private void add_computer_buttonActionPerformed(java.awt.event.ActionEvent evt) {                                                    
    // TODO add your handling code here:
    try{
    String url ="jdbc:derby://localhost:1527/Computer_Inventory";
    String usr ="admin1";
    String pass ="password";
    Connection con = DriverManager.getConnection(url,usr,pass); 
    Statement st = con.createStatement();
    String Query;
    Query = "INSERT INTO INVENTORY (EMP_NAME, DESIGNATION, ID, DEPARTMENT, COM_COMPANY, COM_MODEL, COM_SR_NO, COM_EXSER_TAG, PRIN_PRESENT, PRIN_COMPANY, PRIN_MODEL, PRIN_EXSER_TAG, PRIN_SR_NO, CARTRIDGE_MODEL, COMMISSION_DAY, COMMISSION_MONTH, COMMISSION_YEAR) VALUES ('"+emp_name_txt.getText()+"' , '"+designation_txt.getText()+"' , '"+emp_id_txt.getText()+"' , '"+emp_dept_txt.getText()+"' , '"+comp_company_txt.getText()+"' , '"+comp_model_txt.getText()+"' , '"+comp_serial_txt.getText()+"' , '"+comp_exsertag_txt.getText()+"' , '"+prin_present_combo.getSelectedItem()+"' , '"+prin_company_txt.getText()+"' , '"+prin_model_txt.getText()+"' , '"+prin_exsertag_txt.getText()+"' , '"prin_serial_txt.getText()"' , '"+prin_cartridge_txt.getText()+"' , '"+date_combo.getSelectedItem()+"' , '"+month_combo.getSelectedItem()+"' , '"+year_combo.getSelectedItem()+"')";
    JOptionPane.showMessageDialog(null, "Computer added to database");
    }
    catch(SQLException e){
       JOptionPane.showMessageDialog(null, e.toString());
    }
} 
it shows an error that a ; is mising (in "String Query = ..."). But i am not able to sort this out. please help. I am making this in netbeans.
Thanks a lot..!!
                        
As said in the comment by Sybren, you should use parameters for your query. Or you can also use String.format() to make this look better.
For the problem, search for
prin_serial_txt.getText()and do a proper concatination there in your Query string.