Java connectivity issue with MySql database

Question

When I am trying retrieve values into a JTable it says "cast connectdb to connection", on the line con=Connect.ConnectDB(). But I have declared my Connect class without any error, and are able to insert values from another form successfully. This is my code:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
  try{
    con= Connect.ConnectDB();
    String sql="select * from pharmacy";
    pst = con.prepareStatement(sql);
    pst.execute();
    jTable1.setModel(DbUtils.resultSetToTableModel(rs));
    JOptionPane.showMessageDialog(this,"Succesfully stored","User",JOptionPane.INFORMATION_MESSAGE);

  } catch(SQLException ex){
    JOptionPane.showMessageDialog(this,ex);
  }
}

This is my Connect class:

public class Connect {
  Connection con=null;

  public static Connection ConnectDB(){
    try{

      Class.forName("com.mysql.jdbc.Driver");
      Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/hms_db1","root","root");
      return con;

    }catch(ClassNotFoundException | SQLException e){
      JOptionPane.showMessageDialog(null, e);
      return null;
    }      
  }
}

does db exist ??what is the line error occurred ?did you add mysql libry ? — Madhawa Priyashantha
– Madhawa Priyashantha, Commented Jan 6, 2015 at 6:25

Sharp Edge · Accepted Answer · 2015-01-06 07:16:27Z

2

jTable1.setModel(DbUtils.resultSetToTableModel(rs));

This is the line you're getting NullPointerException from.. because rs is null

change this line

pst.execute();

to

rs = pst.executeQuery();

You haven't assigned the result from the executeQuery() to the resultSet reference!! and since you're passing a null reference thats why you're getting a NPE. Hope this answers your question.

answered Jan 6, 2015 at 7:16

Sharp Edge

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qqilihq · Accepted Answer · 2015-01-06 06:59:28Z

0

try pst.executeQuery() in place of pst.execute()

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    try {
        con = Connect.ConnectDB();
        String sql = "select * from pharmacy";
        pst = con.prepareStatement(sql);
        pst.executeQuery();
        jTable1.setModel(DbUtils.resultSetToTableModel(rs));
        JOptionPane.showMessageDialog(this, "
            Succesfully stored" , "User", JOptionPane.INFORMATION_MESSAGE);
    } catch (SQLException ex) {
        JOptionPane.showMessageDialog(this, ex);
    }
}

edited Jan 6, 2015 at 6:59

qqilihq

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answered Jan 6, 2015 at 6:32

deval oza

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7 Comments

deval oza Over a year ago

jTable1.setModel(DbUtils.resultSetToTableModel(rs)); in this line where "rs" coming from?

Aboo Sidhu Over a year ago

ResultSet rs=null; under the class

deval oza Over a year ago

Have you try to store the result into "rs" like: ResultSet rs= pst.executeQuery(); ?

Aboo Sidhu Over a year ago

yes sir i have done,and now i can see the jtable values from the form which i inserted values,but i want to see the jtable and it's values in another form in the same package, and getting casting error in the line con="Connect.ConnectDB()";.

Aboo Sidhu Over a year ago

i have casted that line like " con= (Connection) Connect.ConnectDB();" and worked fine.

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