Sets the value used by the garbage collector to determine the number of garbage collections after which a soft reference is cleared if its referent has not been marked.
The default value is 32.
A soft reference (where its referent is not marked) is cleared after a number of garbage collection cycles calculated as:
<value> * (proportion of free heap space)
For example, if
-Xsoftrefthreshold is set to 32, and the heap is 25% free, soft references are cleared after 8 garbage collection cycles.