Mac and Java 1.6 (or the lack thereof)
Java SE provides a great opportunity to create applications that will run on Windows, Linux and Mac from the same single .jar executable file. All the end user needs is Java installed, and this is installed as standard for many OSes.
Unfortunately at the time of writing, Jan 2008, there is a problem with targeting Macs. Even the latest version of the Mac operating system OSX 10.5 (Leapard) does not include the latest version of Java, 1.6, that has been the default in Windows-based Java IDEs for a year at least.
A beta can be downloaded but this requires registration on the developer sites, cannot run on OSX 1.4 (Tiger), requires an Intel 64 bit processor, and has other restrictions. Right now it’s far from ideal for a mainstream application, and it’s hard to imagine that even when released officially 1.6 will reach a critical mass of deployment until 2009 at least.
The Windows NetBeans to Mac problem
Unfortunately GUI applications developed with the latest Windows NetBeans 5.5 (the free Java API from Sun) require some configuration to allow applications to be developed that run on out-of-the-box Macs. This is not just because of the OSX Java 1.6 problem, but also some glitches with the “backport” targeting in NetBeans. This affects GUI applications developed with NetBeans GUI editor which uses Swing, a cross-platform GUI layer for Java.
It is not enough to set the source level to 1.5 in the project properties, but to continue to use the 1.6 JDK. This will not run on OSX with 1.5 JRE. The error in the Console will be:
The problem is that when using NetBeans’ Swing editor with the 1.6 JDK will create code that won’t run on machines that have Java 1.5. This is because it inserts references to javax.swing.GroupLayout, which only exists in 1.6 onwards. Misleadingly, it does this even if ‘source level’ is set to 1.5.
This can be fixed by downloading the 1.5 JDK (aka the Java Development Kit 5.0 Update 14) and set your NetBeans project to use it. When new Swing GUI elements are created with this JDK set, the IDE uses the org.jdesktop.layout.GroupLayout class instead. This is not built into the JRE but the additional files can be bundled in your .jar. More about this in a second.
The file you require is jdk-1_5_0_14-windows-i586-p.exe and can be downloaded from Sun. Once installed, in NetBeans select Tools->Java Platform Manager. Click Add Platform and choose C:\Program Files\Java\jdk1.5.0_14.
In your applications, in the properties panel, select Libraries, then set the Java Platform to Java Hotspot(TM) Client VM 1.5.0 14-b03 which should now be available. It is important that you do this before you add any Frames as the act of doing this generates the code that must use the correct version of GroupLayout.
The last step is to ensure that the files that 1.5 users (i.e. Mac users) will require are bundled into your .jar, follow the instructions here.
Following these instructions will results in a .jar file that can run on any out-of-the-box installation of OSX, Windows (with latest Java), or Linux.
A great benefit of cross-platform Java SE with Swing is that you can create applications that use all the standard “native” GUI controls for the platforms on which they run. The end-user will have little idea that Java was used, they’ll just see it as an application that looks like it was developed for their choice of OS. To make your Swing applications use native look and feel, follow the instructions under “Programatically Setting the Look and Feel” here