[newbie] Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException:

[jon80]

Any ideas?

1. What is the location of the file?
2. Why include "" next to the properties (see code)?

NOTE: I copied this code from a bowk..

:confused:

[B]PropertiesTest.java[/B]
package homenetwork.bkr.training;

import java.awt.EventQueue;
import java.awt.event.*;
import java.io.*;
import java.util.Properties;
import javax.swing.*;

/** A program to test properties.  The program remembers the 
 * frame position, size, and title.
 */
public class PropertiesTest {
	
	public static void main (String[] args)
	{
		EventQueue.invokeLater(new Runnable()
		{
			public void run()
			{
				PropertiesFrame frame = new PropertiesFrame();
				frame.setVisible(true);
			}
		});
	}

}


[B]PropertiesFrame.java[/B]
package homenetwork.bkr.training;

import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.*;
import java.util.Properties;
import javax.swing.*;


/**
 * A frame that restores position and size from a properties file and updates
 * the properties upon exit.
 */
@SuppressWarnings("serial")
public class PropertiesFrame extends JFrame {
	
	public PropertiesFrame()
	{
		//get position, size and title from properties
		String userDir = System.getProperty("user.home");
		File propertiesDir = new File(userDir, ".corejava");
		if (!propertiesDir.exists()) propertiesDir.mkdir();
		propertiesFile = new File(propertiesDir, "program.properties");
		
		Properties defaultSettings = new Properties();
		defaultSettings.put("left", 0);
		defaultSettings.put("top", 0);
		[B]defaultSettings.put("width", "" + DEFAULT_WIDTH);[/B]
		[B]defaultSettings.put("height", "" + DEFAULT_HEIGHT); //why include a blank string ""?[/B]
		defaultSettings.put("title", "");
		settings = new Properties(defaultSettings);
		
		if (propertiesFile.exists())
			try
				{
					FileInputStream in = new FileInputStream(propertiesFile);
					settings.load(in);
				}
			catch (IOException ex)
				{
					ex.printStackTrace();
				}
			
		[B]int left = Integer.parseInt(settings.getProperty("left")); //code breaks here[/B]
		int top = Integer.parseInt(settings.getProperty("top"));
		int width = Integer.parseInt(settings.getProperty("width"));
		int height = Integer.parseInt(settings.getProperty("height"));
		setBounds(left, top, width, height);
		
		//if no title given, ask user
		String title = settings.getProperty("title");
		if (title.equals("")) title = JOptionPane.showInputDialog("Please supply a frame title:");
		if (title == null) title = "";
		setTitle(title);
		
		addWindowListener(new WindowAdapter()
		{
			public void windowClosing(WindowEvent event)
			{
				settings.put("left", "" + getX());
				settings.put("top", "" + getY());
				settings.put("width", "" + getWidth());
				settings.put("height", "" + getHeight());
				settings.put("title", getTitle());
				
				try 
				{
					FileOutputStream out = new FileOutputStream(propertiesFile);
					settings.store(out, "Program Properties");
				}
				catch (IOException ex)
				{
					ex.printStackTrace();
				}
				System.exit(0);
			}
		});
	}

	private File propertiesFile;
	private Properties settings;
	
	public static final int DEFAULT_WIDTH = 300;
	public static final int DEFAULT_HEIGHT = 200;
}

Error:
Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: null
at java.lang.Integer.parseInt(Unknown Source)
at java.lang.Integer.parseInt(Unknown Source)
at homenetwork.bkr.training.PropertiesFrame.<init>(Pr opertiesFrame.java:44)
at homenetwork.bkr.training.PropertiesTest$1.run(Prop ertiesTest.java:20)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilter s(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(U nknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

[hardwired]

What is the location of the file?
Have a look:

import java.io.*;

public class Test {
    public static void main(String[] args) {
        String userDir = System.getProperty("user.home");
        System.out.println("userDir = " + userDir);
        File propertiesDir = new File(userDir, ".corejava");
        System.out.println("propertiesDir = " + propertiesDir.getPath());
        if (!propertiesDir.exists()) propertiesDir.mkdir();
        File propertiesFile = new File(propertiesDir, "program.properties");
        System.out.println("propertiesFile = " + propertiesFile.getPath());
    }
}

Why include "" next to the properties
Do you mean in the put method statements, like this?

defaultSettings.put("width", "" + DEFAULT_WIDTH);

It's a trick way to make a String.

[jon80]

The only problem is that I could not find say "user.home" anywhere on my hdd.

Can you expand on why this trick is needed?

[hardwired]

The only problem is that I could not find say "user.home" anywhere on my hdd.
That's because it is a java property key. Run the Test app and see what the output is — it will show you the address of your home folder.

Can you expand on why this trick is needed?
Look up the put method in the Properties class api:
You find it down in the section Methods inherited from class java.util.Hashtable. Follow the put link:
The Hashtable put method takes an Object; in this app a String.
DEFAULT_WIDTH is a primitive data type int.
If you didn't use the trick to make a String you would do

defaultSettings.put("width", String.valueOf(DEFAULT_WIDTH));