The Java Virtual Machine (JVM) heap size is one of those things I've read about but never thought I'd need to mess with. My dilettante Java programs have always run just fine with the defaults... until that is I tried sending 160,000 data points to a JFreeChart scatter graph running in ZK on Tomcat.

A Java Virtual Machine on 32-bit operating systems typically has a maximum heap size of 64Mb. The JVM heap space is where all Java objects are stored, as well as memory used by the garbage collector. Sun recommends increasing this value for server applications, see Tuning Garbage Collection with the 5.0 Java[tm] Virtual Machine: