This article discusses incremental compaction, a new feature in the memory management component of IBM JDK 1.4.0. Incremental compaction is a way of spreading compaction work across different garbage collection cycles, thereby reducing pause times. The authors discuss the need for incremental compaction, the compaction phases at a high level, and some runtime parameters. They also explain how to interpret changes in the verbosegc output.
Version: n/a Platform(s): n/a Updated: Wed Jun 25 2003
Love or hate it, static type checking can make code more robust. Programming languages are moving away from static type checking, but it is too powerful a debug resource to abandon. Static type checking can be one of the key weapons in a powerful arsenal against introducing and for detecting bugs. This article explains why we should be glad that the Java language supports it, and discusses how it can be made even better.
Every Java programmer should be aware of the problem of code pages vs. Java Unicode. This article describes some pitfalls to avoid with code page and Unicode conversions and provides example fixes for the problems. Armed with this informaion, you should be able to create applications that are more truly platform and code page independent.
Version: n/a Platform(s): n/a Updated: Mon Feb 11 2002
Learn the pros and cons of generating native code from Java source. This article includes the
basics of code compilation, including a brief overview of why many developers are employing Java
native compilers for their applications.
Version: n/a Platform(s): n/a Updated: Wed Jan 30 2002
One of the most important features of the Java language is support for multithreaded (also called concurrent) programming. This tutorial introduces you to the proper use of multiple threads in a Java program, using sample programs to illustrate these concepts. Before taking this course, you should have a general knowledge of Java programming; the context and level of knowledge used in this tutorial is the equivalent of an undergraduate operating systems course.
Version: n/a Platform(s): n/a Updated: Wed Oct 31 2001
The ThreadLocal class appeared with little fanfare in version 1.2 of the Java platform. While support for thread-local variables has long been a part of many threading facilities, such as the Posix pthreads facility, the initial design of the Java Threads API lacked this useful feature. Further, the initial implementation was quite inefficient. For these reasons, ThreadLocal gets relatively little attention, but it can be very handy for simplifying the development of thread-safe concurrent programs. This article examines ThreadLocal and offers tips for exploiting its power.
Version: n/a Platform(s): n/a Updated: Wed Oct 17 2001
The addition of the java.util.prefs package to Java 1.4 (through JSR 10) lets you manipulate user preference data and configuration data by providing you with access to an implementation-specific registry (for example, the Windows Registry on Windows platforms). This article introduces you to the Preferences class and walks you through its use. It puts it all together with a sample program.
Version: n/a Platform(s): n/a Updated: Wed Oct 3 2001
While it's common to hear that synchronized method calls can be 50 times as expensive as unsynchronized method calls, these numbers can actually be quite misleading. With each successive JVM version, overall performance has improved, and the cost of uncontended synchronization has been reduced, making the issue of uncontended synchronization overhead less significant. Contended synchronization, however, is quite expensive. Moreover, a high degree of contention is disastrous for scalability -- an application that had a high degree of contended synchronization will exhibit markedly worse performance as the load increases. This article explores several techniques for reducing contention, and hence improving scalability, in your programs.
In multithreaded code, it is often common to use a single, master thread that drives the actions the other threads take. This master thread may send messages, often by placing them on a queue, that are then processed by the other threads. But if the master thread throws an exception, the remaining threads may continue to run, awaiting more input to the queue, causing the program to freeze. This article discusses detecting, fixing, and avoiding this bug pattern.
Version: n/a Platform(s): n/a Updated: Fri Aug 31 2001
When special tags in fields are used to distinguish between types of objects, errors are possible in which a tag mislabels the associated data -- a bug pattern known as the Impostor Type. This article examines the symptoms and causes of this bug, defines ways to prevent this error from occurring, and discusses a tempting hybrid implementation that does not use impostor types but, in the end, turns out to have many of the same weaknesses. Article includes code snipets.
Many algorithms are expressed most concisely as tail-recursive methods. Compilers can automatically transform such methods into loops and thereby improve program performance, but this transformation is not required by the Java language specification, so not all JVMs will perform it. This means that tail-recursive methods in the Java language can result in unexpectedly large memory usage. This article demonstrates that dynamic compilation maintains the language's semantics while static compilation often doesn't. Learn why this matters and get a bit of code to help you determine whether your just-in-time (JIT) compiler can transform tail recursion on code while preserving semantics.
Version: n/a Platform(s): n/a Updated: Sat Jun 2 2001
You inevitably spend some part of your week crunching code that you didn't write, and for which you may not have the source. This beginner's guide to opening up and locking down Java code walks you through the essentials of disassembling, decompiling, and obfuscating Java code, using examples from popular tools such as Mocha, HoseMocha, jmangle, and JODE.
Version: n/a Platform(s): n/a Updated: Fri Jun 1 2001
