Generation* GenerationSpec::init(ReservedSpace rs, int level,
                                 GenRemSet* remset) {

  {- -------------------------------------------
  (1) 指定された名前に応じて, 以下の switch-case で
      適切な Generation クラスのコンストラクタを呼び出し, 
      生成された Generation オブジェクトをリターンする.

      (ただし, ConcurrentMarkSweep と ASConcurrentMarkSweep の場合は, コンストラクタ呼び出し後に 
       ConcurrentMarkSweepGeneration::initialize_performance_counters() を呼び出してからリターン)
      ---------------------------------------- -}

      switch (name()) {
        case Generation::DefNew:
          return new DefNewGeneration(rs, init_size(), level);

        case Generation::MarkSweepCompact:
          return new TenuredGeneration(rs, init_size(), level, remset);

    #ifndef SERIALGC
        case Generation::ParNew:
          return new ParNewGeneration(rs, init_size(), level);

        case Generation::ASParNew:
          return new ASParNewGeneration(rs,
                                        init_size(),
                                        init_size() /* min size */,
                                        level);

        case Generation::ConcurrentMarkSweep: {
          assert(UseConcMarkSweepGC, "UseConcMarkSweepGC should be set");
          CardTableRS* ctrs = remset->as_CardTableRS();
          if (ctrs == NULL) {
            vm_exit_during_initialization("Rem set incompatibility.");
          }
          // Otherwise
          // The constructor creates the CMSCollector if needed,
          // else registers with an existing CMSCollector

          ConcurrentMarkSweepGeneration* g = NULL;
          g = new ConcurrentMarkSweepGeneration(rs,
                     init_size(), level, ctrs, UseCMSAdaptiveFreeLists,
                     (FreeBlockDictionary::DictionaryChoice)CMSDictionaryChoice);

          g->initialize_performance_counters();

          return g;
        }

        case Generation::ASConcurrentMarkSweep: {
          assert(UseConcMarkSweepGC, "UseConcMarkSweepGC should be set");
          CardTableRS* ctrs = remset->as_CardTableRS();
          if (ctrs == NULL) {
            vm_exit_during_initialization("Rem set incompatibility.");
          }
          // Otherwise
          // The constructor creates the CMSCollector if needed,
          // else registers with an existing CMSCollector

          ASConcurrentMarkSweepGeneration* g = NULL;
          g = new ASConcurrentMarkSweepGeneration(rs,
                     init_size(), level, ctrs, UseCMSAdaptiveFreeLists,
                     (FreeBlockDictionary::DictionaryChoice)CMSDictionaryChoice);

          g->initialize_performance_counters();

          return g;
        }
    #endif // SERIALGC

        default:
          guarantee(false, "unrecognized GenerationName");
          return NULL;
      }
    }