finishing up a DB/Java exercise

[hayden06f4i]

so i feel like im almost there, just not understanding the final steps, could someone let me know what i need to do to finish this program up? also as a side note, how do i post my code here WITH line numbers to make it easy for you guys?

this program primarily i worked from the
private void stockInfoJButtonActionPerformed( ActionEvent event ) line onward, and im having trouble understand what i need to do to get it finished up. i think im ok up until the "computetotalvalue method, but im starting to not understand exactly what i should be doing in that method. right now when i compile i get a "missing return statement", but there are probably additional issues as well. the DB is called "stockInformation" and contains stockName, stockSymbol, shares, and price fields, i am trying to access those, and also show an additional field in the java program that calculates the # of shares times the price and displays the total.....

// Exercise 26.11: StockPortfolio.java
// Displays a client's stock portfolio.
import java.awt.*;
import java.awt.event.*;
import java.sql.*;
import java.text.*;
import javax.swing.*;

public class StockPortfolio extends JFrame
{
   // JLabels for prompt
   private JLabel prompt1JLabel;
   private JLabel prompt2JLabel; 

   // JComboBox for stock names
   private JComboBox stockNamesJComboBox;

   // JButton for stock information
   private JButton stockInfoJButton;

   // JPanel for displaying stock information
   private JPanel stockInfoJPanel;

   // JLabel and JTextField for stock name
   private JLabel stockNameJLabel; 
   private JTextField stockNameJTextField;

   // JLabel and JTextField for stock symbol
   private JLabel stockSymbolJLabel;
   private JTextField stockSymbolJTextField;

   // JLabel and JTextField for number of shares
   private JLabel sharesJLabel; 
   private JTextField sharesJTextField;

   // JLabel and JTextField for price of shares
   private JLabel priceJLabel;
   private JTextField priceJTextField;

   // JLabel and JTextField for total value
   private JLabel totalJLabel;
   private JTextField totalJTextField;

   // instance variables for database processing
   private Connection myConnection;
   private Statement myStatement;
   private ResultSet myResultSet;

   // constructor
   public StockPortfolio( String databaseDriver, String databaseURL )
   {
	   // establish a connection to db
	   try
	   {
		   Class.forName ( databaseDriver );
		   
		   // connect to a database
		   myConnection =
		   	DriverManager.getConnection (databaseURL );
		   	
		   	// create Statement for executing SQL
		   	myStatement = myConnection.createStatement();
	   }
	   catch ( SQLException exception )
	   {
		   exception.printStackTrace();
	   }
	   catch ( ClassNotFoundException exception )
	   {
		   exception.printStackTrace();
	   }
	   
      createUserInterface(); // set up GUI

   } // end constructor

   // create and position GUI components; register event handlers
   private void createUserInterface()
   {
      // get content pane for attaching GUI components
      Container contentPane = getContentPane();
      
      // enable explicit positioning of GUI components
      contentPane.setLayout( null );

      // set up prompt1JLlabel
      prompt1JLabel = new JLabel();
      prompt1JLabel.setBounds( 8, 16, 350, 16 );
      prompt1JLabel.setText( "Select the name of " +
         "the stock for which you want " );
      contentPane.add( prompt1JLabel );

      // set up prompt2JLabel
      prompt2JLabel = new JLabel();
      prompt2JLabel.setBounds( 8, 32, 350, 16 );
      prompt2JLabel.setText( "information, and then " +
         "press the Stock Information button." );
      contentPane.add( prompt2JLabel );
      
      // set up stockNamesJComboBox 
      stockNamesJComboBox = new JComboBox();
      stockNamesJComboBox.setBounds( 76, 65, 200, 26 );
      stockNamesJComboBox.addItem( "" );
      contentPane.add( stockNamesJComboBox );
      
      // load stock names into stockNamesJComboBox
      loadStockNames();

      // set up stockInfoJButton
      stockInfoJButton = new JButton();
      stockInfoJButton.setBounds( 100, 100, 150, 23 );
      stockInfoJButton.setText( "Stock Information" );
      contentPane.add( stockInfoJButton );
      stockInfoJButton.addActionListener(

         new ActionListener()  // anonymous inner class
         {
            // event handler called when stockInfoJButton is clicked
            public void actionPerformed( ActionEvent event )
            {
               stockInfoJButtonActionPerformed( event );
            }

         } // end anonymous inner class

      ); // end addActionLstener

      // set up stockInfoJPanel
      stockInfoJPanel = new JPanel();
      stockInfoJPanel.setBounds( 18, 145, 300, 192 );
      stockInfoJPanel.setLayout( null );
      stockInfoJPanel.setBorder( BorderFactory.createTitledBorder( 
         BorderFactory.createEtchedBorder(), "Stock Info" ) );
      contentPane.add( stockInfoJPanel );

      // set up stockNameJLabel
      stockNameJLabel = new JLabel();
      stockNameJLabel.setBounds( 8, 24, 150, 23 );
      stockNameJLabel.setText( "Stock name:" );
      stockInfoJPanel.add( stockNameJLabel );

      // set up stockNameJTextField
      stockNameJTextField = new JTextField();
      stockNameJTextField.setBounds( 158, 24, 125, 24 );
      stockNameJTextField.setEditable( false );
      stockNameJTextField.setBorder( 
         BorderFactory.createLoweredBevelBorder() );
      stockNameJTextField.setHorizontalAlignment( 
         JTextField.CENTER );
      stockInfoJPanel.add( stockNameJTextField );

      // set up stockSymbolJLabel
      stockSymbolJLabel = new JLabel();
      stockSymbolJLabel.setBounds( 8, 56, 150, 23 );
      stockSymbolJLabel.setText( "Stock symbol:" );
      stockInfoJPanel.add( stockSymbolJLabel );

      // set up stockSymbolJTextField
      stockSymbolJTextField = new JTextField();
      stockSymbolJTextField.setBounds( 158, 56, 125, 24 );
      stockSymbolJTextField.setEditable( false );
      stockSymbolJTextField.setBorder( 
         BorderFactory.createLoweredBevelBorder() );
      stockSymbolJTextField.setHorizontalAlignment( 
         JTextField.CENTER );
      stockInfoJPanel.add( stockSymbolJTextField );

      // set up sharesJLabel
      sharesJLabel = new JLabel();
      sharesJLabel.setBounds( 8, 88, 150, 23 );
      sharesJLabel.setText( "Number of shares:" );
      stockInfoJPanel.add( sharesJLabel );

      // set up sharesJTextField
      sharesJTextField = new JTextField();
      sharesJTextField.setBounds( 158, 88, 125, 24 );
      sharesJTextField.setEditable( false );
      sharesJTextField.setBorder( 
         BorderFactory.createLoweredBevelBorder() );
      sharesJTextField.setHorizontalAlignment( JTextField.CENTER );
      stockInfoJPanel.add( sharesJTextField );

      // set up priceJLabel
      priceJLabel = new JLabel();
      priceJLabel.setBounds( 8, 120, 150, 23 );
      priceJLabel.setText( "Price per share:" );
      stockInfoJPanel.add( priceJLabel );

      // set up priceJTextField
      priceJTextField = new JTextField();
      priceJTextField.setBounds( 158, 120, 125, 24 );
      priceJTextField.setEditable( false );
      priceJTextField.setBorder( 
         BorderFactory.createLoweredBevelBorder() );
      priceJTextField.setHorizontalAlignment( JTextField.CENTER );
      stockInfoJPanel.add( priceJTextField );

      // set up totalJLabel
      totalJLabel = new JLabel();
      totalJLabel.setBounds( 8, 152, 150, 23 );
      totalJLabel.setText( "Total value:" );
      stockInfoJPanel.add( totalJLabel );

      // set up totalJTextField
      totalJTextField = new JTextField();
      totalJTextField.setBounds( 158, 152, 125, 24 );
      totalJTextField.setEditable( false );
      totalJTextField.setBorder( 
         BorderFactory.createLoweredBevelBorder() );
      totalJTextField.setHorizontalAlignment( JTextField.CENTER );
      stockInfoJPanel.add( totalJTextField );

      // ensure database connection is closed 
      // when user quits application
      addWindowListener(

         new WindowAdapter()  // anonymous inner class
         {
            public void windowClosing( WindowEvent event )
            {
               frameWindowClosing( event );
            }

         } // end anonymous inner class

      ); // end addWindowListener

      // set properties of application's window
      setTitle( "Stock Portfolio" ); // set title bar string
      setSize( 350, 380 );           // set window size
      setVisible( true );            // display window

   } // end method createUserInterface

   // load stock names into stockNamesJComboBox
   private void loadStockNames()
   {
      // add stock names in database to stockNamesJComboBox
      try
      {
	      myResultSet = myStatement.executeQuery(
	      	"SELECT stockNames FROM stockInformation" );
	      
	      // add stockNames to stockNamesJComboBox
	      while ( myResultSet.next() )
	      {
		      stockNamesJComboBox.addItem(
		      	myResultSet.getString ( "stockNames" ) );
		  }
		  
		  myResultSet.close(); // close myResultSet
		  
	  }// end try
	  
	  catch ( SQLException exception)
	  {
		  exception.printStackTrace();
	  }
      
   } // end method loadStockNames

   // user clicked stockInfoJButton
   private void stockInfoJButtonActionPerformed( ActionEvent event )
   {
	   // get selected stock
	  String stockName = 
	  	( String ) stockNamesJComboBox.getSelectedItem(); 
	  	
