GCViewerGCViewer (download) is a free open source tool to visualize data produced by the Java VM options -verbose:gc and -Xloggc:<file>. It also calculates garbage collection related performance metrics (throughput, accumulated pauses, longest pause, etc.). This can be very useful when tuning the garbage collection of a particular application by changing generation sizes or setting the initial heap size.
Javaパフォーマンス管理 － ＠IT
http://www.nextindex.net/java/perform/garbage.html
Java 仮想マシンの空きメモリ容量を取得する / Java(SE) API 逆引き辞典
