Thread: Aggravating project, need fresh eyes and help

I'm in a Java programming course in college. For some reason, for a noncertified course, they want us to do this big project that includes building a student records management... thing. I think I have it ... mostly... done. Except the one class that's meant to drive the whole thing is driving me up the wall. There are a number of issues, but... yes. I need someone to take a look and help me figure out how to fix the problem so it will at least work.

private void updateStudent() {
    System.out.print("Choose the type:\n1=Undergraduate 2=Graduate 3=PartTime: ");
        int type = 0;
        StudentRecords st;
        do {
            while (!scan.hasNextInt()) {
                scan.next();
            }
            type = scan.nextInt();
            scan.nextLine();
        } while (type < 0 || type > 3);
      if (type == 1) {
            st = new Undergraduate();
        } else if (type == 2) {
            st = new Graduate();
        } else {
            st = new PartTime();
        }
        System.out.print("Enter the stduentID: ");
        while (!scan.hasNextInt()) {
            scan.next();
        }
        int id = scan.nextInt();
        scan.nextLine();
        st.setStudentID(id);
        readStudent(st);
        st.update ();
    }

it's the middle part, where it talks about st = new Undergraduate(); that my Netbeans keeps flagging and not liking. If you want to see the whole project let me know.

What exactly the error is?

Hi, in the code snippet above, the if/else sequence where "st = new Undergraduate();" is listed, each one comes up red in Netbeans. Alt-entering gets the following message: "constructor Undergraduate cannot be applied to given types; required: String, String, int, double, String, String, String found: no arguments reason: actual and formal argument lists differ in length" and then alt enter suggests creating constructor Undergraduate() in student.Undergraduate.

I realize it's a bit complicated. I have the project exported, but don't know where to post it so others could see it.

Check, what constructors does Undergraduate have and what does not.

Please post the code in question on the forum, and not through some link.

It was a pastebin link... it was the code. But fine... think query is okay now but need to go to delete. It needs to just delete a user-specified student ID rather than asking first for graduate-undergraduate-parttime. I realize this is just a code snippet, but the entire project spans six class files and posting all of them would just be too long... and I can't link to pastebin either so. Just need to figure out how to rewrite it to accept user input of studentid and either delete or update. query by id update maybe too.

private void deleteStudent() {
        System.out.print("Choose the type:\n1- Undergraduate, 2- Graduate, 3- Part-Time: ");
        int type = 0;
        Student st;
        do {
            while (!scan.hasNextInt()) {
                scan.next();
            }
            type = scan.nextInt();
            scan.nextLine();
        } while (type < 0 || type > 3);
        if (type == 1) {
            st = new Undergraduate();
        } else if (type == 2) {
            st = new Graduate();
        } else {
            st = new PartTime();
        }
        System.out.print("Please enter the student ID: ");
        while (!scan.hasNextInt()) {
            scan.next();
        }
        int id = scan.nextInt();
        scan.nextLine();
        st.setStudentID(id);
        st.delete();
    }

Originally Posted by sevenday

Just need to figure out how to rewrite it to accept user input of studentid and either delete or update. query by id update maybe too.

When you refer to updating or deleting content, do you mean that you want the program to write (and later read) from an external file, where each student ID is on a separate line or separated by a delimiter?

Originally Posted by sevenday

It needs to just delete a user-specified student ID rather than asking first for graduate-undergraduate-parttime.

When the user enters 1, 2 or 3, a new object is created. In doing so, I'm guessing a student ID set for each object automatically. If that's the case, then you want the program to delete a student ID right away, however, this can be problematic if you're not writing to an external file and the program has just be ran as there will be no data to delete. Before deleting, you should have some way of checking to make sure there is at least 1 set student ID.

I'm a bit confused, do you want the program to delete a student ID before asking the user to enter 1, 2 or 3? If so, why not just move that segment of code, or am I misunderstanding what you're asking?

Also, the last 2 lines of code are a bit unusual, however, it may be due to only seeing a code snippet. Are you setting the student ID to whatever the user entered, then deleting it right away? If so, setting it is an unnecessary step. I may be wrong in this though since I cannot see the code for those methods.

Originally Posted by sevenday

It was a pastebin link... it was the code. But fine...

We ask that you post all relevant materials on the forum because we have no way to guarantee a third party will continue to host your content for the thread. This way the content is under control of this forum. Thank you for your cooperation.

If you are having trouble writing code to accept user input, I suggest starting with a small program (like a hello world example) and adapt it to print what the user types instead of "Hello world". Post the code if you have any questions.

Originally Posted by jps

a small program (like a hello world example) and adapt it to print what the user types instead of "Hello world".