	  	//display stock data
	  	displayStockData ( stockName );
	  	
	} // end method stockInfoJButtonActionPerformed
	
	//display stock information
	private void displayStockData ( String stockName )
	{
		//display stock name, stock symbol, shares and price
		try
		{
			//get stock name, stock symbol and shares
			myResultSet = myStatement.executeQuery( "SELECT stockSymbol,"
				+ " shares, price FROM stockInformation WHERE " +
				"stockName = " + ( stockName ) );
			
			// non empty result
			if (myResultSet.next () )
			{
				stockNameJTextField.setText(
					myResultSet.getString( "stockName" ) );
				stockSymbolJTextField.setText(
					myResultSet.getString( "stockSymbol" ) );
				sharesJTextField.setText(
					myResultSet.getString( "shares" ) );
				priceJTextField.setText(	
					myResultSet.getString( "price" ) );
			}
			
			myResultSet.close(); // close myResultSet
			
			
			
		}
		catch ( SQLException exception )
      	{
         	exception.printStackTrace();
      	}
	}// end method display stock data
	
	// calculate total value
	private String computeTotalValue( int shares, double price )
	{
		try
		{
			
		//get shares and price
		shares = myResultSet.getInt( "shares" );
		price = myResultSet.getDouble( "price" );

		
		// define display format
		DecimalFormat dollars = new DecimalFormat( "$0.00" );

		return dollars.format( shares * price );
		
		}
		catch ( SQLException exception )
      	{
         	exception.printStackTrace();
      	}
		

	} // end method computeTotalValue

   // user close window
   private void frameWindowClosing( WindowEvent event )
   {
      // close myStatement and database connection
      try
      {
         myStatement.close();
         myConnection.close();
      }
      catch ( SQLException sqlException )
      {
         sqlException.printStackTrace();
      }
      finally
      {
         System.exit( 0 );
      }
      
   }  // end method frameWindowClosing
	
   // method main
   public static void main( String[] args )
   {
      // check command-line arguments
      if ( args.length == 2 )
      {
         // get command-line arguments
         String databaseDriver = args[ 0 ];
         String databaseURL = args[ 1 ];

         // create new StockPortfolio
         StockPortfolio application = 
            new StockPortfolio( databaseDriver, databaseURL );
      }
      else
      {
         System.out.println( "Usage: java StockPortfolio " + 
            "databaseDriver databaseURL" );
      }

   } // end method main

} // end class StockPortfolio

im guessing im starting to go wrong around line 310, but this is my first week with DB's so basic explanations are beneficial!

[pbrockway2]

// calculate total value
private String computeTotalValue( int shares, double price )
{
    try
    {
			
        //get shares and price
        shares = myResultSet.getInt( "shares" );
        price = myResultSet.getDouble( "price" );

		
        // define display format
        DecimalFormat dollars = new DecimalFormat( "$0.00" );

        return dollars.format( shares * price );
		
    }
    catch ( SQLException exception )
    {
        exception.printStackTrace();
    }
} // end method computeTotalValue

You get the "missing return statement" because you have said that this method returns a String and the compiler insists that it will return a string under every normal circumstance. So, basically, if there is an sql exception (that's considered normal because you catch it) you print a stack trace but you don't return a string. And that's what the compiler is complaining about.

What do you intend to happen if there is an exception? Probably answering that will tell you what (if any) string should be returned.

--------------------------

And, generally, people find line numbers make code hard to read and impossible to cut-n-paste.

[hayden06f4i]

i tried adding an additional statement like:

totalNameJTextField.setText( myResultSet.getString( "dollars" ) );

but that cause an additional error, and i really think thats not what i need exactly. but somehow i do need to make the product;

 return dollars.format( shares * price );

show up in the JTextBox, right?

[pbrockway2]

The "missing return statement" has nothing to do with what is displayed in the text box. It is entirely about ensuring that the computeTotalValue() returns a string as it is declared to do.

At the moment that method does not return a string if an exception occurs. You will get the "missing return statement" message until you change the code so that the method does return a string.

[hayden06f4i]

ok, bear with me, im not real knowledgeable with the try/catch things. so there is no return statement in the catch. i understand that now. so i now have 3 questions, haha.

1. in this particular situation....do i NEED to use try/catch anyway?

2. should i return the same return string in the catch method that i do in the try method?

3. should i return some sort of error message in the catch block?

