Note: Before using this information and the product it supports, be sure to read the general information under Notices.
This edition of the README applies to IBM Developer Kit for Windows, Java 2 Technology Edition, Version 1.3.1, 32-bit version and to all subsequent releases and modifications until otherwise indicated in new editions.
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This README file provides information about the Runtime Environment package provided with IBM(R) Developer Kit for Windows(R), Java(TM) 2 Technology Edition, Version 1.3.1, 32-bit version. Use this README file if you plan to distribute the Runtime Environment with your product.
The Runtime Environment is supported on the following products:
The Runtime Environment contains the Java Virtual Machine (JVM), Sun Microsystems Java classes, and supporting files. The Runtime Environment does not contain all the classes found in the Developer Kit package.
The Runtime Environment includes .dll files plus classes to support a Java program at runtime. The Runtime Environment does not include any of the development tools, such as appletviewer or javac, or classes that would pertain only to a development system.
See Redistribution requirements for information about files that must be redistributed with Java programs.
The JIT compiler generates machine code dynamically for frequently used bytecode sequences in a Java application or applet during execution. The JIT compiler (jitc.dll) is enabled by default.
You can disable the JIT to help in the isolation of a problem with a Java application, an applet, or the compiler itself.
There are two ways to disable the JIT:
set JAVA_COMPILER=NONE
On Windows NT, Windows 2000, and Windows XP, you can also permanently set JAVA_COMPILER from the Environment settings of the System properties. (For Windows NT, select the Control Panel, and select System and then select Environment. For Windows 2000 and Windows XP, select the Control Panel and System, and on the Advanced tab select Environment Variables).
java -Djava.compiler=NONE myapp
To enable the JIT, type the following at a command prompt:
set JAVA_COMPILER=jitc
To verify whether or not the JIT is enabled, type the following at a command prompt:
java -version
If the JIT is in use, a message is displayed that includes the following:
JIT enabled: jitc
If the JIT is not in use, the following message is displayed:
JIT disabled
The IBM build and version number can be obtained by typing the following at a command prompt:
java -version
To run a Java application, type the following at a command prompt:
java classname
where classname is the name of the Java class file (Java
application) that you want to run. For information about
parameters you can use when invoking the java tool, see
The Java Runtime Interpreter.
Note: If you did not install the Runtime Environment as the system JVM, you must first set the path to include the appropriate directories. To update the path, type the following at a command prompt:
set path=javadir\jre\bin;%path%
where javadir is the directory where the
Runtime Environment package is installed. By
default, this directory is
When you redistribute the Runtime Environment, you are required to include files from the following package:
For specific information about the files that must be redistributed, see the license agreement that accompanies this product.
The term required means that licensees who distribute the runtime must include those files with their program, whether or not their program ever uses those files.
The Runtime Environment includes the \bin and \lib directories and their subdirectories. These two directories and their subdirectories must reside in the same directory. The bin directory contains executable files and native libraries. The lib directory contains the classes and property files.
All files in the bin and lib directories are required for redistribution.
Note: The native code C runtime library, msvcrt.dll, is located in the Windows system directory. Be sure that file is in your Windows system directory. The location of this directory varies on different operating systems, but is usually:
The java tool invokes the Java Runtime Interpreter for executing Java applications. The syntax for starting the java tool is as follows:
java [-options] classname <args>
The classname argument is the name of the class file to
be executed. Any arguments to be passed to the class
must be placed after the classname on the command
line.
java -jar [-options] jarfile <args>
The jarfile argument is the name of the jar file to
be executed. Any arguments to be passed to the jar file
must be placed after the jarfile on the command
line.
An alternative for the java tool, javaw, is available. The javaw tool is identical to the java tool, except that it does not invoke a console window. The syntax for starting the javaw tool is as follows:
javaw [options] classname <args>
Options for the java tool are as follows:
The -X options are nonstandard and subject to change without notice.
The Sun Web page contains a "Hello World" example. The example demonstrates how to create a simple Java application that runs on and is bundled with the Java Runtime Environment. The Sun Web site is http://java.sun.com and you can find the "Hello World" example by searching on "Hello World" and "Notes for Developers".
The example shows how to make a simple, seamless transition from developing an application with a Developer Kit to deploying it with the Runtime Environment.
In your product you must provide a way to:
If you redistribute the Runtime Environment, you must make sure that your installation procedure does not overwrite an existing installation (unless the existing Java Runtime Environment is an older version).
The preferred approach is to take the files contained in the redistributable Runtime Environment zip file, ibm-jre-n131p-win32-x86.zip, and install them in the same directory structure. Be sure to include all the files in the bin and lib directories and their subdirectories. These directories are described in Redistribution requirements. The Runtime Environment software can only be redistributed if all these files are included. In effect, when you ship your application, it has its own copy of the Runtime Environment.
If you use this approach, do not try to emulate the installation steps performed by the Runtime Environment installer.
Note: When you install the Runtime Environment, you must record program information in the Windows Registry, as follows:
| Java2 Runtime Environment/1.3.1/JavaHome | root dir of java\jre |
| Java2 Runtime Environment/1.3.1/JavaRuntimeLib | root dir of java\jre\bin\classic\jvm.dll |
| Java2 Runtime Environment/1.3.1/Microversion | 0 |
| Java Plug-in/1.3.1/JavaHome | root dir of java\jre |
| Java Plug-in/1.3.1/JavaRuntimeLib | root dir of java\jre\bin\classic\jvm.dll |
| Key name | Key value |
| Lucida Sans Typewriter Regular (TrueType) | LucidaTypewriterRegular.ttf |
| Lucida Bright Demibold Italic (TrueType) | LucidaBrightDemiItalic.ttf |
| Lucida Bright Italic (TrueType) | LucidaBrightItalic.ttf |
| Lucida Bright Regular (TrueType) | LucidaBrightRegular.ttf |
| Lucida Sans Demibold (TrueType) | LucidaSansDemiBold.ttf |
| Lucida Sans Demibold Oblique (TrueType) | LucidaSansDemiOblique.ttf |
| Lucida Sans Oblique (TrueType) | LucidaSansOblique.ttf |
| Lucida Sans Regular (TrueType) | LucidaSansRegular.ttf |
| Lucida Sans Typewriter Bold (TrueType) | LucidaTypewriterBold.ttf |
| Lucida Sans Typewriter Bold Oblique (TrueType) | LucidaTypewriterBoldOblique.ttf |
| Lucida Sans Typewriter Oblique (TrueType) | LucidaTypewriterOblique.ttf |
| Lucida Bright Demibold (TrueType) | LucidaBrightDemiBold.ttf |
An example of the full path for a key value is:
This Developer Kit introduces the -Xgcpolicy JVM runtime option for specifying garbage collection policy.
-Xgcpolicy takes two values, optthruput (the default) and optavgpause. The option controls garbage collector behavior, making tradeoffs between throughput of the application and overall system and the pause times caused by garbage collection.
The format of the option and its values is:
-Xgcpolicy:optthruputand
-Xgcpolicy:optavgpause
When an application's attempt to create an object cannot be satisfied immediately from the available space in the heap, the garbage collector is responsible for identifying unreferenced objects (garbage), deleting them, and returning the heap to a state in which the immediate and subsequent allocation requests can be satisfied quickly. Such garbage collection cycles introduce occasional unexpected pauses in the execution of application code. As applications grow in size and complexity, and heaps become correspondingly larger, this garbage collection pause time tends to grow in size and significance. The default garbage collection value, optthruput, delivers very high throughput to applications, but at the cost of these occasional pauses, which can vary from a few milliseconds to many seconds, depending on the size of the heap and the quantity of garbage.
The optavgpause value substantially reduces the time spent in these garbage collection pauses, as well as limiting the effect of increasing heap size on the length of the garbage collection pause. This is particularly relevant to configurations with large heaps. (Consider a heap as large when it is at least 1 GB.) The pause times are reduced by overlapping garbage collection activities with normal program execution. This overlapping results in a small reduction to application throughput.
If the Java heap becomes nearly full, and there is very little garbage to be reclaimed, requests for new objects might not be satisfied quickly because there is no space immediately available. If the heap is operated at near-full capacity, application performance might suffer regardless of which of the above options is used; and, if requests for more heap space continue to be made, the application receives an Out of Memory exception, which results in JVM termination if the exception is not caught and handled. In these situations, you are recommended either to increase the heap size using the -Xmx option or to reduce the number of application objects in use.
For information on heap size tuning and the implications of garbage collection for application performance, see:
Sun provides the Java Access Bridge to give native Windows assistive technologies, such as screen readers, access to the Java Accessibility support in a Java application. These native Windows assistive technologies must have been written to make calls to the Java Access Bridge.
The Java Access Bridge available from Sun includes an installer, which places five files in the correct directories: access-bridge.jar, jaccess.jar, accessibility.properties, JavaAccessBridge.dll and WindowsAccessBridge.dll.
If you have already installed the IBM Accessibility Bridge (JawBridge), which allows the Windows 2000 Magnifier to function with Swing applications, and you want it to run at the same time as the Java Access Bridge, edit the line in the accessibility.properties file to read:
# to deactivate both bridges.
This Web site tells you how to how to download the Java Access Bridge:
Each property file contains comments that describe what the file is useful for and how to modify it.
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