question: checkout object from pool concode_field_sep HashSet<T> inUse concode_elem_sep HashSet<T> available concode_field_sep void checkIn concode_elem_sep T create concode_elem_sep String toString
target: T function ( ) { if ( available . size ( ) <= 0 ) { available . add ( create ( ) ) ; } T loc0 = available . iterator ( ) . next ( ) ; available . remove ( loc0 ) ; inUse . add ( loc0 ) ; return loc0 ; }