[hayden06f4i]

well scratch #1, because i just tried removing the try and catch and got an error about uncaught exceptions, so i obviously need the try/catch....haha.

tried #2 and got an error "cannot find symbol" on the >dollars.format line in the catch method.

tried #3 JOptionPane.showMessageDialog and still said missing return statement.

also tried just "return;" but that obviously did work either.

i have put in the appropriate effort, can someone look at this closely and tell me exactly what im not understanding? i have tried to reference previous projects i have done, but all the methods that i have worked on previously are type "void" so the catch block hasn't had to return anything. i guess im lost on this.

[pbrockway2]

ok, bear with me, im not real knowledgeable with the try/catch things

No problem. Understanding the try/catch is key, take your time. For a general discussion there are pages in the Exceptions section of Oracle's Tutorial that might help.

The bottom line here is that if anything nasty happens in these two lines

shares = myResultSet.getInt( "shares" );
price = myResultSet.getDouble( "price" );

then you will end up in the "catch" part of the code. (And - to belabour the point - the compiler is insisting that, even then, you must return a string.) The API docs for getInt() describe the sort of thing that will lead to an exception: "the columnLabel is not valid; ... a database access error occurs or this method is called on a closed result set". The first and last cause (probably) represent programming errors you make, but the middle one is something not really under your control.

1. in this particular situation....do i NEED to use try/catch anyway?
2. should i return the same return string in the catch method that i do in the try method?
3. should i return some sort of error message in the catch block?

These are good questions. (and the right ones to be asking). I wish there were easy answers! Number 2 *is* easy: you can't return the string representing the product because it is precisely in creating that string that the exception occurs.

Number 3 is almost as easy - you should probably not return an error message because if you do it will end up being displayed in the text field. This is tacky at best (the user won't know what's going on). More likely it will lead to problems later on if your program uses the value in the text field.

But do you need to use try/catch? That's why I asked before "What do you intend to happen if there is an exception?"

As described in the Tutorial I linked to above, there is an option. You can write:

    /**
     * Returns the total value as a formatted string.
     * @throws SQLException if anything goes wrong
     */
private String computeTotalValue( int shares, double price ) throws SQLException
{
    //get shares and price
    shares = myResultSet.getInt( "shares" );
    price = myResultSet.getDouble( "price" );

    // define display format
    DecimalFormat dollars = new DecimalFormat( "$0.00" );

    return dollars.format( shares * price );
} // end method computeTotalValue

In this case an exception can still happen but it will be "thrown" to whoever calls this method. In other words whoever calls this method (it isn't part of the code you've posted - you probably haven't written that bit yet) will have to do so within a try/catch block.

------------------------------

If the focus of the exercise is on getting and displaying information from the database this approach may be acceptable. (As noted above the cause of the exception is most likely a "database error", whatever that means. You may feel your program knows nothing and can do nothing about it.) But you should realise that the error handling is not very robust.

For instance in the stockInfoJButton click handler you already have a catch block that reports the error but does nothing else. Think about what will actually happen in the event of a random database error. The user will click the button, the error happens and a message will be printed to the console (which the user won't see) instead of the GUI being updated. The user will then cry: "I clicked the button but nothing happened!"

I would say this is completely accceptable in a database exercise where the focus is not on error handling. But - to repeat - you should recognise that in a more robust program some error dialog box would appear and the program gracefully close down (or take some remedial action).

------------------------------

So, the bottom line: in a real program where lives (or at least livelihoods) are on the line you would do something about database failure. But in an exercise you may be prepared to let methods "throw" the exceptions to whatever called them, and button handlers report the error message to the console but otherwise do nothing.

[EDIT] corrected critical bit of code

[pbrockway2]

Sorry: took ages to compose my post, so missed the post above it.

[hayden06f4i]

thank you for your detailed post. i have read through it twice now. im glad i at least posed the appropriate questions, so that it appears that im putting in effort here, and not fishing for answers (although ultimately i need to find the answer to my issue).

so i read it as, in the real world i would/will need more robust error handling, however in this exercise, where the focus is on how connecting to databases work, and not about error handling, it is less crucial.

so i have tried to remove the try and the catch block and just leave the method itself, however, i get 2 errors stating "unreported excepton java.sql.SQLException; must be caught or declared to be thrown."

then it points to the two lines we have discussed....

    shares = myResultSet.getInt( "shares" );
    price = myResultSet.getDouble( "price" );

so is a try/catch statement a MUST? how do i get past this?

[pbrockway2]

I corrected my post to add a critical part to the method:

private String computeTotalValue( int shares, double price ) [b]throws SQLException[/b]
{

Try that and see what happens.

