IBM User Guide for Java V7 on Windows > Reference > Command-line options > JVM command-line options

-Xzero

Enables reduction of the memory footprint of the Java™ runtime environment when concurrently running multiple Java invocations.

-Xzero[:<option>]

-Xzero might not be appropriate for all types of applications because it changes the implementation of java.util.ZipFile, which might cause extra memory usage. -Xzero includes the optional parameters:

• j9zip - enables the j9zip sub option
• noj9zip - disables the j9zip sub option
• sharezip - enables the sharezip sub option
• nosharezip - disables the sharezip sub option
• sharebootzip - enables the sharebootzip sub option
• nosharebootzip - disables the sharebootzip sub option
• none - disables all sub options
• describe - prints the sub options in effect

Because future versions might include more default options, -Xzero options are used to specify the sub options that you want to disable. By default, -Xzero enables j9zip and sharezip. A combination of j9zip and sharezip enables all .jar files to have shared caches:

• j9zip - uses a new java.util.ZipFile implementation. This suboption is not a requirement for sharezip; however, if j9zip is not enabled, only the bootstrap .jar files have shared caches.
• sharezip - puts the j9zip cache into shared memory. The j9zip cache is a map of zip entry names to file positions used to quickly find entries in the .zip file. You must enable -Xshareclasses to avoid a warning message. When using the sharezip suboption, note that this suboption allows every opened .zip file and .jar file to store the j9zip cache in shared memory, so you might fill the shared memory when opening multiple new .zip files and .jar files. The affected API is java.util.zip.ZipFile (superclass of java.util.jar.JarFile). The .zip and .jar files do not have to be on a class path.
• sharebootzip - enabled by default on all platforms. Puts the zip entry caches for bootstrap .jar files into the shared cache. A zip entry cache is a map of zip entry names to file positions, used to quickly find entries in the .zip file.

The system property com.ibm.zero.version is defined, and has a current value of 2. Although -Xzero is accepted on all platforms, support for the sub options varies by platform:

• -Xzero with the sharebootzip and nosharebootzip sub options are accepted on all platforms.
• -Xzero with all other sub options are available only on Windows x86-32 and Linux x86-32 platforms.

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Parent: JVM command-line options

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