Java on HP-UX 11i Frequently Asked Questions

Q: How can I exclude a method from HotSpot compilation?

A: Create a file in the home directory where the Java application will be started, name

it .hotspot_compiler and include entries describing the method(s) to exclude in the

form of:

exclude class_name method_name

for example:

exclude hpdocs/com/bean/PersistentBean addInnerPersistentFields

For more information on excluding methods, see the “HotSpot Technology Tools and

Commands” section of the HP-UX Programmer's Guide for Java 2 on the Business Support

Center at:

http://www.hp.com/go/hpux-java-docs.

Q: What is the maximum method code size for a Java class?

A: Currently, the JVM specification remains at 64K for max bytecode size of a method.

There are currently no plans to increase this by JavaSoft.

Q: What is the limit of the number of classes that can be loaded?

A: There is no limit to the number of classes that can be loaded other than memory.

Class definitions are loaded into the PermSpace by the class loader. When the PermSpace

fills up, and a Full GC is unable to free up space, you will begin to get

OutOfMemoryError exceptions. You can make the PermSpace larger by using

-XX:MaxPermSize=<value>. The default is 64MB. Prior to making a change, it may

be a good idea to run with -Xverbosegc and use HPjtune to observe the use of the

Permanent space. Also see the HP-UX Programmer's Guide for Java 2 on the Business

Support Center at:

http://www.hp.com/go/hpux-java-docs.

Q: What mechanism causes classes to be unloaded by the JVM?

A: When a class is referenced (i.e. with a new statement) for the first time, the class

definition is loaded using either the default class loader or a custom one if you've

defined one. The class definition is stored in an area of the Java heap called the Perm

Space. All allocated instances of that class definition have a reference back to the

reference stored in the Perm Space. When there are no longer any class instances that

reference that class definition, the definition becomes a candidate for collection. The

next time a full garbage collection takes place, all class definitions in the Perm Space

that aren't referenced by any actual instances will be cleaned up or unloaded. One way

to trigger a full garbage collection is if the Perm Space fills up. This can be seen by

watching the output of -Xverbosegc and looking for the cause of GC.