Method putIfAbsent

guava/src/com/google/common/cache/LocalCache.java:4216–4222

(K key, V value)

  }

  @Override
  public @Nullable V putIfAbsent(K key, V value) {
    checkNotNull(key);
    checkNotNull(value);
    int hash = hash(key);
    return segmentFor(hash).put(key, hash, value, true);
  }

  @Override
  public @Nullable V compute(