About Mac OS Runtime for Java 2.1

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Introduction

Mac OS Runtime for Java (MRJ) 2.1 is Apple’s implementation of the Java Virtual Machine (JVM), based on Sun Microsystems’ Java 1.1.6 specification. MRJ allows you to run Java applications and applets. (Running applets also requires a Web browser, such as Microsoft Internet Explorer, or an applet viewer such as the Apple Applet Runner.)

MRJ 2.1 makes many improvements over Apple’s previous JVM, including greatly increased performance, improved reliability, and support for AppleScript and Sun’s JFC/Swing. MRJ 2.1 also runs more applications and applets than earlier versions.

For the latest developments in Java for the Macintosh, see Apple’s Java Web site at [1].

Configuring your Web browser

Mac OS versions 8.0 and later come with a copy of Internet Explorer configured to work with MRJ. If you’re using a different browser or if you got Internet Explorer from another source, you may need to configure it to use MRJ.

Note: Versions of Netscape Communicator/Navigator up to and including 4.5 use their own internal Java Virtual Machine and cannot be configured to use MRJ. Apple and Netscape are working together to develop a future version of Netscape Communicator/Navigator that will make use of MRJ. For more information on Netscape’s browsers, you can monitor their web site at [2].

To configure Internet Explorer to use MRJ, choose Preferences from the Edit menu. In the Java Options section, make sure Java is enabled and Apple MRJ is selected as the Java Virtual Machine. To make your changes take effect, quit the browser and open it again.

Minimum system requirements

  • Macintosh computer with a PowerPC processor
  • System 7.6.1 or later
  • 24 megabytes (MB) of RAM. For better performance, 32 MB of RAM is recommended, with virtual memory turned on and set to at least 33 MB. Installing more than 32 MB of RAM will greatly improve performance and increase the number of Java applets and applications that can run simultaneously.
  • At least 20 MB of free disk space
  • Using Java applets over the Internet requires Open Transport 1.1 or later and an active Internet connection.
  • You may experience improved performance if you have QuickTime 3.0 installed. QuickTime 3.0 is installed with Mac OS 8.5, or you can download it at [3].

Files installed with MRJ 2.1

In the Extensions folder (inside the System Folder)

  • MRJ Libraries folder, containing MRJ Lib, MRJ Symantec JITC, the MRJClasses folder and the lib folder.
  • MRJ Enabler extension (installed only on computers using Mac OS 8.1 or earlier)
  • Text Encoding Converter 1.4.2
  • Appearance Extension 1.0.3 (installed only on computers using Mac OS 7.6.1)

In the System Folder

  • A Text Encodings folder containing version 1.4.2 of the encodings

In the Control Panels folder (inside the System Folder)

  • Appearance control panel 1.0.3 (installed only on computers using Mac OS 7.6.1)

In the Preferences folder (inside the System Folder)

  • Appearance Preferences 1.0.3 (installed only on computers using Mac OS 7.6.1)

In the Apple Extras folder

  • Mac OS Runtime for Java folder

For International Users

The MRJ 2.1 Installer installs U.S. English versions of the Text Encoding Converter 1.4.2 and associated text encodings. On most computers, these files replace older versions of the same files. However, on some computers sold outside the United States (such as computers sold in France), the filenames of the existing Text Encoding Converter and associated text encodings have been changed. On these computers, the MRJ Installer cannot recognize and replace the older files and does not install the Text Encoding software.

If you have a non-U.S. computer with Text Encoding 1.3 or later installed, MRJ works but may experience some text handling errors that don’t occur on other computers.

If you have an earlier version of the Text Encoding software installed, an alert message appears during installation and tells you that your system software must be updated before MRJ can be installed.

Known issues

  • Secure Sockets: MRJ 2.1 does not support the Secure Sockets Layer interface (SSL), which allows applets to access Web pages via “https.”
  • Appearance Manager 1.0: If your system is using Appearance Manager 1.0 (which comes with Mac OS 8), you may see dialog boxes without borders or other visual inconsistencies. You should upgrade to Mac OS 8.1 or later. A free upgrade from 8.0 to 8.1 is available at Apple’s Web site. Go to [4] and search for "Software Updates".
  • Games and modifier keys: Some game applets use the Shift, Alt, and Control keys as game controllers. In some cases, these controls will not work as expected.
  • Apple Studio Display: If you have an Apple Studio Display (flat-panel monitor) and Mac OS 8.1 or earlier installed, you may see cosmetic inconsistencies in the Monitors & Sound control panel. You should update your Apple Displays software as soon as an update becomes available. To check on its availability, go to [5] and search for "Software Updates".
  • Yahoo games: Multi-user Yahoo games do not work correctly using Internet Explorer and MRJ 2.1. Apple, Microsoft, and Yahoo are working together to resolve this problem.
  • Low memory: When Java applications are running out of memory, MRJ may put up a blank window with no information in it and appear to crash. If this occurs, you can sometimes quit by selecting “Quit” from the Apple Menu (there is no Edit menu since Java did not start up properly). If several applications are running at the same time, quit unused applications to free up memory, or increase the amount of virtual memory in the Memory Control panel, and then try the application again. If this problem persists, you may need to add additional physical RAM.
  • Printing: If you use your browser’s Print command to print a Web page that contains an applet, the page will contain a blank area where the applet should be. If available, use the applet’s Print menu to print the page.

Miscellaneous notes

  • Java developers: MRJ is a runtime environment and does not include development tools. If you are interested in Java development, you need a Java development environment and the MRJ Software Development Kit (MRJ SDK). For more information, see the MRJ developer page at [6].
  • Apple Applet Runner: The Apple Applet Runner is now only available on the MRJ SDK. Apple Applet Runner 2.0, (which came with MRJ 2.0) is compatible with MRJ 2.1. For the latest version of Apple Applet Runner, download the MRJ SDK from the MRJ developer Web site at [7].
  • Swing: MRJ 2.1 is compatible with both Swing 1.0.3 and Swing 1.1. For more information or a copy of the Swing software, see the Sun Microsystems web site at [8]. To run Swing-based applets and applications, place the "swingall.jar" file in the MRJClasses folder, in the MRJ Libraries folder in the Extensions folder (inside the System Folder).

Warning: Java technology is not fault tolerant and is not designed, manufactured, or intended for use or resale for online control of equipment in nuclear facilities, aircraft navigation or communication systems, or air traffic control machines in which the failure of the Java technology or Mac OS Runtime for Java could lead directly to death, personal injury, or severe physical or environmental damage.


© 1999 Apple Computer. Inc. All rights reserved.

Apple, the Apple logo, AppleScript, Mac, Macintosh, and QuickTime are trademarks of Apple Computer, Inc., registered in the U.S. and other countries. PowerPC is a trademark of International Business Machines Corporation, used under license therefrom. Java and all Java-based trademarks and logos are trademarks or registered trademarks of Sun Microsystems, Inc. in the U.S. and other countries. Netscape Navigator is a trademark of Netscape Communications Corporation. Other product and company names mentioned herein may be trademarks of their respective companies.

Revised 3/16/99

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