Method intern

output/java_guava/1.4.19/Interners.java:48–52

(E sample)

    final ConcurrentMap<E, E> map = new MapMaker().makeMap();
    return new Interner<E>() {
      @Override
      public E intern(E sample) {
        E canonical = map.putIfAbsent(checkNotNull(sample), sample);
        return (canonical == null) ? sample : canonical;
      }
    };
  }