JDBC MySql question

[santa]

Hi, im a newbeginner at JDBC and Mysql.
here is my problem:

public static void findUser(){
   
    try{
      
  
        card = Integer.parseInt(GUI.tmp);
        ResultSet RS = stmt.executeQuery
            ("SELECT name FROM borrowers WHERE cardnr = '"+ card + "'");

            while (RS.next()) {
                 System.out.print( RS.getString(1) );
               
             }

    }catch(Exception e) {
      System.err.println("Fail: " + e.getMessage());
      System.out.println("Fail: " + e);
      System.out.println("Card: " + card);
    }
}

All i want to do is check if the variable card is in cardnr column ... But i get nullpointerexception (card has a value) and database/Table exist...

Please someone help me =(

[Tolls]

What line is throwing the NullPointer?
In order to find that you need to change the catch block to e.printStackTrace().

[santa]

Database.findUser(Database.java:131)
GUI$4.actionPerformed(GUI.java:133)
javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
java.awt.Component.processMouseEvent(Component.java:6267)
javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
java.awt.Component.processEvent(Component.java:6032)
java.awt.Container.processEvent(Container.java:2041)
java.awt.Component.dispatchEventImpl(Component.java:4630)
java.awt.Container.dispatchEventImpl(Container.java:2099)
java.awt.Component.dispatchEvent(Component.java:4460)
java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
java.awt.Container.dispatchEventImpl(Container.java:2085)
java.awt.Window.dispatchEventImpl(Window.java:2478)
java.awt.Component.dispatchEvent(Component.java:4460)
java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

I'm only noob i cant read that =P cant see nullpointer =/

[Tolls]

Database.findUser(Database.java:131)

Line 131 of Database.java has the NullPointer.

So...which line is line 131?

[santa]

This was the line where

for (StackTraceElement ex : new Throwable().getStackTrace())
System.out.println(ex);

to print the stack trace =/

[santa]

obs my misstake

[santa]

The real printstacktrace shows a error at ResultSet RS = stmt.executeQuery line.

[goldest]

The real printstacktrace shows a error at ResultSet RS = stmt.executeQuery line.

So have you declared that "stmt" anywhere? You will need to use the Connection instance with createStatement().

Something like,

Statement stmt = Connection_Instance.createStatement();

Goldest

[Tolls]

So, as goldest says, stmt is null.
Without some more code we cannot tell you why it's null.

[santa]

import javax.swing.*;
import java.sql.*;

public class Database {
private static Statement stmt;
public static String database,allt3[] = new String[10];
public static int card;
private static boolean blank = false;

 public static void connectDatabase(){
 Statement stmt;
 Connection con = null;
 if(database.equals("")){
     JOptionPane.showMessageDialog(null, "Can't run without database!");
     System.exit(0);}

    try {
      Class.forName("com.mysql.jdbc.Driver").newInstance();
      con = DriverManager.getConnection("jdbc:mysql://",  // Using anonymous cause i feel like it =)
        "root", "test");


      if(!con.isClosed())
        System.out.println("Duude youre connected " +
          "trough TCP/IP...");

      stmt = con.createStatement();
      try{
      stmt.executeUpdate("USE " + database);
      System.out.println("Used old database!");
        }catch (Exception e){
           stmt.executeUpdate("CREATE DATABASE " + database);
           stmt.executeUpdate("USE " + database);
           System.out.println("Database created!");
        }
      stmt.executeUpdate ("CREATE TABLE Borrowers ("
              + "cardnr INT,"
              + "name CHAR(60), "
              + "street CHAR(40), "
              + "zip INT,"
              + "town CHAR(50))");

              stmt.executeUpdate ("CREATE TABLE GoodBooks ("
         + " ISBN long,"
        + " CopyNumber INT,"
        + " Title VARCHAR(60),"
        + " Author VARCHAR(30),"
        + " Publisher VARCHAR(50),"
        + " Year INT,"
        + " Statistics INT,"
        + " BorrowDate INT,"
        + " ReturnDate INT,"
        + " LibraryCardNumber INT)");
   for(int j = 0 ; j < Borrowers.borrow.length; j++){
                 stmt.executeUpdate("INSERT INTO Borrowers "
                         +"(cardnr, name, street, zip, town) "
                         + "VALUES "
                         + "('"+ Borrowers.borrow[j].LibraryCardNumber + "',"
                         + "'"+ Borrowers.borrow[j].Name + "',"
                         + "'"+ Borrowers.borrow[j].Street + "',"
                         + "'"+ Borrowers.borrow[j].ZipCode + "',"
                         + "'"+ Borrowers.borrow[j].Town + "')");
        }







for(int j = 0 ; j <Bookobjects.bookO.length ; j++){
                 stmt.executeUpdate("INSERT INTO goodbooks "
                         +"(ISBN, CopyNumber, Title, Author, Publisher, Year, Statistics,"
                         + " BorrowDate, ReturnDate, LibraryCardNumber) "
                         + "VALUES "
                         + "('"+ Bookobjects.bookO[j].ISBN + "',"
                         + "'"+ Bookobjects.bookO[j].CopyNumber + "',"
                         + "'"+ Bookobjects.bookO[j].Title + "',"
                         + "'"+ Bookobjects.bookO[j].Author + "',"
                         + "'"+ Bookobjects.bookO[j].Publisher + "',"
                         + "'"+ Bookobjects.bookO[j].Year + "',"
                         + "'"+ Bookobjects.bookO[j].Statistics + "',"
                         + "'"+ Bookobjects.bookO[j].BorrowDate + "',"
                         + "'"+ Bookobjects.bookO[j].ReturnDate + "',"
                         + "'"+ Bookobjects.bookO[j].LibraryCardNumber + "')");
        }
  




    } catch(Exception e) {
      System.err.println("Fail: " + e.getMessage());
      System.out.println("Fail: " + e);
    } /*finally {
      try {
        if(con != null)
           System.out.println("Connecton succesfully closed!");
          con.close();
      } catch(SQLException e) {}
    }*/


    }
public static void findUser(){
   
    try{
        if(GUI.tmp.equals("")){
            JOptionPane.showMessageDialog(null, "I don't accept blanks! Enter a number.");
         blank = true;
        }
      
     if(!blank){
        card = Integer.parseInt(GUI.tmp);
        ResultSet RS = stmt.executeQuery("SELECT name FROM borrowers WHERE cardnr = '"+ card + "'");

            while (RS.next()) {
                 System.out.print( RS.getString(1) );
               
             }
        }
    }catch(Exception e) {
      System.err.println("Fail: " + e.getMessage());
     e.printStackTrace();

     System.out.println("Card: " + card);
    }
    blank = false;
}
}

Here is the class ... any ideas?

[santa]

I forgot to remove "Statement stmt;".... THANK YOU GUYS =) I LOVE U ... The whole day spent on this mistake... and now im freee

[Tolls]

You beat me to it!
:)

[santa]

haha without you guys i would still be sitting changing the MySQL code and hoping for the best ... =D Thanks