Tools for Optimizing Java

[ index ] [ benchmarks | compilers | maintainability | resources | rules | size | speed ]

Profiling:

To profile a (single-threaded) application, use java -prof. To profile an applet, use java -prof sun.applet.AppletViewer myfile.html (tip from David Moore). The profile file can then be analyzed using a tool such as Profile Viewer or HyperProf. You can also use the profiling tools built into an IDE such as VisionSoft

Note that commercial profilers such as Optimize It! can profile both time and memory.

Disassembly:

Use javap -c to see the bytecode that your Java is compiled into:

	javac -O test.java
	javap -c test | more

To understand the bytecode, read the Java VM spec.

Timing:

Write a timing harness to wrap around code fragments so that you can benchmark them. You can either adapt the old thread-based HotJava Performance Tests, or just use a simple loop. Note that system.currentTimeMillis() returns the time of day, not the process time, so all benchmarking should be done on an idle machine. Call system.gc() before every timing run to minimize inconsistent results due to garbage collection in the middle of a run. On systems with sub-millisecond clocks you can use native methods to access them (e.g., gettimeofday() or getrusage() on Unix systems).

Memory use:

You can write a memory-use harness in just the same way you'd write a timing harness, replacing calls to system.currentTimeMillis() with calls to

	long freemem ()	{
	  System.gc();
	  return Runtime.getRuntime().freeMemory();
	}
    

(tip from Glen McCluskey).