Use a common hash code algorithm, maybe forego including the collections ... which is not particularly problematic because they cause no exceptions in Java. Note that even great hashing algorithms ...

Java’s equals() and hashcode() are two methods that work together to verify if two objects have the same value. You can use them to make object comparisons easy and efficient in your Java programs.

As to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes. If two objects have the same hashcode then they are NOT necessarily equal.