[ The Java FAQ Daily Tips, weekly publication ]
Foreword: Excuse me for
possible mistakes. English is not native language for me.
In this issue:
Hello dear friends!
Question: The class Robot was introduced in Java
version 1.3 and belongs to awt (java.awt.Robot). Why? I got an impression that
all new GUI features come to Swing and Robot class is GUI related
Answer: The reason is simple: The Swing toolkit is a
fully-featured UI component library implemented entirely in the Java programming
language. The Robot class is used to generate native system input events for the
purposes of test automation, self-running demos, and other applications where
control of the mouse and keyboard is needed. The primary purpose of Robot is to
facilitate automated testing of Java platform implementations.
Using the class to generate
input events differs from posting events to the AWT event queue or AWT
components in that the events are generated in the platform's native input
queue. For example, Robot.mouseMove will actually move the mouse cursor instead
of just generating mouse move events.
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Question: What is jvmstat?
Answer: The jvmstat technology adds light weight
performance and configuration instrumentation to the HotSpot JVM and provides a
set of monitoring APIs and tools for monitoring the performance of the HotSpot
JVM in production environments. The instrumentation is designed such that it is
'always on', yet has negligible performance impact. The monitoring interfaces
added to the HotSpot JVM are proprietary and may or may not be supported in
future versions of the HotSpot JVM.
Tools include a general
purpose command line tool called jvmstat, a java process list tool called jvmps,
and a generational heap visualization tool called visualgc. Remote monitoring is
supported via an RMI server application.
The instrumented HotSpot JVM
shipped with J2SE 1.4.1 as a technology preview. The instrumentation is disabled
by default, but can be easily enabled through a command line argument. The tools
included with this distribution can only monitor Java applications running on
the HotSpot 1.4.1 JVM as distributed with Sun's J2SE 1.4.1
The jvmstat feature includes
a number of tools:
jvmstat - A tool to sample
and log instrumentation
jvmps - A tool providing a
simple Java process listing
visualgc - A tool to
graphically display instrumentation
perfagent - A server
providing remote access to instrumentation
tip is based on
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Question: What type of garbage collection does a
Answer: An explicit request to do a garbage collection
does a full collection (both young generation and tenured generation). A full
collection is always done with the application paused for the duration of the
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