Java compare two sub objects

Question

I have a class - it has a field "id", which is an int. Let's call this class "Author".

I have another class, it has a field "author", which is an "Author". Let's call this class "Book".

If I have two book objects, what is the best way to note the difference (if any) in the id of the author?

The "id" field could be null, and the "author" field could also be null. Is there some pre-written code that can handle all the plausible permutations for null checks?

question from:https://stackoverflow.com/questions/66047557/java-compare-two-sub-objects

Answer 1

You must correctly implement equals method for your classes, looking also at inner objects, using something like this

@Override 
public boolean equals(Object o) {
  if (o == this) return true;
  if (!(o instanceof Book)) return false;
  Book other = (Book) o;
  if (!other.canEqual((Object)this)) return false;
  if (!super.equals(o)) return false;
  if (!this.other.author.equals(this.author)) return false;
  return true;
}

If don't want particular behaviour you can use Lombok with its @EqualsAndHashCode annotation