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Question: Do you know about "Full Speed
Debugging" and "HotSwap" Class File Replacement in Java Debugger since v.1.4.1?
Answer: Part 1. Full Speed Debugging
The Java HotSpot[TM] virtual machine now uses "full-speed debugging". In the
previous version of HotSpot, when debugging was enabled, the program executed
using only the interpreter. Now, the full performance advantage of HotSpot
Technology is available to programs running with debugging enabled. The improved
performance allows long running programs to be more easily debugged. It also
allows testing to proceed at full speed and the launch of a
debugger to occur on an exception:
Setting a breakpoint only inhibits compilation (full speed execution) for the
method containing the breakpoint. Execution reverts to the interpreter during
some debug operations such as single-stepping and when method entry/exit or
watchpoints are set.
As of version 1.4.1, full-speed debugging is available with both the Java
HotSpot Client Vm (default) and Java HotSpot Server VM (invoked with the -server
command-line flag). In the Java 2 SDK v1.4.0, full-speed debugging was available
only with the Java HotSpot Client VM.
This tip is based on release info for the version 1.4.1 family of the Java 2
Part 2 will be found in my next newsletter
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