That's not the problem for me. I'm just having trouble picking out how to take user input (in this case an integer, studentID) and using that to select a database row and delete it. I know this part: SELECT * FROM student WHERE= .... and there it stops, because I've tried + getstudentID and that doesn't work.

Regarding the question about external file: Yes, there is an external registrar.sql file that is accessed to add, update, delete, etc. It has to persist. Student ID is not automatically assigned, it is given by the user. When a student is added, the program asks for a student ID. if I type in 55, I need to be able to call up that entry for student ID 55 without needing to ask whether the student is an undergraduate, graduate, or part time (the 1 - 2 - 3 if/else sequence currently existing). The query is working for now. It's the update/delete sections that I'm wrestling with now.

I realize that the solution is likely very simple and I'm just not seeing it.

Edit to add: I know that you need to see the whole code to understand it and explain it but if I tried to paste all six class files here it would be a hugely long post. I don't know else to get around that and still adhere to the no-link rule. I'm sorry.

Originally Posted by sevenday

That's not the problem for me. I'm just having trouble picking out how to take user input (in this case an integer, studentID) and using that to select a database row and delete it.

This describes multiple things. Which one specific thing are you stuck on? Reading input? Selecting a row? Deleting the row? Updating the display?

Originally Posted by sevenday

I know this part: SELECT * FROM student WHERE= ....

I do not understand what that means

Originally Posted by sevenday

I've tried + getstudentID and that doesn't work.

Post the code where you tried that. It is hard to say what might have gone wrong without seeing it.

Originally Posted by sevenday

I know that you need to see the whole code to understand

No, not really.

Originally Posted by sevenday

if I tried to paste all six class files here it would be a hugely long post. I don't know else to get around that and still adhere to the no-link rule. I'm sorry.

This is why I said to adapt a "Hello world" program. They are short and easy to understand. Once you have the concept, you can apply it to your project. See SSCCE.org

I know how to get user input and add it to a database or print it back out to the user. The problem is how to pick ONE entry out of a database, based on user input, and delete or update it. I need to be able to type in any student ID (that exists) and update or delete it. Edit: Without needing to know what category it's in first! Right now it uses an if/else set to select from categories, but I don't need to do that.

This is the code for the application driver class.

package teststudent;
 
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Scanner;
 
public class StudentApp{
 
    private Scanner scan = new Scanner(System.in);
 
    public static void main(String[] args) {
        new StudentApp().displayMenu();
    }
 
    //Creates SMS menu
    private void displayMenu() {
        System.out.println("Student Management System");
        int menu;
 
        while ((menu = getOption()) != 6) {
            switch (menu) {
                case 1:
                    addStudent();
                    break;
                case 2:
                    updateStudent();
                    break;
                case 3:
                    deleteStudent();
                    break;
                case 4:
                    queryStudent();
                    break;
                case 5:
                    calculateTuition();
                    break;
                default:
                    System.out.println("Please select an option between 1 and 6.");
                    break;
            }
            System.out.print("\nPlease press enter to continue.");
            scan.nextLine();
        }
        System.out.println("\nThank you for using the system.");
    }
 
    private int getOption() {
        System.out.println();
        System.out.println("1. Add Student");
        System.out.println("2. Update Student");
        System.out.println("3. Delete Student");
        System.out.println("4. Query Student");
        System.out.println("5. Calculate Tuition");
        System.out.println("6. Exit");
        System.out.print("Enter your choice (1-6): ");
        while (!scan.hasNextInt()) {
            scan.next();
        }
        int opt = scan.nextInt();
        scan.nextLine();
        return opt;
    }
 
    //Adds a student
    private void addStudent() {
        System.out.print("Please enter the student ID: ");
        while (!scan.hasNextInt()) {
            scan.next();
        }
        int id = scan.nextInt();
        scan.nextLine();
        System.out.print("Choose the type of student:\n1- Undergraduate, 2- Graduate, 3- Part-Time: ");
        int type = 0;
        Student st;
        do {
            while (!scan.hasNextInt()) {
                scan.next();
            }
            type = scan.nextInt();
            scan.nextLine();
        } while (type < 0 || type > 3);
        if (type == 1) {
            st = new Undergraduate();
        } else if (type == 2) {
            st = new Graduate();
        } else {
            st = new PartTime();
        }
        st.setStudentID(id);
        st.setStudentID(id);
        readStudent(st);
        st.add();
    }
 
