Daniel Høyer Jacobsen

Follow The Guidelines Of The Equals-Method
The equals-method need to obey the following four rules to remain functional.

Reflexive: x.equals(x) = true

Symmertric: x.equals(y) = y.equals(x)

Transitive: x.equals(y) = y.equals(z) = true -> z.equals(x) = true

Consistent: x.equals(y) remains the same as long as x and y does not change.

How to write a good equals method:

(Regardless of most IDEs autogenerating them)

First use == to check if the object is equivilent to “this”.
Use instanceof to check if the object is the correct class instance. Otherwise return false.
Cast the object to the same instance as “this”
Check with == if all relevant fields of the class match each other.

1. Use Static Factory Methods Instead Of Constructors
Instead of overloading multiple constructors with different arguments, just make static methods. This way you can explain the intent of each constructed objects, regardless of it being the same class.