There are situations where writing lamda function is hard and it would be really nice to get code completion help. For example this method:

https://dukescript.com/javadoc/libs/net/java/html/lib/jquery/JQuery.html#addClass-net.java.html.lib.Function.A2-

isn't particularly easy to write:

JQuery q;
q.addClass(|

in a code like

import net.java.html.lib.Function;
import static net.java.html.lib.jquery.Exports.$;

public class Test {
    public static void main(String... args) {
        $("x").addClass(new Function.A2<Number, String, String>() {
            @Override
            public String call(Number p1, String p2) {
                return null;
            }
       });
    }
}

and generate the lamda automatically

import static net.java.html.lib.jquery.Exports.$;

public class Test {
    public static void main(String... args) {
        $("x").addClass((Number p1, String p2) -> null);
    }
}