Enums can have abstract methods.
public enum MODE {
  PACK_8 {
    public in getOffsetIncrementMultiplier() { return 4; };
  },
  PACK_32 {
    public in getOffsetIncrementMultiplier() { return 1; };
  };
  public abstract int getOffsetIncrementMultiplier();
}

offset += 1 + mode.getOffsetIncrementMultiplier() * page[offset];