How do you make a String take the return value from a method?

Question

My program is like this: When I click a button, a popup will appear (a different JFrame class, I did not use JOptionPane) in that popup, there is a JTable which contains data from the database (which are file names) I want to take that file name and use it on a different class for use of another function.

Here I declared a String in "OpenLesson"(this is the popup) class:

public class openLesson extends javax.swing.JFrame {

    String activeLesson = "Manually Added"; //this is default when nothing is selected

    public openLesson() {
        initComponents();
    }

and then here is the getLesson() function that takes data from the database depending on what is selected on a JTable. And also change the value of the string activeLesson depending on what is selected:

public String getLesson() throws ClassNotFoundException, SQLException {

    int selectedColumn = 0;
    int selectedRow = tblOpenLesson.getSelectedRow(); // this is the JTable
    Connection con = null;
    Statement stmtGetLesson = null;
    try {
        Class.forName("org.sqlite.JDBC");
        con = DriverManager.getConnection("jdbc:sqlite:sql_items.sqlite");
        stmtGetLesson = con.createStatement();
        ResultSet rs = stmtGetLesson.executeQuery("SELECT * FROM lessons WHERE lesson = '" + tblOpenLesson.getModel().getValueAt(selectedRow, selectedColumn) + "';");

        if (rs.next()) {
            activeLesson = rs.getString("lesson"); // this (should) change the value of activeLesson above with the result of the query
            return rs.getString("lesson");
        }
    } catch (SQLException e) {
        JOptionPane.showMessageDialog(null, e);
    } catch (ClassNotFoundException ex) {
        Logger.getLogger(openLesson.class.getName()).log(Level.SEVERE, null, ex);
    } finally {
        con.close();
        stmtGetLesson.close();
    }
    return "";
}

Now, on a different class, I want to use the string activeLesson because I want to use it on an sqlite query for another JTable. Here's the function:

public void exeUpdateDBquestion_items(String ans, String desc) throws ClassNotFoundException, SQLException{
    openLesson ol = new openLesson();

    Connection con = null;
    Statement stmt = null;
    try {
        Class.forName("org.sqlite.JDBC");
        con = DriverManager.getConnection("jdbc:sqlite:sql_items.sqlite"); // connect to database
        stmt = con.createStatement();
        stmt.executeUpdate("INSERT INTO question_items (item_name, item_desc, lesson) VALUES ('" + ans + "','" + desc + "','" + ol.activeLesson + "')");
        JOptionPane.showMessageDialog(null, "Identified Item Saved!");
    } catch (SQLException e){
        JOptionPane.showMessageDialog(null, e.getMessage());
    } finally {
        con.close();
        stmt.close();
    }
}

And here comes the problem, no matter what I select on the JTable from the openLesson class, the activeLesson still uses the default text "Manually Added" and not the selected data.

I'm sorry if this is a dumb question, I'm new to java, and to Programming in general, so I'm not really understanding what is the problem here.

EDIT: This is how my Table is getting its data. When this button is clicked, the popup will appear containing the table (I have a function that updates the database before this function).

public void updateDBlessons() throws SQLException {
    Connection con = null;
    Statement stmt = null;
    try {
        Class.forName("org.sqlite.JDBC");
        con = DriverManager.getConnection("jdbc:sqlite:sql_items.sqlite");
        stmt = con.createStatement();
        ResultSet rs = stmt.executeQuery("SELECT * FROM lessons");
        DefaultTableModel dtm = (DefaultTableModel) tblOpenLesson.getModel();
        dtm.setRowCount(0);

        while(rs.next()){
            Object o[] = {rs.getString("lesson")};
            dtm.addRow(o);
        }
    } catch (ClassNotFoundException | SQLException e) {
        System.out.println(e);
    } finally {
        con.close();
        stmt.close();
    }
}

Are you certain `if (rs.next())` is evaluating to true? Maybe add a `System.out.print("reached");` in the if block — sleepToken, Mar 13 '20 at 12:40
We need to see your table code, not your loading code. If your table are displaying the correct information then the problem likely lies in your selectionlistener. — Ryan, Mar 13 '20 at 13:13
sleepToken, it did not evaluate to true, I've been looking at it for a while now and I can't seem to find why it does not work. I've editted the question to include how my Table gets its data. — itskenleton, Mar 13 '20 at 15:08

somar · Answer 1 · 2020-03-13T13:57:53.607

0

Considering that you instantiate a new object on your exeUpdateDBquestion_items() function, you have to call your getLesson() function if you want to change the value of the activeLesson attribute inside the other class.

public void exeUpdateDBquestion_items(String ans, String desc) throws ClassNotFoundException, SQLException{
openLesson ol = new openLesson();
ol.getLesson();

Or

public openLesson() {
    initComponents();
    this.getLesson();
}

And you can restrict access to your attribute and add getter/setter:

private String activeLesson

public getActiveLesson();
public setActiveLesson();

edited Mar 13 '20 at 13:57

answered Mar 13 '20 at 13:47

somar

36
5

Sorry but I'm not sure I'm understanding what you mean about "restrict access to your attribute and add getter/setter". What am I supposed to put in those function? – itskenleton Mar 13 '20 at 15:06
It is not really important but a good java programming practice, see : https://stackoverflow.com/questions/1568091/why-use-getters-and-setters-accessors – somar Mar 13 '20 at 15:44
public String getActiveLesson() { return this.activeLesson }; public void setActiveLesson(String activeLesson) { this.activeLesson = activeLesson }; – somar Mar 13 '20 at 15:51

score 0 · Accepted Answer · answered Mar 13 '20 at 16:40

I don't really know how I did it, but after 13 hours of experimenting, this worked for me.

I've made the function exeUpdateDBquestion_items take 3 parameters (this will now include the lesson) instead of explicitly putting it on the query:

public void exeUpdateDBquestion_items(String ans, String desc, String lesson) throws ClassNotFoundException, SQLException{

    Connection con = null;
    Statement stmt = null;
    try {
        Class.forName("org.sqlite.JDBC");
        con = DriverManager.getConnection("jdbc:sqlite:sql_items.sqlite"); // connect to database
        stmt = con.createStatement();
        stmt.executeUpdate("INSERT INTO question_items (item_name, item_desc, lesson) VALUES ('" + ans + "','" + desc + "','" + lesson + "')");
        JOptionPane.showMessageDialog(null, "Identified Item Saved!");
        System.out.println(ol.activeLesson + " lesson updated too");
    } catch (SQLException e){
        JOptionPane.showMessageDialog(null, e.getMessage());
    } finally {
        con.close();
        stmt.close();
    }
}

and in the button which activates this function, I called the method getLesson() instead of the String Variable activeLesson:

private void btnSaveIdentifiedActionPerformed(java.awt.event.ActionEvent evt) {                                                  
    btnIdentifyAnswer.setVisible(true);
    btnIdentifyDesc.setVisible(false);
    btnSaveIdentified.setVisible(false);
    openLesson ol = new openLesson(); // this is the other class

    try {
        if (checkIfExists() == true){
            JOptionPane.showMessageDialog(null, "Item Already Exists.");
        } else {
        exeUpdateDBquestion_items(ansTempHandler, descTempHandler, ol.getLesson()); // called the method here instead of the variable
        }
    } catch (ClassNotFoundException | SQLException ex) {
        Logger.getLogger(mainScreen.class.getName()).log(Level.SEVERE, null, ex);
    }
}

and this solved the problem. Thank you guys for all the hints.

How do you make a String take the return value from a method?

2 Answers2