Software Salariman

Finished a longish article, with sample source code, about writing a simple desktop application in Java and Swing. It discusses model-view-controller, Java resource bundles and Swing AbstractAction.

This blog entry is used for discussion, if any.

Labels: Java, Programming

Groovy is scripting language on the Java platform. Groovy is interesting because it can be compiled into Java byte-code and makes heavy use of closures.

Groovy Hello World

In the beginning, I ported my Jython version into Groovy. It looks pretty much the same as the Jython version:

// Hello World in Groovy
f = new javax.swing.JFrame("Hello World")
f.setSize(170,70)
f.contentPane.layout = new java.awt.FlowLayout()
f.defaultCloseOperation = javax.swing.JFrame.EXIT_ON_CLOSE
f.add(new javax.swing.JLabel("Label me:"))
f.add(new javax.swing.JButton("Press me"))
f.show()

Groovy + SwingBuilder Hello World

Groovy has a helper class called SwingBuilder to make it much easier to write Swing applications. Here's one way to re-write the program:

// Hello World Window in Groovy + SwingBuilder
sb = new groovy.swing.SwingBuilder()
f = sb.frame(
  title:"Hello World"
  ,size:[170,70]
  ,defaultCloseOperation: javax.swing.JFrame.EXIT_ON_CLOSE) {
  flowLayout()
  label(text:"Label me:")
  button(text:"Press me")
}
f.show()

SwingBuilder is quite wonderful because it allows you to define a GUI with a minimum of code noise. The definition of a JFrame probably maps a keyword X to a setX() function but I haven't worked out how SwingBuilder converts words such as flowLayout(), label and button to Swing objects and functions.

Labels: Groovy, Java

The Python language has been ported to two major virtual machine platforms: IronPython for Microsoft .Net and Jython for Java. To get a flavour of these implementations, here are two Hello World scripts that open a window containing a label and a button.

IronPython Hello World Window

import clr
clr.AddReference("System.Drawing")
from System.Drawing import ContentAlignment, Size
clr.AddReference("System.Windows.Forms")
from System.Windows.Forms import Button, FlowLayoutPanel, Form, Label

p = FlowLayoutPanel()
p.Controls.Add(Label(Text="A label:", Size=Size(50,20), TextAlign=ContentAlignment.BottomLeft))
p.Controls.Add(Button(Text="Press Me"))
f = Form(Text="Hello World", Size=Size(160,70))
f.Controls.Add(p)
f.ShowDialog()

Jython Hello World Window

# Jython Hello Window
from java.awt import FlowLayout
from javax.swing import JButton, JFrame, JLabel

f = JFrame("Hello", defaultCloseOperation=JFrame.DISPOSE_ON_CLOSE, size=(170,70), layout=FlowLayout())
f.add(JLabel("A label:"))
f.add(JButton("Press Me"))
f.show()

Mini Observations

• IronPython makes loading the .Net libraries explicit by using the clr module.
• Both implementations allow setX functions in object constructor's argument list.

Labels: DotNet, Java, Python

A colleague got a new computer and when he tried to connect to an Oracle server with a JDBC client, he got this error:

ORA-12705: Cannot access NLS data files or invalid environment specified

After comparing our Java environments, he found that he had user.country = BZ (BZ is the top level domain for Belize). He changed his Regional and Language Options to English (Australia) and then he had no problems connecting to the Oracle server.

I think when JDBC client tries to connect to the Oracle server, the client specifies its locale and when the Oracle server fails to find the required locale files, the server throws the ORA-12705 error message.

Labels: Java, Oracle

Connecting JDBC-based tools such as SQL Developer or DbVisualizer to SQL Server Express required the following steps:

• Obtain JDBC Driver
• TCP/IP for SQL Server Express
• Authentication Method

Obtain JDBC Driver

Using SQL Developer, when you get the following exception …

Unable to find driver: net.sourceforge.jtds.jdbc.Driver

… download the jTDS JDBC driver and install it in your JRE's ext folder. The latest version of the driver is 1.2. Of course, there are other JDBC drivers for SQL Server you can use.

TCP/IP for SQL Server Express

By default, TCP/IP for SQL Server Express is disabled, so JDBC cannot connect to it and you may get the following exception …

Network error IOException: Connection refused: connect

Enable TCP/IP

To enable TCP/IP, start SQL Server Configuration Manager.

