android/guava/src/com/google/common/collect/MapMaker.java
public <K, V> ConcurrentMap<K, V> makeMap() {
    if (!useCustomMap) {
      return new ConcurrentHashMap<>(getInitialCapacity(), 0.75f, getConcurrencyLevel());
    }
    return MapMakerInternalMap.create(this);
  }
public <K, V> ConcurrentMap<K, V> makeMap() {
    if (!useCustomMap) {
      return new ConcurrentHashMap<>(getInitialCapacity(), 0.75f, getConcurrencyLevel());
    }
    return MapMakerInternalMap.create(this);
  }
Builds a thread-safe map. This method does not alter the state of this {@code MapMaker}
instance, so it can be invoked again to create multiple independent maps.

<p>The bulk operations {@code putAll}, {@code equals}, and {@code clear} are not guaranteed to
be performed atomically on the returned map. Additionally, {@code size} and {@code
containsValue} are implemented as bulk read operations, and thus may fail to observe concurrent
writes.

@return a serializable concurrent map having the requested features