    //Reads student information from user
    private void readStudent(Student st) {
        System.out.print("Please enter student's first name: ");
        st.setFirstName(scan.next());
        scan.nextLine(); // skip
        System.out.print("Please enter student's last name: ");
        st.setLastName(scan.next());
        scan.nextLine();
        System.out.print("Please enter student's GPA: ");
        while (!scan.hasNextDouble()) {
            scan.next();
        }
        st.setGPA(scan.nextDouble());
        scan.nextLine();
        System.out.print("Choose the student's status(1- Resident, 2- Non-Resident): ");
        while (!scan.hasNextInt()) {
            scan.next();
        }
        if (scan.nextInt() == 1) {
            st.setStatus("Resident");
        } else {
            st.setStatus("Non-Resident");
        }
        scan.nextLine();
 
        if (st instanceof Graduate) {
            Graduate gst = (Graduate) st;
            System.out.print("Please enter the thesis title: ");
            gst.setThesisTitle(scan.nextLine());
            System.out.print("Please enter the thesis advisor: ");
            gst.setThesisAdvisor(scan.nextLine());
        } else if (st instanceof Undergraduate) {
            Undergraduate ust = (Undergraduate) st;
            System.out.print("Please choose the student's level:\n1- Freshman, 2- Sophomore, 3- Junior, 4- Senior: ");
            int id = 0;
            do {
                while (!scan.hasNextInt()) {
                    scan.next();
                }
                id = scan.nextInt();
                scan.nextLine();
            } while (id < 0 || id > 4);
            if (id == 1) {
                ust.setLevel("Freshman");
            } else if (id == 2) {
                ust.setLevel("Sophomore");
            } else if (id == 3) {
                ust.setLevel("Junior");
            } else if (id == 4) {
                ust.setLevel("Senior");
            }
        } else if (st instanceof PartTime) {
            PartTime pst = (PartTime) st;
            System.out.print("Please enter the name of the company: ");
            pst.setCompany(scan.nextLine());
        }
    }
 
    //Update a student record
    private void updateStudent() {
        System.out.print("Choose the type:\n1- Undergraduate, 2- Graduate, 3- Part-Time: ");
        int type = 0;
        Student st;
        do {
            while (!scan.hasNextInt()) {
                scan.next();
            }
            type = scan.nextInt();
            scan.nextLine();
        } while (type < 0 || type > 3);
        if (type == 1) {
            st = new Undergraduate();
        } else if (type == 2) {
            st = new Graduate();
        } else {
            st = new PartTime();
        }
        System.out.print("Please enter the student ID: ");
        while (!scan.hasNextInt()) {
            scan.next();
        }
        int id = scan.nextInt();
        scan.nextLine();
        st.setStudentID(id);
        readStudent(st);
        st.update();
    }
 
    //Deletes a student record
    private void deleteStudent() {
        System.out.print("Choose the type:\n1- Undergraduate, 2- Graduate, 3- Part-Time: ");
        int type = 0;
        Student st;
        do {
            while (!scan.hasNextInt()) {
                scan.next();
            }
            type = scan.nextInt();
            scan.nextLine();
        } while (type < 0 || type > 3);
        if (type == 1) {
            st = new Undergraduate();
        } else if (type == 2) {
            st = new Graduate();
        } else {
            st = new PartTime();
        }
        System.out.print("Please enter the student ID: ");
        while (!scan.hasNextInt()) {
            scan.next();
        }
        int id = scan.nextInt();
        scan.nextLine();
        st.setStudentID(id);
        st.delete();
    }
 
    //Queries for a student record
    private void queryStudent() {
        Connect gc = new Connect();
        Statement stmt = null;
        Connection conn = gc.getSimpleConnection();
        try {
            stmt = conn.createStatement();
            String select = "SELECT * FROM student";
            ResultSet rs = stmt.executeQuery(select);
            System.out.println("Student Records:");
            while (rs.next()) {
                System.out.println("Student ID#:\t" + rs.getString("studentID"));
                System.out.println("First Name:\t" + rs.getString("firstName"));
                System.out.println("Last Name:\t" + rs.getString("lastName"));
                System.out.println("Grade Average(GPA):\t" + rs.getString("gpa"));
                System.out.println("Status:\t" + rs.getString("status"));
                System.out.println("Mentor name:\t" + rs.getString("mentor"));
                System.out.println("Level:\t" + rs.getString("level"));
                System.out.println("Thesis title:\t" + rs.getString("thesisTitle"));
                System.out.println("Thesis advisor:\t" + rs.getString("thesisAdvisor"));
                System.out.println("Company:\t" + rs.getString("company"));
                System.out.println("\n");
            }
            stmt.close();
            conn.close();
        } catch (SQLException e) {
            System.out.println(e.getMessage());
        }
    }
 
