Records

Records are a new preview feature in Java 14 providing a nice concise syntax to declare classes that are supposed to be dumb data holders.

You can read here (Records (preview language feature) section) for more details. Also, in part V I’m provided you most part of the implementation with explanation.

Here’s a simple record example:

public record Color(String name, int code) {}

Given this simple one-liner, Java compiler generates appropriate implementations for accessor methods, toString, equals, and hashcode.

In order to implement toString, equals, or hashcode, Java is using invokedynamic

The alternative solution is to find all record fields and generate the equals logic based on those fields at compile-time. The more we have fields, the lengthier the bytecode.

On the contrary, Java calls a bootstrap method to link the appropriate implementation at runtime. Therefore, the bytecode length would remain constant regardless of the number of fields.

https://www.baeldung.com/java-invoke-dynamic

So, for records, compilers emits bytecode that encoded all static parameters type, and actual parameters value for toString, equals, and hashcode.

Note: The bootstrap method in this case is not public. So, this may change without notice.

Currently, there is single bootstrap method for all methods. This is ObjectMethods#bootstrap (it revives methodName as one of it’s parameters, that it used to differentiate what method should be implemented).

Senior Software Engineer at Pursway