code: public void put(K key, V value)
      {
          this.lock.writeLock().lock();
  
          try {
              this.map.put(key, new SoftReference<>(value));
          } finally {
              this.lock.writeLock().unlock();
          }
      }
docs: Associate passed key to passed value.
  
  @param key the entry key
  @param value the entry value