    //Calcuate's student tuition
    private void calculateTuition() {
        System.out.print("Choose the type:\n1- Undergraduate, 2- Graduate, 3- Part-Time: ");
        int type = 0;
        Student st;
        do {
            while (!scan.hasNextInt()) {
                scan.next();
            }
            type = scan.nextInt();
            scan.nextLine();
        } while (type < 0 || type > 3);
        if (type == 1) {
            st = new Undergraduate();
        } else if (type == 2) {
            st = new Graduate();
        } else {
            st = new PartTime();
        }
 
        System.out.print("Please enter the student's hours: ");
        while (!scan.hasNextInt()) {
            scan.next();
        }
        int hours = scan.nextInt();
        scan.nextLine();
 
        System.out.print("Choose the student's status(1- Resident, 2- Non-Resident): ");
        while (!scan.hasNextInt()) {
            scan.next();
        }
        int status = scan.nextInt();
        scan.nextLine();
 
        double value = st.calculateTuition(hours, status);
        System.out.printf("The tuition is %.2f\n", value);
    }
}

Originally Posted by sevenday

I know how to get user input and add it to a database or print it back out to the user. The problem is how to pick ONE entry out of a database

Work on this part first.
How do you get an element from the database to print it to the user? Short of writing the code for you I do not know how to better answer the question.

--- Update ---

Perhaps you can describe in more detail what you are having problems with specifically? What line of code do you get to? ...as in the line that searches the database or the line of code that returns the found element

Originally Posted by sevenday

That's not the problem for me. I'm just having trouble picking out how to take user input (in this case an integer, studentID) and using that to select a database row and delete it. I know this part: SELECT * FROM student WHERE= .... and there it stops, because I've tried + getstudentID and that doesn't work.

Are there any errors that appear? There are a few problems I see. First, in your statement, you're only specifying a table name but not the database where that table can be found. Instead, try SELECT * FROM databaseName.tableName. Second, try using PreparedStatements when manipulating data in the database as they are better at handling variables. Basically, the Statement is kept to access the database and table, while the prepared statements will do all the hard work.

Here is a link to the documentation for prepared statements: PreparedStatement (Java Platform SE 6)

Third, whenever you're writing/reading to external files or a SQL database, you should place the .close() methods in a finally block so it will always be executed no matter if the code will enter the catch. For example:

try {
// code that will be run
} catch (Exception ex) {
// something that will happen if there is an Exception error
} finally {
resultSet.close();
statement.close();
connection.close();
// if you want to be thorough, you can check to see whether each is not null then close.
}

Originally Posted by sevenday

Regarding the question about external file: Yes, there is an external registrar.sql file that is accessed to add, update, delete, etc. It has to persist. Student ID is not automatically assigned, it is given by the user. When a student is added, the program asks for a student ID. if I type in 55, I need to be able to call up that entry for student ID 55 without needing to ask whether the student is an undergraduate, graduate, or part time (the 1 - 2 - 3 if/else sequence currently existing). The query is working for now. It's the update/delete sections that I'm wrestling with now.

Before figuring out the code for updating, you need to make the resultSet updatable because by default, they are not. Happily, the Java documentation shows not only how to do this but also samples of how to update in just a few lines. ResultSet (Java Platform SE 6)

The update code block, as it is, runs without errors and updates as intended. The finally block - I see your point on that one, edited those in.

Our coursework didn't cover prepared statements, and I'm... frankly, a little too overwhelmed right now. Resultset - got that, editing that in, too.

On looking at it, I'm wondering if I need to do too much more to it. The problem with the updating is that the three types (graduate, undergrad, parttime) all have different sets of information that need to be updated. All of them have the basic set (firstname, lastname, gpa, mentor, studentid) but graduate adds in (thesistitle, thesisadvisor) and parttime adds (company). I can't think of a way to properly update without using the current system. The other student I spoke to used a similar setup and his project passed, so I think I might throw it to the reviewers and see if they will take it.

And of course I run into more issues.

private void deleteStudent(){
	Connect gc = new Connect();
        Statement stmt = null;
        Connection conn = gc.getSimpleConnection();
        try
        {
            stmt = conn.createStatement();
            System.out.println("Enter Student ID:");
            while (!scan.hasNextInt()) {
            scan.next();
            }
            int id = scan.nextInt();
            scan.nextLine();
            stmt.execute("Delete FROM student WHERE studentID=" + "'" + id + "'");
 
            stmt.close();
            conn.close();
        }
         catch (SQLException e)
         {
            e.printStackTrace();
            System.err.println("Could not delete student");
 
         }
        System.out.println("Successfully deleted student from the database");
    }

This is my current delete student code block. When I try to move the conn.close(); etc outside into a finally block, it red-lines it and wants to surround it by a try/catch block or add a "throws SQL" to the constructor. But when I do THAT, the case set up top doesn't like it because deleteStudent(); no longer matches. God, what a headache.