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Here, Timer.schedule() expects a TimerTask as its argument, so Nashorn creates an instance of a TimerTask subclass and uses the passed function to implement its only abstract method, run(). In this usage though, you can't use non-default constructors; the type must be either an interface, or must have a protected or public no-arg constructor.

Java.extend function

Java.extend function returns a type object for a subclass of the specified Java class (or implementation of the specified interface) that acts as a script-to-Java adapter for it. Note that you can also implement interfaces and subclass abstract classes using new operator on a type object for an interface or abstract class. However, to extend a non-abstract class, you will have to use this method. Example:

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var anArray = [1, "13", false]

// Java.to used to convert script array to a Java int array
var javaIntArray = Java.to(anArray, "int[]")

print(javaIntArray[0])  // prints 1
print(javaIntArray[1])  // prints 13, as string "13" was converted to number 13 
                        // as per ECMAScript ToNumber conversion
print(javaIntArray[2])  // prints 0, as boolean false was converted to number 0
                        // as per ECMAScript ToNumber conversion

Java.super function

When given an object created using Java.extend() or equivalent mechanism (that is, any JavaScript-to-Java adapter), Java.super returns an object that can be used to invoke superclass methods on that object. E.g.:

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