Extending Java classes from JavaScript code

[madoar]

I'm interested to learn how to extend Java classes/interfaces with graal.js.
I know of the "nashorn way" to extend Java classes/interfaces, which is using either the new operator or to use Java.extend, but I'm not sure how this can be achieved in graal.js without the nashorn compatibility mode?

[wirthi]

Hi madoar,

thanks for your question. As of RC5 (published early August), Java.extend will be available by default, outside Nashorn compatibility mode.

The syntax extension around new Interface|AbstractClass(fn|obj) is still only available in Nashorn compatibility mode. Users writing new code should be able to use Java.extend for all cases; we will continue to monitor this.

Best,
Christian

[madoar]

Thank you for the information!

This leads me to another question.
With Graal.js supporting the "new" class syntax of ECMAScript 6, I'm asking myself if it's planned to support this syntax for the extension of Java classes.

In my eyes, it would be ideal if it's possible to extend a Java class AbstractClass by using:

class ConcreteClass extends AbstractClass {
   ...
}

or

class ConcreteClass extends Java.type("AbstractClass") {
   ...
}

[woess]

@madoar I like the idea of using the class syntax, but I have some reservations about mixing JS and Java class semantics. It raises some questions about how class evaluation has to be changed to support this, and you'll only really know at runtime if you're extending a Java class.

We'll consider it in the future, but for the time being we'll only support the "Nashorn way" (that comes from a time when JS didn't have classes yet).