Is this naive equals, hashcode OK?

Question

I have a class representing DB-Entries with a unique Id attribute. Is is OK to implement the equals() and hashcode() methods only based on this attribute

  @Override public int hashCode()
  { return id;
  }

  @Override public boolean equals(Object obj)
  {
    if (this == obj)                  return true;
    if (obj == null)                  return false;
    if (getClass() != obj.getClass()) return false;
    Task other = (Task) obj;
    if (id != other.id)
      return false;
    return true;
  }

Answer 1

In general, yes. If all the ids are small consecutive integers, you could get better performance from big collections by using a function which distributed the bits more widely throughout the available 32 bits. But this should work find otherwise.

Answer 2

I don't see anything wrong with this code. However, there are some questions you might wish to ponder:

• Can you ever have more than one object with the same id?
• Will the class ever be subclassed?