1. Expand SQL Server 2005 Network Configuration node.
2. In the right pane, select Protocols for SQLEXPRESS. The right pane should now show Protocols and Status columns.
3. Select Enable from the TCP/IP context menu.

Find or Configure TCP/IP Port

After enabling TCP/IP, you have to find out which port number to use. SQL Server Express allocates a port dynamically each time it is started, so to find or configure the port number, continue using SQL Server Configuration Manager …

1. Select Properties from the TCP/IP context menu. The TCP/IP Properties dialog should open.
2. Select the IP Addresses tab.
3. In the IPAll node …
   1. The TCP Dynamic Ports field shows the currently used port number. If you set that field to blank, then SQL Server Express should not automatically choose another port when it restarts.
   2. Set the desired port number in the TCP Port field.
   3. Press OK to apply your settings and close the dialog.

Test TCP/IP

If you change the TCP/IP port, you have to restart SQL Server Express before it can use the new port number. To test that your port number is used, start a cmd window and type: netstat -an. For instance, if you used port 1433, you should see this line in the list of ports used:

TCP    0.0.0.0:1433           0.0.0.0:0              LISTENING

Authentication Method

By default, SQL Server Express uses Windows Authentication Mode to authenticate connections. If you get this exception …

Login failed for user '<User name>'. The user is not associated with a trusted SQL Server connection.

… then you may have to enable SQL Server Authentication Mode and create or enable a user.

1. Start Microsoft SQL Server Management Studio Express (SSMSE) and connect to your database server.
2. In Object Explorer pane, select Properties from your database's context menu. The Server Properties dialog should open.
3. Select Security page.
4. Select SQL Server and Windows Authentication Mode check box.
5. Press OK button to close the dialog.
6. In Object Explorer pane, expand Security / Logins node.
7. Select existing user sa. Note that there is a red downward arrow next to that user's image.
8. View sa's properties. The Login Properties dialog should open.
9. Select Status page.
10. Ensure that the Login: Enabled radio button is selected.
11. Select General page.
12. Enter a password for this user.
13. Press OK button to close the dialog.
14. If you refresh the Object Explorer pane, note that user sa no longer has a red downward arrow.

Finally …

After all these steps, you should be able to connect to your SQL Server Express database using JDBC.

Labels: Database, Java

I had a play with two Java IDEs recently: Jgrasp and Eclipse. For a developer, Jgrasp was small and worked reasonably well. Since I was trying to fix someone else's code, I wished Jgrasp had more features and shortcut keys for debugging. Eclipse is huge but I like the way it automatically parsed my source code to find errors and warnings.

Labels: Java

The easiest way to display a double in the local currency is to get an instance of NumberFormat currency formatter and use its format() method. The following example ...

import java.text.NumberFormat;

public class CurrencyFormatExample {
  public static void main(String[] argv) {
    NumberFormat cf = NumberFormat.getCurrencyInstance();
    double cost = 19.51;
    System.out.println("Cost = " + cf.format(cost));
  }
}

... produces ...

Cost = $19.51

Similarly, the easiest way to display a date is to get an instance of a DateFormat date formatter and use its format() method. Choose different types of date formatters to produce shorter or longer output. The following example creates four different data formatters ...

import java.text.DateFormat;
import java.util.Date;

public class DateFormatExample {
  public static void main(String[] argv) {
    DateFormat dfShort = DateFormat.getDateInstance(DateFormat.SHORT);
    DateFormat dfMedium = DateFormat.getDateInstance(DateFormat.MEDIUM);
    DateFormat dfLong = DateFormat.getDateInstance(DateFormat.LONG);
    DateFormat dfFull = DateFormat.getDateInstance(DateFormat.FULL);
    Date today = new Date();
    System.out.println("Today is ...");
    System.out.println(dfShort.format(today));
    System.out.println(dfMedium.format(today));
    System.out.println(dfLong.format(today));
    System.out.println(dfFull.format(today));
  }
}

... and produces ...

Today is ...
26/04/05
26/04/2005
26 April 2005
Tuesday, 26 April 2005

Labels: Java, Programming