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POJava MySQL NullPointerException on query
 

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    <p>Basically I have a problem with getting a ResultSet from a database. The errors occur around Line 34 (?) in this code block but I've marked it</p> <pre><code>ResultSet rs = caq.executeQuery("SELECT * FROM ProjectScore"); //error goes here </code></pre> <p>I get a null pointer exception on runtime and this is the output from the catch statement below:</p> <pre><code>null, calculating average score failed java.lang.NullPointerException [Ljava.lang.StackTraceElement;@1de2b1 </code></pre> <p>The interesting thing is that I use the Connection Exactly the same in the class at the end and I receive no errors there. Copying the statement to the first class doesn't work either so I assume it's something else. I think that's all I have, any help is appreciated :)</p> <pre><code>import java.awt.*; import java.awt.event.*; import java.sql.*; import javax.swing.*; public class MainWindow extends JFrame implements ActionListener{ //....................... private int [] averageScore; //References private LogInWindow liw; private NewUserWindow nuw; private ScoreWindow sw; private boolean isAnotherWindowOpen = false; private boolean isLoggedIn = false; private ConnectionAndQueries caq; public MainWindow(ConnectionAndQueries caq) throws SQLException{ this.caq = caq; //................................. //Middle averageScore = new int [9]; calculateAverageScore(); setTable(); //............................ } private void calculateAverageScore() throws SQLException{ try{ ResultSet rs = caq.executeQuery("SELECT * FROM ProjectScore"); //error goes here int [] count = new int [9]; int [] totalScore = new int [9]; while(rs.next()){ int itemID = rs.getInt("itemID"); count[itemID]++; totalScore[itemID] += rs.getInt("Score"); } for(int i = 0; i &lt; 9; i++){ averageScore[i] = totalScore[i] / count[i]; } } catch (Exception e) { System.out.print(e.getMessage()); System.out.println(", calculating average score failed"); System.out.println(e.toString()); System.out.println(e.getStackTrace().toString()); } } } //next class import java.sql.*; public class ConnectionAndQueries { private static Connection connection; private static Statement statement; private MainWindow mw; public ConnectionAndQueries() throws ClassNotFoundException, SQLException{ mw = new MainWindow(this); connect(); } public static void connect() throws ClassNotFoundException, SQLException{ try{ Class.forName("com.mysql.jdbc.Driver"); connection = DriverManager.getConnection("jdbc:mysql://zzzzzzzzzz", "yyyy", "xxxx"); //dont think im allowed to give that info statement = connection.createStatement(); } catch (Exception e) { System.out.println("Connecting to the database failed"); } } public ResultSet executeQuery(String query) throws SQLException { return statement.executeQuery(query); } public int executeUpdate(String update) throws SQLException { return statement.executeUpdate(update); } public static void main(String [] args) throws ClassNotFoundException, SQLException{ ConnectionAndQueries caq = new ConnectionAndQueries(); } } //another class which uses the connection class, and works. import java.awt.*; import java.awt.event.*; import java.sql.*; import javax.swing.*; public class LogInWindow extends JFrame implements ActionListener{ //........................ //References private MainWindow mw; private ConnectionAndQueries caq; public LogInWindow(MainWindow mw, ConnectionAndQueries caq){ this.mw = mw; this.caq = caq; //...................... } public void actionPerformed(ActionEvent e) { if(e.getSource() == logIn){ String usn = usernameField.getText(); String pwd = passwordField.getText(); try { ResultSet rs = caq.executeQuery("SELECT * FROM ProjectCustomer"); while(rs.next()){ if(rs.getString("username").equals(usn)){ if(rs.getString("passwrd").equals(pwd)){ logInSuccess(usn); mw.userLoggedIn(usn); quit(); } } } if(mw.isUserLoggedIn() == false) logInFailed(); } catch (Exception e2) { System.out.print(e2.getMessage()); System.out.println(", error at log in"); System.out.println(e2.toString()); } } else if(e.getSource() == quit){ quit(); } } //............................ } </code></pre>
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