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ExchangeRateCalculator.java
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/*
* Author: Havard Rast Blok
* E-mail: 
* Web : www.rememberjava.com
*/
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
import javax.swing.*;
/**
* Reads a web page and extracts exchange rate information.
* This information is used in a simple calculator.
*
* It is designed for the "Aftenposten valutakurser" web page:
* http://www.aftenposten.no/nyheter/okonomi/
* However, it should be fairly easy to adjust to other's.
*
* IMPORTANT!
* Aftenposten is a registered tradmark, and this program
* is for educational purposes only.
*/
public class ExchangeRateCalculator extends JFrame implements ItemListener, KeyListener
{
//parsing information (from the week 48-2001 program)
private final String startRates = "<table width=100%>";
private final String startInfo = "sans-serif\">";
private final String endInfo ="</font";
private final String endRates = "</TABLE>";
private final int currencies = 20;
//GUI
private Container c;
private JLabel localLabel;
private JTextField localText, foreignText;
private JComboBox currency;
private float rate;
private String currencyNames[];
private float rates[];
public ExchangeRateCalculator( URL theURL )
{
super( "Exchange Rate Calculator" );
//load exchange rates
loadRates( theURL );
//set up GUI
setSize(250, 150);
c = getContentPane();
c.setLayout( new GridLayout( 2, 2 ) );
localLabel = new JLabel( "Local currency" );
localText = new JTextField();
localText.addKeyListener( this );
foreignText = new JTextField();
foreignText.addKeyListener( this );
currency = new JComboBox( currencyNames );
currency.addItemListener( this );
c.add( localLabel );
c.add( localText );
c.add( currency );
c.add( foreignText );
//update current rate by faking selection
itemStateChanged(null);
pack();
show();
}
/**
* Update the local currency text field based upon the value
* in the foreign text field.
*/
private void updateLocal()
{
float value;
try
{
value = Float.parseFloat( foreignText.getText() );
localText.setText( "" + (value*rate) );
}
catch(NumberFormatException e)
{
System.out.println("ExchangeRateCalculator.updateLocal - error parsing: "+e);
}
}
/**
* Update the foreign currency text field based upon the value
* in the local text field.
*/
private void updateForegin()
{
float value;
try
{
value = Float.parseFloat( localText.getText() );
foreignText.setText( "" + (value*rate) );
}
catch(NumberFormatException e)
{
System.out.println("ExchangeRateCalculator.updateForegin - error parsing: "+e);
}
}
public void keyTyped( KeyEvent e )
{
//System.out.println("keyTyped");
}
public void keyPressed(KeyEvent e)
{
//System.out.println("keyPressed");
}
/**
* Detect a change in the text field and
* change the calulated value.
*/
public void keyReleased(KeyEvent e)
{
//System.out.println("keyReleased");
Object source = e.getSource();
if( source == localText )
{
updateForegin();
}
else if( source == foreignText )
{
updateLocal();
}
}
/**
* Sets the current rate based upon the selected
* country from the list.
*/
public void itemStateChanged(ItemEvent e)
{
int index = currency.getSelectedIndex();
rate = rates[index];
localText.setText("0.0");
foreignText.setText("0.0");
}
/**
* Load the exchange rates from web (or a local file)
* (from the week 48-2001 program)
* @param theURL web or local URL for the file
*/
public void loadRates( URL theURL )
{
BufferedReader bufReader;
String line;
boolean foundRates;
int startInfoLength;
int infoIndex;
int endIndex;
String infoString;
boolean done;
int colCounter;
int rowCounter;
String info[][];
//init variables
foundRates = false;
done = false;
startInfoLength = startInfo.length();
colCounter = 0;
rowCounter = 0;
info = new String[currencies][4];
currencyNames = new String[currencies];
rates = new float[currencies];
try
{
//open web page
bufReader = new BufferedReader( new InputStreamReader(theURL.openStream()) );
//read line by line
while( (line = bufReader.readLine()) != null && !done )
{
//System.out.println(line);
//check if the exchange rate table is found
if( !foundRates )
{
//if not, check if it starts in this line
foundRates = (line.indexOf(startRates) != -1);
}
//check if this line contains interesing information
else if( ( infoIndex = line.indexOf(startInfo)) != -1 )
{
//if it does, check if it is of the first four coloumns
//(The 5th is yesterday's news...)
if( colCounter < 4 )
{
//extract the information
//(no number conversion is done here)
endIndex = line.indexOf(endInfo);
infoString = line.substring( infoIndex + startInfoLength, endIndex );
//put it in a 2d array
info[rowCounter][colCounter] = infoString;
colCounter++;
}
else
{
//end of row (both on web page and in array)
rowCounter++;
colCounter = 0;
}
}
//check if exchange rate table is finished
else if( line.indexOf( endRates ) != -1 )
{
done = true;
}
}
//close the file when finished
bufReader.close();
}
catch( IOException e )
{
System.out.println( "ShowRate.ShowRate - error opening or reading URL: " + e );
}
//Extract names and calclate real rate (by 1 unit, not 100 or 1000)
for(int i = 0; i < currencies; i++)
{
currencyNames[i] = info[i][1] + " - " + info[i][2];
rates[i] = Float.parseFloat( info[i][0] ) * Float.parseFloat( info[i][3] );
}
}
public static void main( String args[] )
{
try
{
new ExchangeRateCalculator( new URL( "http://www.aftenposten.no/nyheter/okonomi/article.jhtml?articleID=34015&vistype=valutakurser" ) );
//Open web page
//new ExchangeRateCalculator(new URL(args[0]));
//Open from local file
//File f = new File( args[0] );
//new ExchangeRateCalculator( f.toURL() );
}
catch (MalformedURLException e)
{
System.out.println("ExchangeRateCalculator.main - wrong url: " +e );
}
}
}
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