/sys$common/syshlp/helplib.hlb JAVA, Qualifiers, /MAXHEAP  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /MAXHEAP=x
       -mx x

    Sets the maximum size of the memory allocation pool (the garbage
    collected heap) to x. The default is 6 megabytes of memory. The
    value of x must be greater than or equal to 1000 bytes.

    By default, x is measured in bytes. You can specify x in either
    kilobytes or megabytes by appending the letter k for kilobytes or
    the letter m for megabytes.