=== [ The
Java FAQ Daily Tips, weekly publication ]
===
| Issue
No: 177
5 August
2003 |
| 14019 subscribers
|
Foreword: Excuse me for
possible mistakes. English is not native language for me.
In this issue:
Hello dear friends!
In one of my last newsletters was the answer to the
question:
Why wait(), sleep(), notify(), notifyAll()
must be inside a synchronized block, otherwise it throws
java.lang.IllegalMonitorStateException: current thread not owner.
see newsletter No 175, tip 2, July 22
Harald M. Mueller from
Germany corrected me:
"This is not true for sleep(). However, sleep() can
throw an
InterruptedException. It is, in many cases, ok to write
try
{
Thread.sleep(...);
} catch (InterruptedException
ex) {
// empty - ignore the
exception
}
THIS IS THE ONLY SITUATION WHERE AN EXCEPTION MAY BE
IGNORED!!! In all other
catch blocks, either
* rethrow an exception
*
show the problem in a GUI dialog
* crash the program
Writing an exception
to stdout or stderr with ex.printStacktrace() is NOT OK!!
...
Regards
Harald M. Mueller Germany "
Thanks for correction. Please always correct me
if I am wrong!
--
John
Question: When does garbage collection performance
matter to the user?
Answer: For many applications it doesn't. That is, the
application can perform within its specifications in the presence of garbage
collection with pauses of modest frequency and duration. An example where this
is not the case (when the default collector is used) would be a large
application that scales well to large number of threads, processors, sockets,
and a large amount of memory.
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Question: What is young generation in GC(Garbage
Collector)?
Answer: In the J2SE platform version 1.4.1 two new
garbage collectors were introduced to make a total of four garbage collectors
from which to choose.
Beginning with the J2SE platform, version 1.2, the
virtual machine incorporated a number of different garbage collection algorithms
that are combined using generational collection. While naive garbage collection
examines every live object in the heap, generational collection exploits several
empirically observed properties of most applications to avoid extra work.
The default collector in
HotSpot has two generations: the young generation and the tenured generation.
Most allocations are done in the young generation. The young generation is
optimized for objects that have a short lifetime relative to the interval
between collections. Objects that survive several collections in the young
generation are moved to the tenured generation. The young generation is
typically smaller and is collected more often. The tenured generation is
typically larger and collected less often.
The young generation
collector is a copying collector. The young generation is divided into 3 spaces:
eden-space, to-space, and from-space. Allocations are done from eden-space and
from-space. When those are full a young generation is collection is done. The
expectation is that most of the objects are garbage and any surviving objects
can be copied to to-space. If there are more surviving objects than can fit into
to-space, the remaining objects are copied into the tenured generation. There is
an option to collect the young generation in parallel.
The tenured generation is
collected with a mark-sweep-compact collection. There is an option to collect
the tenured generation concurrently.
This tip is based on FAQ
about Garbage Collection in the HotSpot Java Virtual Machine
http://java.sun.com/docs/hotspot/gc1.4.2/faq.html
and
article "Tuning Garbage Collection with the 1.4.2 Java Virtual Machine"
http://java.sun.com/docs/hotspot/gc1.4.2/
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Question: Why SUN does not introduce dynamic policies
(for security)?
Answer: Support for dynamic policies has been added.
In Java 2 SDK releases prior to version 1.4, classes were statically bound with
permissions by querying security policy during class loading. The lifetime of
this binding was scoped by the lifetime of the class loader. In version 1.4 this
binding is now deferred until needed by a security check. The lifetime of the
binding is now scoped by the lifetime of the security policy.
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Hi,
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Hello,
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In a JTree i show a JPopup if i clicked with right mousebutton.
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