The Win32-Java hybrid

Worried that your Java apps won't run on Windows? Here's a strategy that blends the best of Java with Win32 to create applications that run on Microsoft OSs

By Jeff Friesen, JavaWorld.com, 07/01/99

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The text editor application is called te. The Java section of the program was built using JDK 1.2. The C portion was built using Borland C++ 4.52. (Yes, you can write meaningful WJH applications using a non-Visual C++ development tool.)

Table 2 identifies the source and executable files that constitute the Java section of the program. These files are distributed in an archive called te-java.zip. To download these sample code files, click here.

Table 3 identifies the source and executable files that constitute the C portion of the WJH. These files are distributed in an archive called te-c.zip. To download these sample code files, click here.

If you want to learn how te works, first study te.c (the source for te.exe) and then te.java (the source for te.class).

For the purposes of this article, it isn't necessary to go through all of te.c, since it contains a generous helping of comments. However, there are a few observations worth noting.

As you probably know, there are two kinds of Windows applications: console-based and GUI (graphical user interface)-based. This example utilizes a console-based format for te.exe; however, it doesn't matter whether or not you choose console or GUI as your compiler option when creating WJH applications, because the Win32 part of the app wouldn't normally register window classes, create windows, or contain messaging loops.

In the example, we disabled Ctrl-Break key presses so that they won't disrupt te. You can do this by calling the Win32 SetConsoleCtrlHandler API. Without this call, the JVM could abort while executing Java instructions and remaining code in the Win32 executable wouldn't be reached. Do you have to disable Ctrl-Breaks? That depends upon your application, but it's always better to play it safe.

The LoadJVM function (in te.c) queries the Windows registry for the location and name of the JVM DLL. This information is located in a subkey of the HKEY_LOCAL_MACHINE root key. This subkey is SOFTWARE\\JavaSoft\\Java Runtime Environment\\1.2 and contains a RuntimeLib entry. The value associated with this entry is the location and name of the JVM DLL.

Finally, let's examine te.java. Figure 2 shows te's main window.

This window consists of a single File menu (with Load, Save, and Quit options), a text area for viewing and editing the contents of a file, and a pair of status lines (one line identifies currently loaded or saved file while the other line displays error messages).

Before concluding, let's summarize what you need to do in order to run the text editor on your computer.

• Install the JRE
• Place te.exe and te.class in the same directory
• Set the CLASSPATH environment variable (a Win32 environment variable that the JVM uses to locate class files) to point to the directory containing te.class

if (RegOpenKeyEx (HKEY_LOCAL_MACHINE,
                  "SOFTWARE\\JavaSoft\\Java Runtime Environment\\1.4",
                  0,
                  KEY_ALL_ACCESS,
                  &key) != ERROR_SUCCESS)

While the Win32-Java hybrid approach won't be useful in all situations, it's a good little hack to keep your Java skills relevant and your Java code running in a Windows environment. With a little practice, this alternative method can become a valuable tactic for getting through the turbulence that now has the Java community rattled with uncertainty.

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