Correctness: Overriding equals, but not hashCode

[michaeldiamant]

Subject of the issue

While working on #340 (comment), I observed numerous instances where equals is overwritten, but not hashCode.

The status quo breaks hashCode's contract as discussed in https://stackoverflow.com/questions/2265503/why-do-i-need-to-override-the-equals-and-hashcode-methods-in-java.

Your environment

N/A

Steps to reproduce

N/A

Expected behaviour

There's at least 2 solutions:

• Immediately - Consistently override hashCode and equals. Prefer using an IDE-generated implementation.
• Longer term - Upgrade to >= JDK 16 and replace class definitions with records (https://docs.oracle.com/en/java/javase/16/language/records.html). Among other benefits, records obviate the need to manage equals and hashCode implementations.

Actual behaviour

N/A

Acceptance Criteria

1. Updating hand written code to implement both functions.
2. Update code generator to generate hashCode along with equals, then regenerate the code.

[winder]

For the good first issue, implementing the first part of this would be helpful:

1. Updating hand written code to implement both functions.