为什么选项的位置总是在变化？

Question

I'm doing a phone book project in Java, using MySql for school. I wanted to print the methods using the Class.getDeclaredMethods(); adding them to a Vector of type String . and invoke a menu() method that prints and accepts the option from the user using Scanner the problem is that it always changes the methods places. for example it can print 0.addPerson 1.deleteContact 2.searchByChar

and the next time 0.deleteContact 1.addPerson 2.searchByChar.

the problem is that i have a Switch case depend on it. the menu function:

public static int menu(Vector<?> options){
        System.out.println("The Options: ");
        for (int i = 0; i < options.size(); i++) {
            System.out.println(i + ". " + options.get(i));
        }
        Scanner scanner = new Scanner(System.in);
        System.out.println("Your Choice: ");
        String optionString = scanner.nextLine();
        int option = 0;
        if(isNumber(optionString)){
            option = Integer.valueOf(optionString);
        }else{
            System.out.println("Please Choose Valid Option");
            return menu(options);
        }
        return option;
    }

the methods that get my methods:

public static Vector<String> getClassMethods(Class whichClass){
        Method[] methods = whichClass.getDeclaredMethods();
        Vector<String> stringMethods = new Vector<>();
        for (Method method : methods) {
            if(Modifier.toString(method.getModifiers()).equals("protected")){
                stringMethods.add(method.getName());
            }
        }
        return stringMethods;
    }

my class the connects to the data base:

    private boolean getData(Person person){
    String sql = "SELECT * FROM " + DB_NAME + " WHERE name = '" + person.getName() + "' and phone_number = '" + person.getPhoneNumber() + "'";

    try {
        ResultSet resultSet = db.prepareStatement(sql).executeQuery();
        if (resultSet.next()) {
            return true;
        }
    } catch (SQLException e) {
        System.out.println(e.getMessage());
    }
    return false;
}

protected void addPerson(){
    Person person = MyUtills.createPerson();
    if(getData(person)){
        System.out.println(person.getName() + ", " + person.getPhoneNumber() + ": Already in Contacts" );
    }else{
        add(person);
    }
}

private void add(Person person) {
    String pName = person.getName();
    String pPhone = person.getPhoneNumber();
    String pAddress = person.getAddress();

    String sql = "INSERT INTO " + DB_NAME + " (name,phone_number,address)" +
                "VALUES (?,?,?)";

    try {
        statement = db.prepareStatement(sql);
        statement.setString(1,pName);
        statement.setString(2,pPhone);
        statement.setString(3,pAddress);
        statement.execute();
        System.out.println("Added Successfully");
    } catch (SQLException e) {
        e.printStackTrace();
    }
}

//delete contact by name
protected void deleteContact(){
    System.out.println("Enter Name Please");
    String name = MyUtills.readStringFromUser();
    Vector<Person> vector = checkMoreThanOne(name);
    if(vector.size() > 1){
        System.out.println("Choose One To Delete: ");
        int option = menu(vector);
        delete(vector.get(option));

    }
    System.out.println("Deleted");
}

private Vector<Person> checkMoreThanOne(String name) {
    Vector<Person> vector = new Vector<>();
    String sql = "SELECT * FROM " + DB_NAME;
    try {
        ResultSet resultSet = db.prepareStatement(sql).executeQuery();
        while(resultSet.next()){
            String pName = resultSet.getString("name");
            String pPhone = resultSet.getString("phone_number");
            String pAddress = resultSet.getString("address");
            if(pName.equals(name)){
                vector.add(new Person(pName,pPhone,pAddress));
            }
        }
        return vector;
    } catch (SQLException e) {
        e.printStackTrace();
    }
    return null;
}


//deleting and existing contact;
private void delete(Person person){
    String sql = "DELETE FROM " + DB_NAME + " WHERE name = '" + person.getName() + "' and phone_number = '" + person.getPhoneNumber() + "'";
    try {
        statement = db.prepareStatement(sql);
        statement.execute();
        System.out.println("Deleted Successfully");
    } catch (SQLException e) {
        e.printStackTrace();
    }
}


//creating a new table for empty data base!
private void createTable() {
    try {
        statement = db.prepareStatement(SQL_TABLE_STRING);
        statement.execute();
    } catch (SQLException e) {
        e.printStackTrace();
    }

}

protected void searchByFirstChar(Character character){
    Vector<Person> personVector = new Vector<>();
    String sql = "SELECT * FROM newphonebook";

    try {
        ResultSet resultSet = db.prepareStatement(sql).executeQuery();
        while(resultSet.next()){
            String name = resultSet.getString("name");
            String phoneNum = resultSet.getString("phone_number");
            String address = resultSet.getString("address");
            if(character.equals(name.charAt(0))){
                personVector.add(new Person(name,phoneNum,address));
            }
        }
        System.out.println(personVector);
    } catch (SQLException e) {
        System.out.println(e.getMessage());
    }
}

public void getOptions(){
    Vector<String> options = MyUtills.getClassMethods(DBWriterReader.class);
    int option = MyUtills.menu(options);
    switch (option){
        case 0:
            addPerson();
            break;
        case 1:
             deleteContact();
            break;
        case 2:
//                searchByFirstChar();
                break;
        }
    }

}

I know it's not best written but I'm working on it to make it better The Writing and Reading from the data base works fine, its the way it prints my methods that makes the problem..

Answer 1

If you need to guarantee the order of elements in a data structure, you don't use Vector -- it's not 1999 anymore. Look at the documentation for Vector . You get elements in the order determined by an iterator, not as they are stored.

Change your data structure to an ArrayList , which guarantees order. ArrayLists are also more performant in a single threaded application like yours, because unlike Vector, an ArrayList skips the overhead associated with being synchronized. Using the index of the ArrayList elements may also simplify the way you construct your switch statement.