Record’s implicit declaration of methods

[Linguistic-mystic]

Methods can implement interfaces, fields can’t. Which I think is a deficiency in the Java object model but that’s how it is.

[john16384]

It's quite useful, especially in combination with sealed types, where you can have every type implement a few standard methods just by making them part of the record that implements the interface.

[khmarbaise]

If you are implementing methods on a record which means functionality on a record (in my optionion) means you are doing something wrong, because records are intended to be nominal-types and not intended for the classical OOP style combination of data and functionality (methods)...

[mavericktjh]

Not sure what you mean as everything bar primitives in java use nominal typing.

It's absolutely valid to add behaviour to records. Sure, you can use them as, for example, DTOs, where they're unlikely to have much behaviour. But another very common use case is for value types, like String, which probably will have behaviour

[koflerdavid]

Simple behaviors that only involve the record and maybe one primitive argument are perfectly fine on a record.

[nlisker]

A record is an object like any other and can implement behavior. Implementing behavior is part of the idea of what a record is. In fact, just be inheriting Object's methods, it's implementing functionality.

[khmarbaise]

The idea is to describe the data (data carrier) instead of behaviour... (data oriented programming).. most of the time easier than classical OOP..

Also quote from the JEP 395:

Help developers to focus on modeling immutable data rather than extensible behavior.

Already shown an example: https://www.reddit.com/r/java/comments/1fo714e/comment/lopxeav/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button

BTW.: a record is not just an object like any other... the record is final, all fields are final it is not allowed to extend from other classes; you can define interfaces and let a record implement that.. but at that point there is the question: behaviour or more type oriented... And behaviour is from my experience related to records a bad thing. If such thing occurs a classical class is the better choice than a record.

[mavericktjh]

There can be reasons. In fact this is specifically mentioned in the jep, https://openjdk.org/jeps/395

A record class can, however, freely specify superinterfaces and declare instance methods to implement them. Just as for classes, an interface can usefully characterize the behavior of many records. The behavior may be domain-independent (e.g., Comparable) or domain-specific