question: synchronized int lookup ( final Object tx , final boolean insert ) { if ( tx == null ) { throw new IllegalArgumentException ( "transaction object is null" ) ; } Integer index = ( Integer ) mapping . get ( tx ) ; if ( index == null ) { if ( insert ) { final int capacity = capacity ( ) ; final int nvertices = mapping . size ( ) ; if ( nvertices == capacity ) { throw new MultiprogrammingCapacityExceededException ( "capacity=" + capacity + ", nvertices=" + nvertices ) ; } index = ( Integer ) indices . remove ( 0 ) ; mapping . put ( tx , index ) ; final int ndx = index . intValue ( ) ; if ( transactions [ ndx ] != null ) { throw new AssertionError ( ) ; } transactions [ ndx ] = tx ; } else { return - 1 ; } } return index . intValue ( ) ; }
target:  Lookup index assigned to transaction object.