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Necessity of volatile array write while in synchronized block
// Cache of byte[] data by row and column.
  private volatile byte[][][] cache;

  public byte[] getData(int row, int col)
  {
    return cache[row][col];
  }

  public void updateData(int row, int col, byte[] data)
  {
    synchronized(cache)
    {
      if (!Arrays.equals(data,cache[row][col]))
      {
        cache[row][col] = data;

        // Volatile write.
        // The below line is intentional to ensure a volatile write is
        // made to the array, since access via getData is unsynchronized.
        this.cache = this.cache;

        // Notification code removed
        // (mentioning it since it is the reason for synchronizing).
      }
    }
  }

private final    byte[][][] cacheF = new ...;  // dimensions fixed?
  private volatile byte[][][] cacheV = cacheF;

  public byte[] getData(int row, int col)
  {
    return cacheV[row][col];
  }

  public void updateData(int row, int col, byte[] data)
  {
    synchronized(cacheF)
    {
      if (!Arrays.equals(data,cacheF[row][col]))
      {
        cacheF[row][col] = data;

        cacheV = cacheF;
      }
    }
  }

private volatile byte[][]cache = ...;
cache[row][col] = data;

private final byte[][]cache = ...;
cache[row][col] = data;