[hayden06f4i]

with your modification the code now compiles.

initially i would get an immediate stack trace and runtime error because the "loadstockNames" method had problems (name mistakes) i fixed those, and now the stockNames load into the combobox, but when i click the JButton i get a an error, and nothing happens. here is the latest code, pointers?

// Exercise 26.11: StockPortfolio.java
// Displays a client's stock portfolio.
import java.awt.*;
import java.awt.event.*;
import java.sql.*;
import java.text.*;
import javax.swing.*;

public class StockPortfolio extends JFrame
{
   // JLabels for prompt
   private JLabel prompt1JLabel;
   private JLabel prompt2JLabel; 

   // JComboBox for stock names
   private JComboBox stockNamesJComboBox;

   // JButton for stock information
   private JButton stockInfoJButton;

   // JPanel for displaying stock information
   private JPanel stockInfoJPanel;

   // JLabel and JTextField for stock name
   private JLabel stockNameJLabel; 
   private JTextField stockNameJTextField;

   // JLabel and JTextField for stock symbol
   private JLabel stockSymbolJLabel;
   private JTextField stockSymbolJTextField;

   // JLabel and JTextField for number of shares
   private JLabel sharesJLabel; 
   private JTextField sharesJTextField;

   // JLabel and JTextField for price of shares
   private JLabel priceJLabel;
   private JTextField priceJTextField;

   // JLabel and JTextField for total value
   private JLabel totalJLabel;
   private JTextField totalJTextField;

   // instance variables for database processing
   private Connection myConnection;
   private Statement myStatement;
   private ResultSet myResultSet;

   // constructor
   public StockPortfolio( String databaseDriver, String databaseURL )
   {
	   // establish a connection to db
	   try
	   {
		   Class.forName ( databaseDriver );
		   
		   // connect to a database
		   myConnection =
		   	DriverManager.getConnection (databaseURL );
		   	
		   	// create Statement for executing SQL
		   	myStatement = myConnection.createStatement();
	   }
	   catch ( SQLException exception )
	   {
		   exception.printStackTrace();
	   }
	   catch ( ClassNotFoundException exception )
	   {
		   exception.printStackTrace();
	   }
	   
      createUserInterface(); // set up GUI

   } // end constructor

   // create and position GUI components; register event handlers
   private void createUserInterface()
   {
      // get content pane for attaching GUI components
      Container contentPane = getContentPane();
      
      // enable explicit positioning of GUI components
      contentPane.setLayout( null );

      // set up prompt1JLlabel
      prompt1JLabel = new JLabel();
      prompt1JLabel.setBounds( 8, 16, 350, 16 );
      prompt1JLabel.setText( "Select the name of " +
         "the stock for which you want " );
      contentPane.add( prompt1JLabel );

      // set up prompt2JLabel
      prompt2JLabel = new JLabel();
      prompt2JLabel.setBounds( 8, 32, 350, 16 );
      prompt2JLabel.setText( "information, and then " +
         "press the Stock Information button." );
      contentPane.add( prompt2JLabel );
      
      // set up stockNamesJComboBox 
      stockNamesJComboBox = new JComboBox();
      stockNamesJComboBox.setBounds( 76, 65, 200, 26 );
      stockNamesJComboBox.addItem( "" );
      contentPane.add( stockNamesJComboBox );
      
      // load stock names into stockNamesJComboBox
      loadStockNames();

      // set up stockInfoJButton
      stockInfoJButton = new JButton();
      stockInfoJButton.setBounds( 100, 100, 150, 23 );
      stockInfoJButton.setText( "Stock Information" );
      contentPane.add( stockInfoJButton );
      stockInfoJButton.addActionListener(

         new ActionListener()  // anonymous inner class
         {
            // event handler called when stockInfoJButton is clicked
            public void actionPerformed( ActionEvent event )
            {
               stockInfoJButtonActionPerformed( event );
            }

         } // end anonymous inner class

      ); // end addActionLstener

      // set up stockInfoJPanel
      stockInfoJPanel = new JPanel();
      stockInfoJPanel.setBounds( 18, 145, 300, 192 );
      stockInfoJPanel.setLayout( null );
      stockInfoJPanel.setBorder( BorderFactory.createTitledBorder( 
         BorderFactory.createEtchedBorder(), "Stock Info" ) );
      contentPane.add( stockInfoJPanel );

      // set up stockNameJLabel
      stockNameJLabel = new JLabel();
      stockNameJLabel.setBounds( 8, 24, 150, 23 );
      stockNameJLabel.setText( "Stock name:" );
      stockInfoJPanel.add( stockNameJLabel );

      // set up stockNameJTextField
      stockNameJTextField = new JTextField();
      stockNameJTextField.setBounds( 158, 24, 125, 24 );
      stockNameJTextField.setEditable( false );
      stockNameJTextField.setBorder( 
         BorderFactory.createLoweredBevelBorder() );
      stockNameJTextField.setHorizontalAlignment( 
         JTextField.CENTER );
      stockInfoJPanel.add( stockNameJTextField );

      // set up stockSymbolJLabel
      stockSymbolJLabel = new JLabel();
      stockSymbolJLabel.setBounds( 8, 56, 150, 23 );
      stockSymbolJLabel.setText( "Stock symbol:" );
      stockInfoJPanel.add( stockSymbolJLabel );

      // set up stockSymbolJTextField
      stockSymbolJTextField = new JTextField();
      stockSymbolJTextField.setBounds( 158, 56, 125, 24 );
      stockSymbolJTextField.setEditable( false );
      stockSymbolJTextField.setBorder( 
         BorderFactory.createLoweredBevelBorder() );
      stockSymbolJTextField.setHorizontalAlignment( 
         JTextField.CENTER );
      stockInfoJPanel.add( stockSymbolJTextField );

      // set up sharesJLabel
      sharesJLabel = new JLabel();
      sharesJLabel.setBounds( 8, 88, 150, 23 );
      sharesJLabel.setText( "Number of shares:" );
      stockInfoJPanel.add( sharesJLabel );

      // set up sharesJTextField
      sharesJTextField = new JTextField();
      sharesJTextField.setBounds( 158, 88, 125, 24 );
      sharesJTextField.setEditable( false );
      sharesJTextField.setBorder( 
         BorderFactory.createLoweredBevelBorder() );
      sharesJTextField.setHorizontalAlignment( JTextField.CENTER );
      stockInfoJPanel.add( sharesJTextField );

      // set up priceJLabel
      priceJLabel = new JLabel();
      priceJLabel.setBounds( 8, 120, 150, 23 );
      priceJLabel.setText( "Price per share:" );
      stockInfoJPanel.add( priceJLabel );

      // set up priceJTextField
      priceJTextField = new JTextField();
      priceJTextField.setBounds( 158, 120, 125, 24 );
      priceJTextField.setEditable( false );
      priceJTextField.setBorder( 
         BorderFactory.createLoweredBevelBorder() );
      priceJTextField.setHorizontalAlignment( JTextField.CENTER );
      stockInfoJPanel.add( priceJTextField );

      // set up totalJLabel
      totalJLabel = new JLabel();
      totalJLabel.setBounds( 8, 152, 150, 23 );
      totalJLabel.setText( "Total value:" );
      stockInfoJPanel.add( totalJLabel );

      // set up totalJTextField
      totalJTextField = new JTextField();
      totalJTextField.setBounds( 158, 152, 125, 24 );
      totalJTextField.setEditable( false );
      totalJTextField.setBorder( 
         BorderFactory.createLoweredBevelBorder() );
      totalJTextField.setHorizontalAlignment( JTextField.CENTER );
      stockInfoJPanel.add( totalJTextField );

      // ensure database connection is closed 
      // when user quits application
      addWindowListener(

         new WindowAdapter()  // anonymous inner class
         {
            public void windowClosing( WindowEvent event )
            {
               frameWindowClosing( event );
            }

         } // end anonymous inner class

      ); // end addWindowListener

      // set properties of application's window
      setTitle( "Stock Portfolio" ); // set title bar string
      setSize( 350, 380 );           // set window size
      setVisible( true );            // display window

   } // end method createUserInterface

   // load stock names into stockNamesJComboBox
   private void loadStockNames()
   {
      // add stock names in database to stockNamesJComboBox
      try
      {
	      myResultSet = myStatement.executeQuery(
	      	"SELECT stockName FROM stockInformation" );
	      
	      // add stockNames to stockNamesJComboBox
	      while ( myResultSet.next() )
	      {
		      stockNamesJComboBox.addItem(
		      	myResultSet.getString ( "stockName" ) );
		  }
		  
		  myResultSet.close(); // close myResultSet
		  
	  }// end try
	  
	  catch ( SQLException exception)
	  {
		  exception.printStackTrace();
	  }
      
   } // end method loadStockNames

   // user clicked stockInfoJButton
   private void stockInfoJButtonActionPerformed( ActionEvent event )
   {
	   // get selected stock
	  String stockName = 
	  	( String ) stockNamesJComboBox.getSelectedItem(); 
	  	
	  	//display stock data
	  	displayStockData ( stockName );
	  	
	} // end method stockInfoJButtonActionPerformed
	
	//display stock information
	private void displayStockData ( String stockName )
	{
		//display stock name, stock symbol, shares and price
		try
		{
			//get stock name, stock symbol and shares
			myResultSet = myStatement.executeQuery( "SELECT stockSymbol,"
				+ " shares, price FROM stockInformation WHERE " +
				"stockName = " + ( stockName ) );
			
			// non empty result
			if (myResultSet.next () )
			{
				stockNameJTextField.setText(
					myResultSet.getString( "stockName" ) );
				stockSymbolJTextField.setText(
					myResultSet.getString( "stockSymbol" ) );
				sharesJTextField.setText(
					myResultSet.getString( "shares" ) );
					
				DecimalFormat price = new DecimalFormat( "$0.00" );
				
				priceJTextField.setText(	
					myResultSet.getString( "price" ) );
			}
			
			myResultSet.close(); // close myResultSet
			
			
			
		}
		catch ( SQLException exception )
      	{
         	exception.printStackTrace();
      	}
	}// end method display stock data
	
	// calculate total value
	private String computeTotalValue( int shares, double price )throws SQLException
	{
		
		//get shares and price
		shares = myResultSet.getInt( "shares" );
		price = myResultSet.getDouble( "price" );

		
		// define display format
		DecimalFormat dollars = new DecimalFormat( "$0.00" );

		return dollars.format( shares * price );

	} // end method computeTotalValue

   // user close window
   private void frameWindowClosing( WindowEvent event )
   {
      // close myStatement and database connection
      try
      {
         myStatement.close();
         myConnection.close();
      }
      catch ( SQLException sqlException )
      {
         sqlException.printStackTrace();
      }
      finally
      {
         System.exit( 0 );
      }
      
   }  // end method frameWindowClosing
	
   // method main
   public static void main( String[] args )
   {
      // check command-line arguments
      if ( args.length == 2 )
      {
         // get command-line arguments
         String databaseDriver = args[ 0 ];
         String databaseURL = args[ 1 ];

         // create new StockPortfolio
         StockPortfolio application = 
            new StockPortfolio( databaseDriver, databaseURL );
      }
      else
      {
         System.out.println( "Usage: java StockPortfolio " + 
            "databaseDriver databaseURL" );
      }

   } // end method main

} // end class StockPortfolio

[hayden06f4i]

my mistake, here is the error:

java.sql.SQLException: [Microsoft][ODBC Microsoft Access Driver] Syntax error (m
issing operator) in query expression 'stockName = CVS Corp'.

[pbrockway2]

when i click the JButton i get a an error

Is this error coming from within displayStockData()? (It's a good idea to post the entire printStackTrace() output)

myResultSet = myStatement.executeQuery( "SELECT stockSymbol,"
        + " shares, price FROM stockInformation WHERE " +
        "stockName = " + ( stockName ) );

I'm wondering about this and the fact that if stockName has the value "CVS Corp" then the space may be causing problems. The database may be saying: he wants data where stockName is CSV but wtf is Corp all about - it's missing an operator.

If other selections (without spaces in the name) are OK this would confirm that the space is the problem.

In this case you could try putting some quotes in as part of the sql string. But a much better way is to use a PreparedStatement:

// instance variables for database processing
private Connection myConnection;
private Statement myStatement;
private PreparedStatement stockDataPS;  // <---
private ResultSet myResultSet;

public StockPortfolio( String databaseDriver, String databaseURL )
{
    // ...
    // create Statement for executing SQL
    myStatement = myConnection.createStatement();
    stockDataPS = myConnection.prepareStatement(
            "SELECT stockSymbol, shares, price FROM stockInformation WHERE stockName = ?");
    // ...
}

// user clicked stockInfoJButton
private void stockInfoJButtonActionPerformed( ActionEvent event )
{
    //...
    private void displayStockData ( String stockName )
    {
        //display stock name, stock symbol, shares and price
        try
        {
            //get stock name, stock symbol and shares
            stockDataPS.setString(1, stockName); // <-- sets the ?
            myResultSet = stockDataPS.executeQuery();
            //...

Prepared statements are designed for reuse, dealing with quoting and other formatting problems in a database independent way, and dealing with "malicious" values being inserted into the sql string. (It is possible to give stockName a value so that the resulting sql query did nasty things to your database.)

---------------------------

I don't know an awful lot about databases - but I'm sure if I'm putting you wrong here someone will jump in and say so!

[Edit] Again forgot a critical bit of code... ;(

[hayden06f4i]

all of the "stockNames" have spaces in them, not that im looking at them, so obviously an error occurs with all of them. here is the entire stack trace error.

c:\SimplyJava\StockPortfolio>java StockPortfolio sun.jdbc.odbc.JdbcOdbcDriver jd
bc:odbc:stocks
java.sql.SQLException: [Microsoft][ODBC Microsoft Access Driver] Syntax error (m
issing operator) in query expression 'stockName = Yahoo INC'.
        at sun.jdbc.odbc.JdbcOdbc.createSQLException(JdbcOdbc.java:6957)
        at sun.jdbc.odbc.JdbcOdbc.standardError(JdbcOdbc.java:7114)
        at sun.jdbc.odbc.JdbcOdbc.SQLExecDirect(JdbcOdbc.java:3110)
        at sun.jdbc.odbc.JdbcOdbcStatement.execute(JdbcOdbcStatement.java:338)
        at sun.jdbc.odbc.JdbcOdbcStatement.executeQuery(JdbcOdbcStatement.java:2
53)
        at StockPortfolio.displayStockData(StockPortfolio.java:281)
        at StockPortfolio.stockInfoJButtonActionPerformed(StockPortfolio.java:27
0)
        at StockPortfolio.access$000(StockPortfolio.java:9)
        at StockPortfolio$1.actionPerformed(StockPortfolio.java:121)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:19
95)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.jav
a:2318)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel
.java:387)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242
)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonL
istener.java:236)
        at java.awt.Component.processMouseEvent(Component.java:6267)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
        at java.awt.Component.processEvent(Component.java:6032)
        at java.awt.Container.processEvent(Container.java:2041)
        at java.awt.Component.dispatchEventImpl(Component.java:4630)
        at java.awt.Container.dispatchEventImpl(Container.java:2099)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577
)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)

        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
        at java.awt.Container.dispatchEventImpl(Container.java:2085)
        at java.awt.Window.dispatchEventImpl(Window.java:2478)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThre
ad.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.
java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThre
ad.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)

        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)

        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

[pbrockway2]

at StockPortfolio.displayStockData(StockPortfolio.jav a:281)

Thanks. That confirms where the exception is happening.

Did you try using a prepared statement?

[hayden06f4i]

I have not tried using a prepared statement yet. I have never used one before, so im trying to understand exactly how it works.

you mentioned trying a simply way with quotes, what would i need to do with that first, to try that out, so im sure that in the final issue?

[pbrockway2]

myResultSet = myStatement.executeQuery( "SELECT stockSymbol,"
        + " shares, price FROM stockInformation WHERE " +  
        "stockName = \'" + ( stockName )  + "\'");

I'm not sure whether single or double quotes are needed. But I am quite sure that prepared statements are better.

[hayden06f4i]

i used your code adjustment, and got this:

c:\SimplyJava\StockPortfolio>javac StockPortfolio.java
StockPortfolio.java:283: cannot find symbol
symbol  : class stockName
location: class StockPortfolio
                                "stockName = '" + ( stockName )"'" );
                                                    ^
1 error

i also found a similar example in this chapters book, identical to yours, but without the backslashes.

i tried both ways, with and without the backslash and got the same compile error.

[pbrockway2]

You've left a + sign out. (Another cost of rolling your own sql expression ;)

"stockName = '" + ( stockName ) [b]+[/b] "'" );

[hayden06f4i]

ahhhhh......man im a rookie!

ok, so it compiles, not at runtime, another error, this time "Column not Found"

wow, im terrible at this!

entire stacktrace:

c:\SimplyJava\StockPortfolio>java StockPortfolio sun.jdbc.odbc.JdbcOdbcDriver jd
bc:odbc:stocks
java.sql.SQLException: Column not found
        at sun.jdbc.odbc.JdbcOdbcResultSet.findColumn(JdbcOdbcResultSet.java:185
0)
        at sun.jdbc.odbc.JdbcOdbcResultSet.getString(JdbcOdbcResultSet.java:411)

        at StockPortfolio.displayStockData(StockPortfolio.java:288)
        at StockPortfolio.stockInfoJButtonActionPerformed(StockPortfolio.java:27
0)
        at StockPortfolio.access$000(StockPortfolio.java:9)
        at StockPortfolio$1.actionPerformed(StockPortfolio.java:121)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:19
95)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.jav
a:2318)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel
.java:387)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242
)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonL
istener.java:236)
        at java.awt.Component.processMouseEvent(Component.java:6267)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
        at java.awt.Component.processEvent(Component.java:6032)
        at java.awt.Container.processEvent(Container.java:2041)
        at java.awt.Component.dispatchEventImpl(Component.java:4630)
        at java.awt.Container.dispatchEventImpl(Container.java:2099)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577
)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)

        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
        at java.awt.Container.dispatchEventImpl(Container.java:2085)
        at java.awt.Window.dispatchEventImpl(Window.java:2478)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThre
ad.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.
java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThre
ad.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)

        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)

        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

if i better understood reading the stack trace i could try some things, but im not really sure what im reading....