We Keep Coding

Changing LaF based on OS

Im building a GUI in Netbeans, it looks good in the designer but when I run the program it looks pretty rubbish. Im using a Mac and so I feel that it would look better using the Mac OS LAF but then when I run it on Windows, what will happen? Is a Windows system able to use the Mac LAF and vice-versa?
I dont usually mind the Ocean/Metal LAF but it looks better on Windows than it does on Mac, is there a way to set a theme as a fallback? Or to change depending on the system its running on?

The UIManager.setLookAndFeel(String className) Loads the LookAndFeel specified by the given class name:className, using the current thread's context class loader.
To set look and feel of your current system, make use of UIManager.getSystemLookAndFeelClassName(): Returns the name of the LookAndFeel class that implements the native system look and feel if there is one, otherwise the name of the default cross platform LookAndFeel class.
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
put this code before you create instance of your application window: JFrame or any such Top-level Container.

Look and feel setup for different OS

I want to run my application in different platform and i want to use different look and feel for each platform. could you please guide how can approach this?
This is what i did.
in main java class i added static block and by adding below condition.
if(System.getProperty("os.name").startsWith("Windows")) //Added for linux
{
UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
}
else
{
UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");
}
When I run my application in linux platform, it is not showing metal look and feel rather it's showing java default look and feel mainly in JOptionPane.

Perhaps your answer is available here: http://docs.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
Or read into this SO question:
How to set jframe look and feel

Use the System Look And Feel.
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

Why in my Java application am I seeing "strange" scrollbars?

In my Java application I have a window which holds a JTextArea within a JScrollPane with scrollbars policies set to AS_NEEDED.
As I run my application I see that JTextArea this way:
Why am I seeing the scrollbars with that cutaway knob (which doesn't reflect a "standard" representation like this)?
The Layout for the frame is GridBagLayout, and I'm on Mac OS X 10.8.2, should that matter.

This is based on the Look and Feel your app is using, and the limitations of Java's integration with the native OS layout components. The one in your screenshot looks like Nimbus.
Swing applications always custom-render the look and feel, and don't do a very good job of using the native OS widgets everywhere. The result is that you get weird looks that might be consistent the OS only some of the time, or only with certain layout components.
Welcome to developing cross-platform desktop apps in Java. :(

To attempt to get the system look and feel when your application starts you can do this:
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassname());
} catch (Exception e) {
// Handle exception
}
This will set the look and feel to that of the system regardless of what you run it on.
And as mentioned, the default look and feel for your application appears to be Nimbus and not OSX's Aqua, which again can be fixed with he above snippet and you could (should you care to) offer a UI option to the user to change the look and feel of the application to whatever they chose.

You are with Nimbus LookAndFeel
http://docs.oracle.com/javase/tutorial/uiswing/lookandfeel/nimbus.html

Look and Feel in Swing

The default Look & Feel of Swing is not good looking for Linux platforms, The target Platforms are Windows and Linux, Can someone suggest are there any library which gives better look and feel similar to components appearing on windows platforms for Linux systems?
For windows, I am using system look and feel, this looks much better than in Linux. Also like to know how to load different look and feel depending on the platform.

You'll need to read the 'howto' for setting the look and feel. Oracle has one here: http://docs.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
To use GTK, you would use:
try
{
UIManager.setLookAndFeel("com.sun.java.swing.plaf.gtk.GTKLookAndFeel");
}
catch (ClassNotFoundException e)
{
}
catch (UnsupportedLookAndFeelException e)
{
}

Swing UI does not have native OS look

I am building an application in java swing and I am using the following code to give the UI a native OS look
try {
UIManager.setLookAndFeel(
UIManager.getSystemLookAndFeelClassName());
} catch (Exception e) {
e.printStackTrace();
}
On a OS X, the look is fine, but on windows (XP and 7) the buttons look like this.
alt text http://img710.imageshack.us/img710/8735/buttonsoc.png
I have used this exact same code on other projects and it works fine. But in this particular project I get a completely different look.
I am using Java 1.6
Thanks in advance!

Are you possibly creating your GUI elements before actually setting the L&F? If you already created (e.g.) JButton instances and called methods on them, they allocate their UI peer - changes to the L&F after that won't affect the already created instances.
This would explain why it works on Mac (the L&F defaults to Mac on Apple's JVM IIRC), but not on Windows. You can test this quickly if you move setting the L&F directly into your main method as the very first call (this assuming your main class does NOT contain any statically initialized GUI instances of course).