this is related2 java can i call garbage collector explicitly if so how?

Answer 1

You can call System.gc(), but that is only a *request* to perform garbage collection.

You should also take a look at the documents here http://java.sun.com/javase/technologies/hotspot.jsp to learn about how to configure the size of the different parts of the heap and configure different GC implementations depending on your application and intended environment, e.g. multi-cpu server, single cp client/desktop app, etc.