IBM 32-bit Runtime Environment for Windows, Java 2 Technology Edition, Version 1.4.2

User Guide


Copyright information

Note: Before using this information and the product it supports, be sure to read the general information under Notices.

This edition of the User Guide applies to the IBM 32-bit Runtime Environment for Windows, Java 2 Technology Edition, Version 1.4.2, and to all subsequent releases, modifications, and service refreshes, until otherwise indicated in new editions.

(c) Copyright Sun Microsystems, Inc. 1997, 2003, 901 San Antonio Rd., Palo Alto, CA 94303 USA. All rights reserved.

(c) Copyright International Business Machines Corporation, 1999, 2006. All rights reserved.

U.S. Government Users Restricted Rights - Use, duplication or disclosure restricted by GSA ADP Schedule Contract with IBM Corp.

Preface

The IBM(R) 32-bit Runtime Environment for Windows(R), Java(TM) 2 Technology Edition, Version 1.4.2 contains the Java Virtual Machine (JVM), core Sun Microsystems Java classes, and supporting files. The Runtime Environment does not contain all the classes that are found in the SDK package.

The User Guide provides general information about the Runtime Environment and specific information about any differences in the IBM implementation of the Runtime Environment compared with the Sun implementation. Read this User Guide in conjunction with the more extensive documentation on the Sun Web site: http://java.sun.com.

The Runtime Environment is supported on the following products:

|Note that IPv6 is supported only on Windows |XP and Windows Server 2003.

The IBM JVM Diagnostics Guide provides more detailed information about the IBM JVM.

Note that the Runtime Environment for Windows is a subset of the SDK and enables you only to run Java applications. If you have installed the SDK, the Runtime Environment is included.

The terms "Runtime Environment" and "Java Virtual Machine" are used interchangeably throughout this User Guide.

Technical changes made to this User Guide for Version 1.4.2, other than minor or obvious ones such as updating "1.4.1" to "1.4.2", are indicated in red when viewing in HTML or in a color-printed copy and by vertical bars to the left of the changes.

Contents

Copyright information
Preface
Using the Runtime Environment
Obtaining the IBM build and version number
The just-in-time (JIT) compiler
Launching a Java application
Summary of commands
Options
Globalization of the java command
Working with classpaths
Executing a Java file automatically
Working with the bootclasspath
Specifying garbage collection policy
| |
Implementing the Connection Handler Pool for RMI
How the JVM processes signals
Signals used by the JVM
Linking a native code driver to the signal-chaining library
Using the Java Plug-in
Supported browsers
Using DBCS parameters
Running Java applications with native assistive technologies
Using Web Start
Working with an Input Method Editor
Known limitations
Any comments on this User Guide?
Notices
Trademarks

Using the Runtime Environment

There is no guarantee that 1.4.2-compiled classes will work on pre-1.4.0 Runtime Environment releases.

Obtaining the IBM build and version number

To obtain the IBM build and version number, at a command prompt type:

java -version

The just-in-time (JIT) compiler

The just-in-time (JIT) compiler (jitc.dll) dynamically generates machine code for frequently used bytecode sequences in Java applications and applets while they are running.

The Runtime Environment for Windows includes the JIT (jitc.dll), which is enabled by default. You can disable the JIT to help isolate a problem with a Java application, an applet, or the compiler itself.

There are two ways to disable the JIT:

To enable the JIT, type at a command prompt:

    set JAVA_COMPILER=jitc

To verify whether or not the JIT is enabled, type at a command prompt:

    java -version

If the JIT is in use, a message is displayed that includes:

(JIT enabled: jitc)

If the JIT is not in use, a message is displayed that includes:

(JIT disabled)

Launching a Java application

The java tool launches a Java application.

The JVM searches for the startup class, and other classes that are used, in three sets of locations: the bootstrap classpath, the installed extensions, and the user classpath. Arguments after the class name or JAR file name are passed to the main function.

The javaw command is identical to java, except that javaw has no associated console window. Use javaw when you do not want a command prompt window to appear. The javaw launcher displays a dialog box with error information if a launch fails.

Summary of commands

The java and javaw command have the following syntax:

java [ options ] class [ arguments ... ]
java [ options ] -jar file.jar [ arguments ... ]
javaw [ options ] class [ arguments ... ]
javaw [ options ] -jar file.jar [ arguments ... ]

Items that are within brackets are optional.

options
Command-line options.
class
Name of the class to invoke.
file.jar
Name of the jar file to invoke. It is used only with -jar.
argument
Argument passed to the main function.

If the -jar option is specified, the named .jar file contains class and resource files for the application, with the startup class indicated by the Main-Class manifest header.

From Version 1.4.2 Service Refresh 4, using the -jar command-line option will make the .jar file the source of all user classes; all other user CLASSPATH settings will be ignored.

To be able to use a .jar file with other CLASSPATH settings, add the .jar file to the CLASSPATH as above, and specify the startup class manually.

Options

The launcher has a set of standard options that are supported on the current runtime environment and will be supported in future releases. In addition, there is a set of nonstandard options.

Standard options

Non-standard options

The -X options listed below are a subset of the available ones. They are nonstandard and subject to change without notice.

Globalization of the java command

The java command and other java launcher commands (such as javaw) allow a class name to be specified as any character that is in the character set of the current locale.

You can specify any Unicode character in the class name and arguments by using java escape sequences. To do this, you must specify -Xargencoding. To specify a Unicode character, use escape sequences in the form \u####, where # is a hexadecimal digit (0 through 9, A through F).

To specify that the class name and command arguments are in UTF8 or ISO8859_1 encoding, use -Xargencoding:utf8 and -Xargencoding:latin.

In the Runtime Environment, if you are using a non-English locale, the java and javaw commands give translated output messages. These messages are different from those that were in the 1.3.1 version and also differ based on the locale in which Java is running. The detailed error descriptions and other debug information that is returned by java is in English. Debug information that is returned during initialization is shown in brackets.

Working with classpaths

In the Runtime Environment, you can specify a class name as a complete file name including a full path and the .class extension. In previous versions of the SDK, you could specify only the class that was relative to the CLASSPATH, and the .class extension was not allowed. Use of the complete file name permits you to launch a java application from your desktop or file launcher. If you specify a .class file with path and extension, the specified path is put into the CLASSPATH. For example, the command java c:\myapp\thisapp.class is equivalent to specifying java -classpath c:\myapp thisapp.

From Version 1.4.2 Service Refresh 4, using the -jar command-line option will disable the use of a CLASSPATH.

Executing a Java file automatically

To set a java class or jar file to execute automatically from the file use Tools->Folder Options->File Type option of Windows Explorer. Alternatively, at a command prompt type:

assoc .class=javaclass 
ftype javaclass=C:\Program Files\IBM\Java142\jre\bin\java.exe %l %*
Notes:
  1. The %l is the letter l and not the number 1.
  2. If your Java is installed in a directory other than C:\Program Files\IBM\Java142\, substitute your directory.

Working with the bootclasspath

You can set the system property ibm.jvm.bootclasspath by using the -D option that is described in Launching a Java application. The value of this property is used as an additional search path, which is inserted between any value that is defined by -Xbootclasspath/p: and the bootstrap classpath. The bootstrap classpath is either the default, or that is defined using the -Xbootclasspath: option.

Do not deploy applications that use the -Xbootclasspath: or -Xbootclasspath/p: option to override a class in core.jar, graphics.jar, server.jar, security.jar, xml.jar, tools.jar, or charsets.jar, because such a deployment would contravene the Java 2 Runtime Environment binary code license.

Specifying garbage collection policy

The -Xgcpolicy JVM runtime option specifies garbage collection policy.

-Xgcpolicy takes the values optthruput (the default) or optavgpause. The option controls garbage collector behavior, making tradeoffs between throughput of the application and overall system and the pause times that are caused by garbage collection.

The format of the option and its values is:

-Xgcpolicy:optthruput

-Xgcpolicy:optavgpause

Pause time

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. Because 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.

Pause time reduction

The optavgpause option substantially reduces the time that is spent in these garbage collection pauses, in addition to limiting the effect of increasing heap size on the length of the garbage collection pause. This option is particularly relevant to configurations that have large heaps. The pause times are reduced by performing some garbage collection activities that are concurrent with normal program execution. With the reduced pause time, you might experience some reduction of application throughput, which varies from application to application.

