Java Nashorn - How to define a JavaScript function in Java which accepts an anonymous function as an argument?

Question

Basically what I'm trying to do is to create a new function, which can be used in JavaScript, but it would require a string and an anonymous function to be passed as arguments. The anonymous function would also have to supply an argument of it's own.

In the JavaScript I would like to have:

addEventHandler( "eventName", function ( event ) {
    // do stuff
});

and the way I'd like Java to interpret that is like so:

addEventHandler ( "eventName", event -> {
    // do stuff
});

Is this possible? At all? Thank you in advance!

Answer 1

If you have a Java method that accepts a functional interface as an argument, you can pass an anonymous function in javascript.

For instance:

public static void main(String[] args) throws Throwable {
    ScriptEngine se = new ScriptEngineManager().getEngineByExtension("js");

    se.put("myObject", new MyClass());

    se.eval("myObject.someMethod('hello', function(e){ print(e); })");
}

public static class MyClass { // Class needs to be public
    public void someMethod(String s, Consumer<String> cons) {
        System.out.println(s);
        cons.accept("SomeString");
    }       
}

Prints:

hello
SomeString