main.groovy

def randomElement
// simulate user input, for instance
if (new Random().nextInt() % 2 == 0) {
    randomElement = new Element1()
} else {
    randomElement = new Element2()
}

printer(randomElement)

typeswitch.groovy

package com.jakecoffman.typeswitch

def printer(element) {
    switch (element.class) {
        case Element1:
            println "${element.name} ${element.element1Specific}"
            break
        case Element2:
            println "${element.name} ${element.element2Specific}"
            break
        default:
            throw new IllegalArgumentException("Unexpected class ${element.class.name}")
    }
}

class Element1 {
    String name
    String element1Specific

    Element1() {
        name = "Element1"
        element1Specific = "specific1"
    }
}

class Element2 {
    String name
    String element2Specific

    Element2() {
        name = "Element2"
        element2Specific = "specific2"
    }
}