个问题，请告诉我。我收到了这个错误：

Exception in thread "main" java.util.NoSuchElementException
    at java.util.Scanner.throwFor(Unknown Source)
    at java.util.Scanner.next(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at interaction.menu(interaction.java:15)
    at driver.main(driver.java:9)

第15行是selection = scan.nextInt();在while循环内部。 main只包含一个在此类中调用此方法的方法。

//provides the interface to be used
    public void menu(){
    Scanner scan = new Scanner(System.in);
    database db = new database();
    int selection;

    while(true){
        hugeTextBlock();
        selection = scan.nextInt();
        switch(selection){
            //creates a new course
            case 1: db.addCourse();
            //removes a course
            case 2: db.deleteCourse();
            //enroll a student
            case 3: db.enrollStudent();
            //delete a student
            case 4: db.deleteStudent();
            //register for a course
            case 5: db.registerStudent();
            //drop a course
            case 6: db.dropCourse();
            //check student registration
            case 7: db.checkReg();
            //quit
            case 8: break;  
            default: System.out.println("default action");
        }
    }
}

下面是另一个类中的addCourse方法。我自己运行它并且工作得很好。

//creates a new course
public void addCourse(){
    try{
    Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
    Connection conn = DriverManager.getConnection("jdbc:odbc:StudentRegistration_DSN");
    Statement st = conn.createStatement();
    Scanner scan = new Scanner(System.in);

    System.out.println("Please enter the course title: ");
    String title = scan.nextLine();
    System.out.println("Please enter the course's code: ");
    String code = scan.next();

    st.executeUpdate("insert into course values('"+code+"','"+title+"')");
    ResultSet rs = st.executeQuery("select * from course");
    code = "";
    title = "";
    System.out.println("This is the relation as of current changes.");

    while (rs.next())
    {
       code=rs.getString(1);
       title=rs.getString(2);
       System.out.println("Code: " + code + "   Title: " + title);
    }
    rs.close();
    st.close();
    conn.close();
    scan.close();
    }
    catch (Exception e){
        System.out.println(e);
    }

}

Answer 1

首先，只有打开案例8上的开关才会导致奇怪的事情发生。您应该在每个案例后添加一个中断，并为案例8添加System.exit(0)。

其次，您是否在扫描仪提示符处键入了任何内容？如果键入输入结束符号，则会发生这种情况。此外，System.in对应的流是什么？如果你从一个真正的命令行调用它并且不输入结束输入，我不知道这是怎么发生的。

Answer 2

异常告诉Scanner.nextInt没有要读取的int。您应确保扫描仪将返回的下一个事实上是一个int。请参阅Scanner.hasNextInt。

while (!scanner.hasNext()) {
    // sleep here
}
if (scanner.hasNextInt()) {
   selection = scan.nextInt();
} else {
    selection = 0;
    scan.next();  // reads the garbage.
}

简单的switch语句错误？

2 个答案: