Interview example [closed]

Question

Recently I participated in an interview for a Russian company in Moskow and could not answer some of the simple questions. One of them I would like to ask here.

List all problems which you can see in the following code:

public abstract class Digest {
  private Map<byte[], byte[]> cache = new HashMap<byte[], byte[]>();

  public byte[] digest(byte[] input) {
      byte[] result = cache.get(input);
      if (result == null) {
          synchronized (cache) {
              result = cache.get(input);
              if (result == null) {
                  result = doDigest(input);
                  cache.put(input, result);
              }
          }
      }
      return result;
  }

  protected abstract byte[] doDigest(byte[] input);
  }

Answer 1

Try this link

It seems it may be a standard interview question as interviewees have previously posted it on Stack Overflow. Or maybe interviewers are getting lazy and have started lifting their questions directly from Stack Overflow in the first place?