How do i fix a NullPointerException while calling my GUI

Question

My exception is in the line where i call my GUI: XmasGUI tableGUI = new XmasGUI (xmasDataModel); My other exception is in the line where i set my content panel to (rootPanel) in my XmasGUI.java code. I'm not understanding what could be null. Can someone point me in the right direction? Seems like i'm going to get flagged our down voted. It seems my questions are always (too vague) but to me they are quite simple and to the point.

import java.sql.*;

public class XmasDB {
    static final String DB_CONNECTION_URL = "jdbc:mysql://localhost:3306/";
    static final String USER = "root";   //TODO replace with your username
    static final String PASS = "****";   //TODO replace with your password
    static private final String DB_NAME = "xmas";


    public final static String WANT_TABLE_NAME = "want_list";
    public final static String NEED_TABLE_NAME = "need_list";
    // Each solver will have a unique ID
    public final static String PK_COLUMN = "id";
    // A primary key is needed to allow updates to the database on modifications to ResultSet
    public final static String NAME_COLUMN = "name";
    public final static String PRICE_COLUMN = "price";
    public final static String PRIORITY_COLUMN = "riority";

    public final static int MOVIE_MIN_RATING = 1;
    public final static int MOVIE_MAX_RATING = 5;



    // Name our database

    static Statement statement = null;
    static Connection conn = null;
    static ResultSet rs = null;
    // Create out data model
    private static XmasDataModel xmasDataModel;

    public static void main(String args[]) {


        //setup creates database (if it doesn't exist), opens connection, and adds sample data

        if (!setup()) {
            System.exit(-1);
        }

        if (!loadAllMovies()) {
            System.exit(-1);
        }

        //If no errors, then start GUI
        XmasGUI tableGUI = new XmasGUI (xmasDataModel);

    }

    //Create or recreate a ResultSet containing the whole database, and give it to movieDataModel
    public static boolean loadAllMovies(){

        try{

            if (rs!=null) {
                rs.close();
            }

            String getSomeData = "SELECT * FROM " + WANT_TABLE_NAME;
            String getRestData = "SELECT * FROM " + NEED_TABLE_NAME;

            rs = statement.executeQuery (getSomeData);
            rs = statement.executeQuery (getRestData);


            if (xmasDataModel == null) {
                //If no current movieDataModel, then make one
                xmasDataModel = new XmasDataModel (rs);
            } else {
                //Or, if one already exists, update its ResultSet
                xmasDataModel.updateResultSet(rs);
            }

            return true;

        } catch (Exception e) {
            System.out.println("Error loading or reloading lists");
            System.out.println(e);
            e.printStackTrace();
            return false;
        }

    }

    public static boolean setup(){
        try {

            //Load driver class
            try {
                String Driver = "com.mysql.jdbc.Driver";
                Class.forName(Driver);
            } catch (ClassNotFoundException cnfe) {
                System.out.println("No database drivers found. Quitting");
                return false;
            }

            conn = DriverManager.getConnection(DB_CONNECTION_URL + DB_NAME, USER, PASS);

            statement = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);

            //Does the table exist? If not, create it.
            if (! xmasTableOneExists ()) {

                //Create a table
                String createNeedTableSQL = "CREATE TABLE " + NEED_TABLE_NAME + " (" + PK_COLUMN + " int NOT NULL AUTO_INCREMENT, " + NAME_COLUMN + " varchar(50), " + PRICE_COLUMN + " int, " + PRIORITY_COLUMN + " int, PRIMARY KEY(" + PK_COLUMN + "))";
                System.out.println ( createNeedTableSQL );


                statement.executeUpdate ( createNeedTableSQL );

                System.out.println ( "Created Need table..." );

                String addDataSQL = "INSERT INTO " + NEED_TABLE_NAME + "(" + NAME_COLUMN + ", " + PRICE_COLUMN + ", " + PRIORITY_COLUMN + ")" + " VALUES ('New Winter Boots', 85, 3)";
                statement.executeUpdate ( addDataSQL );
                addDataSQL = "INSERT INTO " + NEED_TABLE_NAME + "(" + NAME_COLUMN + ", " + PRICE_COLUMN + ", " + PRIORITY_COLUMN + ")" + " VALUES('New Car', 3000, 2)";
                statement.executeUpdate ( addDataSQL );
                addDataSQL = "INSERT INTO " + NEED_TABLE_NAME + "(" + NAME_COLUMN + ", " + PRICE_COLUMN + ", " + PRIORITY_COLUMN + ")" + " VALUES ('Gift Card to Grocery Store', 300, 1)";
                statement.executeUpdate ( addDataSQL );

            }else if (! xmasTableTwoExists ()) {
                String createWantTableSQL = "CREATE TABLE " + WANT_TABLE_NAME + " (" + PK_COLUMN + " int NOT NULL AUTO_INCREMENT, " + NAME_COLUMN + " varchar(50), " + PRICE_COLUMN + " int, " + PRIORITY_COLUMN + " int, PRIMARY KEY(" + PK_COLUMN + "))";
                System.out.println (createWantTableSQL);
                statement.executeUpdate(createWantTableSQL);
                System.out.println("Created Want Table...");

                String addMoreSQL = "INSERT INTO " + WANT_TABLE_NAME + "(" + NAME_COLUMN + ", " + PRICE_COLUMN + ", " + PRIORITY_COLUMN + ")" + " VALUES ('Gaming PC', 500, 3)";
                statement.executeUpdate(addMoreSQL);
                addMoreSQL = "INSERT INTO " + WANT_TABLE_NAME +  "(" + NAME_COLUMN + ", " + PRICE_COLUMN + ", " + PRIORITY_COLUMN + ")" + " VALUES('Astrology Book', 150, 2)";
                statement.executeUpdate(addMoreSQL);
                addMoreSQL = "INSERT INTO " + WANT_TABLE_NAME +  "(" + NAME_COLUMN + ", " + PRICE_COLUMN + ", " + PRIORITY_COLUMN + ")" + " VALUES ('Hover Board', 300, 1)";
                statement.executeUpdate(addMoreSQL);
            }
            return true;