Environments with very full heaps

If the Java heap becomes nearly full, and very little garbage is to be reclaimed, requests for new objects might not be satisfied quickly because no space is 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 OutofMemory exception, which results in JVM termination if the exception is not caught and handled. At this point the JVM will produce two diagnostic files: a Heapdump and a Javadump. These are detailed in the Diagnostics Guide for Java v1.4.2 and can be used to determine what caused the high occupancy of the Java heap. The Diagnostics Guide is on developerWorks, at: http://www-106.ibm.com/developerworks/java/jdk/diagnosis/. In these conditions, you are recommended either to increase the heap size by using the -Xmx option, or to reduce the number of application objects in use.

Further information about garbage collection

For more detailed information about garbage collection, see:

http://www.ibm.com/developerworks/ibm/library/i-garbage1/

http://www.ibm.com/developerworks/ibm/library/i-garbage2/

http://www.ibm.com/developerworks/ibm/library/i-garbage3/

| | |

Implementing the Connection Handler Pool for RMI

|

Thread pooling for RMI Connection Handlers is not enabled |by default.

|

To enable the connection pooling implemented at the RMI TCPTransport level, |set the option

|
-Dsun.rmi.transport.tcp.connectionPool=true (or any non-null value) 
|

This version of the Runtime Environment does not have any setting that |you can use to limit the number of threads in the connection pool.

How the JVM processes signals

When a signal is raised that is of interest to the JVM, a signal handler is called. This signal handler determines whether it has been called for a Java or non-Java thread. If the signal is for a Java thread, the JVM takes control of the signal handling. If the signal is for a non-Java thread, and the application that installed the JVM had previously installed its own handler for the signal, control is given to that handler. Otherwise, the signal is ignored (whether or not this is not the signal's default action). The exception to this rule is on Windows, where for a signal generated externally (for example, when you enter CTRL-C or CTRL-BREAK) a new thread is created to execute the signal handler. In this case, the JVM signal handler assumes that the signal is for the JVM.

For exception and error signals the JVM either:

For information about how to write a launcher that specifies the above hooks, see: http://www-106.ibm.com/developerworks/java/library/i-signalhandling/. This item was written for Java V1.3.1, but applies also to later versions.

For interrupt signals, the JVM also enters a controlled shutdown sequence, but this time it is treated as a normal termination that:

The shutdown is identical to the shutdown initiated by a call to the Java method System.exit().

Other signals that are used by the JVM are for internal control purposes and do not cause it to terminate. The only control signal of interest is SIGBREAK, which causes a Javadump to be generated.

Signals used by the JVM

Table 1 below shows the signals that are used by the JVM. The signals have been grouped in the table by type or use, as follows:

Table 1. Signals used by the JVM
Signal Name Signal type Description Disabled by -Xrs
SIGSEGV Exception Incorrect access to memory (write to inaccessible memory) No
SIGILL Exception Illegal instruction (attempt to invoke an unknown machine instruction) No
SIGFPE Exception Floating point exception (divide by zero) No
SIGABRT Error Abnormal termination. The JVM raises this signal whenever it detects a JVM fault. Yes
SIGINT Interrupt Interactive attention (CTRL-C). JVM exits normally. Yes
SIGTERM Interrupt Termination request. JVM will exit normally. Yes
SIGBREAK Control A break signal from a terminal. JVM uses this for taking Javadumps. Yes

Use the -Xrs (reduce signal usage) option to prevent the JVM from handling most signals. For more information, see Sun's Java application launcher page at http://java.sun.com/j2se/1.4.2/docs/tooldocs/windows/java.html.

Signals 2 (SIGINT), 4 (SIGILL), 6 (SIGABRT), 8 (SIGFPE), 11 (SIGSEGV), and 15 (SIGTERM) cause the JVM to shut down; therefore, an application signal handler should not attempt to recover from these unless it no longer requires the services of the JVM.

Linking a native code driver to the signal-chaining library

The Runtime Environment contains a signal-chaining facility. Signal-chaining enables the JVM to interoperate more efficiently with native code that installs its own signal handlers.

The signal-chaining facility enables an application to link and load the shared library jsig.dll before msvcrt.dll. The jsig.dll library ensures that calls to signal() are intercepted so that their handlers do not replace the JVM's signal handlers. Instead, these calls save the new signal handlers, or "chain" them behind the handlers that are installed by the JVM. Later, when any of these signals are raised and found not to be targeted at the JVM, the preinstalled handlers are invoked.

To use jsig.dll, link it with the application that creates or embeds a JVM.

Using the Java Plug-in

The Java Plug-in is a Web browser plug-in. If you use the Java Plug-in, you can bypass your Web browser's default JVM and use instead a Runtime Environment for running applets or beans in the browser.

The Java Plug-in is documented by Sun at: http://java.sun.com/j2se/1.4.2/docs/guide/plugin/developer_guide/.

Supported browsers

|Table 2. Browsers supported by the Java Plug-in
|Operating System |Internet Explorer default versions |Internet Explorer supported versions |Netscape default versions |Netscape supported versions |Mozilla supported versions
|Windows 98 |5.0 (Second Edition) |5.5 SP2, 6.0, 7.0 | |4.78, 7.1 |1.7, Firefox 1.0.x
|Windows ME |5.5 |5.5 SP2, 6.0, 7.0 | |4.78, 7.1 |1.7, Firefox 1.0.x
|Windows 2000 |5.01 |5.5 SP2, 6.0, 7.0 | |4.78, 7.1 |1.7, Firefox 1.0.x
|Windows XP |6.0 |6.0, 7.0 | |4.78, 7.1 |1.7, Firefox 1.0.x
|Windows Server 2003 |6.0 |6.0, 7.0 | |4.78, 7.1 |1.7, Firefox 1.0.x

Using DBCS parameters

The Java Plug-in supports double-byte characters (for example Chinese Traditional BIG-5, Korean, Japanese) as parameters for the tags <APPLET>, <OBJECT>, and <EMBED>. You must select the correct character encoding for your HTML document so that the Java Plug-in can parse the parameter. Specify character encoding for your HTML document by using the <META> tag in the <HEAD> section like this:

<meta http-equiv="Content-Type" content="text/html; charset=big5">

This example tells the browser to use the Chinese BIG-5 character encoding to parse the HTML file using. All the parameters are passed to the Java Plug-in correctly. However, some of the older versions of browsers might not understand this tag correctly. In this case, you can force the browser to ignore this tag, but you might have to change the encoding manually.

You can specify which encoding you want to use to parse the HTML file:

Running Java applications with native assistive technologies

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 support 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. A copy of jaccess.jar is shipped in the appropriate directory for use with JawBridge. A copy of jaccess.jar is shipped in the appropriate directory for use with JawBridge.

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:

assistive_technologies=com.sun.java.accessibility.AccessBridge, 
JawBridge

Comment out the line with a leading # to deactivate both bridges. This Web site tells you how to how to download the Java Access Bridge:

http://java.sun.com/products/jfc/accessibility.html

Using Web Start

Java Web Start is a way of deploying Java technology-based applications. It connects the computer and the Internet and allows the user to launch and manage applications directly from the Web. Java Web Start provides one-click activation of applications, and ensures that you are always running the latest version, eliminating installation or upgrade procedures. Often, distributing software across the Web requires you to find the installer on the Web, download the installer, locate the installer, and execute the installer. After the installer is executed, it prompts for installation directories and installation options such as full, typical, or minimum. This can be a time-consuming and complicated task that must be repeated for each new version of the software.

In contrast, Web-deployed applications, such as your HTML-based e-mail client and calendar, are straightforward to install and use. The Web browser has automated the process. There are no complicated download, setup, and configuration steps, and you are guaranteed to be running the latest version. Java Web Start provides the same benefits to full-featured applications.

For information on the browsers that support Web Start see the section Supported browsers.

For more information about Web Start, see: http://java.sun.com/products/javawebstart and for more documentation, see: http://java.sun.com/j2se/1.4.2/docs/guide/jws/index.html.

Working with an Input Method Editor

When working with an Input Method Editor (IME), you are advised that character composition should be completed and the candidate selected before using the workspace for any other operation.

Known limitations

Note the following limitations about this runtime environment:

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Notices

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