Question: How many lines of code does it take to display a window?
Answer: One, but you'll spend the rest of your life rewriting it.
OK, so it's not a particularly funny joke, but it does get to the heart of why so many people originally embraced the Java platform's promise of "write once, run anywhere." Here's a graphical user interface (GUI) development conundrum: each platform has a set of specific guidelines for what is considered the proper look and feel, yet users often want to access an application across multiple platforms. Just look at the variety of development tools described earlier; the installation for many IDEs, such as NetBeans, involves selecting which user interface you'd like to work with.
The long and the short of it is that there is no one right answer for GUI construction. From overt issues, such as the menu structure defaults (where is the placement of the Preferences menu item: the File, Edit, or Application menu?), to subtle ones, such as the default layout for dialog buttons, to paradigm decisions, such as requiring the use of the second mouse button?it's hard to imagine a single approach to GUI application programming that would satisfy all application development needs.
Instead of focusing on the theoretical debate, it is often more useful to consider two key factors: the intended audience and the available resources. If you know that you will develop a consumer application on a large budget, you may wish to build a multimedia-style interface, with an emphasis on graphics, single-click actions, and lots of mouse-rollover responses. If you're building a developer tool in your spare time, you'll probably want to rely on standard Java Metal user interface objects. If you're developing a general productivity application or an in-house application for a corporate environment, you may want to build and test for both Metal on Windows and Unix and Aqua on Mac OS X.
That said, it's often easiest for GUI programmers to begin with the Mac OS X Aqua interface rather than the standard Metal look and feel. Perhaps the best reason to start with Aqua is its sheer number of default components. Aqua has one of the largest sets of defaults for spacing and fonts of any platform. If you start with Aqua, you're less likely to have problems with other platforms (including both Motif and Windows) when you switch to Metal, because your defaults will all be set correctly. In addition, the graphics-intensive nature of the Aqua platform tends to push the limits of a graphics card; if your application responds well under Aqua, less sophisticated user interfaces should be at least as responsive, if not more so.