code: public static AtomTypeMapper getInstance(String mappingFile) {
          if (!mappers.containsKey(mappingFile)) {
              mappers.put(mappingFile, new AtomTypeMapper(mappingFile));
          }
          return mappers.get(mappingFile);
      }
docs: Instantiates an atom type to atom type mapping, based on the given mapping file.
  For example, the mapping file <code>org.openscience.cdk.config.data.cdk-sybyl-mappings.owl</code>
  which defines how CDK atom types are mapped to Sybyl atom types.
  
  @param  mappingFile File name of the OWL file defining the atom type to atom type mappings.
  @return             An instance of AtomTypeMapper for the given mapping file.