Java Performance

One of the most widespread misconceptions about Java is that it is slow. Today, with the existence of highly optimized JITs (Just in Time Compilers), this is not longer true on most platforms. Most Java applications run with as little as 20-40% overhead compared to traditional optimized C++ code. And in multithreaded applications, as e.g. applications relying heavily on I/O, no measurable performance difference exists between Java and C++, due to Java's excellent built in support for multithreading.

With the advent of more sophisticated dynamic compiling in the upcoming HotSpot runtime, Java programs may actually be able to run quicker than C++ code, due to the fact that dynamic recompiling (which is what a JIT is really about) can morph the program to match the actual code dispatches and the underlying runtime in a way that isn't possible with static compilers, which traditional languages like C++ rely on. (One of the advantages whith dynamic compiling is that the compiler can choose to dynamically inline code, due to knowledge of frequent code dispatch paths - a feature that isn't possible in static compiling of object oriented code to the same extent, as the compiler then doesn't know if a method may actually be inherited in another part of the application.)

Part of the performance of Java is also its robustness and built in security, making it much easier to write safe and stable applications than would be possible in C++. Java's dynamic linking and bytecode-format, which retains method names and signatures in the compiled code, makes it easy to maintain the code, and to distribute it on networks - a fact that is well known to the internet community today. With the upcoming Embedded Javaplatform,  Java will also enter consumer electronics, giving the "Write once - run anywhere" a new dimension.

Of course there are some benchmarks for comparing different Java platforms, such as CaffeineMark and ByteMark, and some nice links on Java Optimization. A nice tool for graphical profiling is HyperProf.