        } catch (SQLException se) {
            System.out.println(se);
            se.printStackTrace();
            return false;
        }
    }

    private static boolean xmasTableOneExists () throws SQLException {

        String checkNeedTablePresentQuery = "SHOW TABLES LIKE '" + NEED_TABLE_NAME + "'";   //Can query the database schema
        ResultSet tablesRS = statement.executeQuery(checkNeedTablePresentQuery);

        if (tablesRS.next()) {    //If ResultSet has a next row, it has at least one row... that must be our table
            return true;
        }
        return false;

    }
    private static boolean xmasTableTwoExists () throws SQLException {

        String checkWantTablePresentQuery = "SHOW TABLES LIKE '" + WANT_TABLE_NAME + "'";

        ResultSet tableTwoRS = statement.executeQuery(checkWantTablePresentQuery);

        if (tableTwoRS.next()) {    //If ResultSet has a next row, it has at least one row... that must be our table
            return true;
        }
        return false;

    }

    //Close the ResultSet, statement and connection, in that order.
    public static void shutdown(){
        try {
            if (rs != null) {
                rs.close();
                System.out.println("Result set closed");
            }
        } catch (SQLException se) {
            se.printStackTrace();
        }

        try {
            if (statement != null) {
                statement.close();
                System.out.println("Statement closed");
            }
        } catch (SQLException se){
            //Closing the connection could throw an exception too
            se.printStackTrace();
        }

        try {
            if (conn != null) {
                conn.close();
                System.out.println("Database connection closed");
            }
        }
        catch (SQLException se) {
            se.printStackTrace();
        }
    }
}

//(This is my XmasGUI.java Class)
/


import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import java.util.Calendar;

/**
 * Created by Nnamdi on 11/29/2016.
 */
public class XmasGUI extends JFrame implements WindowListener{
    private JTable needTable;
    private JTextPane NEEDTABLETextPane1;
    private JTextPane WANTTABLETextPane;
    private JTable wantTable;
    private JButton addButton;
    private JButton exitButton;
    private JTextPane welcomeToXmasListTextPane;
    private JButton transferButton;
    private JRadioButton radioNeed;
    private JRadioButton radioWant;
    private JTextField txtNameInput;
    private JSpinner prioritySpinner;
    private JTextField txtPriceInput;
    private JPanel rootPanel;
    private JButton deleteButton;

    XmasGUI(final XmasDataModel xmasDataTableModel) {

        setContentPane(rootPanel);
        pack();
        setTitle("Christmas List Database Application");
        addWindowListener(this);
        setVisible(true);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);


        //Set up JTables
        needTable.setGridColor(Color.BLACK);
        needTable.setModel(xmasDataTableModel);
        wantTable.setGridColor (Color.YELLOW);
        wantTable.setModel (xmasDataTableModel );

        //Set up the priority spinner.
        //SpinnerNumberModel constructor arguments: spinner's initial value, min, max, step.
        prioritySpinner.setModel(new SpinnerNumberModel(1, XmasDB.MOVIE_MIN_RATING, XmasDB.MOVIE_MAX_RATING, 1));

        exitButton.addActionListener ( new ActionListener ( ) {
            @Override
            public void actionPerformed ( ActionEvent e ) {
            XmasDB.shutdown();
            System.exit (0);
            }
        } );
        deleteButton.addActionListener ( new ActionListener ( ) {
            @Override
            public void actionPerformed ( ActionEvent e ) {
                int currentRow = needTable.getSelectedRow();
                int currentrow = wantTable.getSelectedRow();

                if (currentRow == -1) {      // -1 means no row is selected. Display error message.
                    JOptionPane.showMessageDialog(rootPane, "Please choose a item to delete");
                }
                boolean deleted = xmasDataTableModel.deleteRow(currentRow);
                if (deleted) {
                    XmasDB.loadAllMovies();
                } else {
                    JOptionPane.showMessageDialog(rootPane, "Error deleting item");
                }
            }
        } );
    }


    @Override
    public void windowOpened ( WindowEvent e ) {

    }

    @Override
    public void windowClosing ( WindowEvent e ) {
        System.out.println("closing");
        XmasDB.shutdown();
    }

    @Override
    public void windowClosed ( WindowEvent e ) {

    }

    @Override
    public void windowIconified ( WindowEvent e ) {

    }

    @Override
    public void windowDeiconified ( WindowEvent e ) {

    }

    @Override
    public void windowActivated ( WindowEvent e ) {

    }

    @Override
    public void windowDeactivated ( WindowEvent e ) {

    }

    private void createUIComponents () {
        // TODO: place custom component creation code here
    }
}

You don't initialize any of your fields / members in the xmas ui class. — meistermeier, Dec 05 '16 at 20:40

score 1 · Answer 1 · answered Dec 05 '16 at 20:50

Please, first, ensure that you've imported XmasGUI class before using it:
As an example: import com.mypackage.XmasGUI; in class XmasDB.

Second, setContentPane(rootPanel); is misspelt. It should be setContentPanel(rootPanel);

Third, you need to ensure the value of rootPanel isn't null when passing it to setContentPanel();
You can initialize it before passing it to setContentPanel();.

How do i fix a NullPointerException while calling my GUI

1 Answers1