public class Main {

    public static void main(String[] args) {

        Integer i = new Integer(42);
        Double d = new Double(3.14156);
        String s = new String ("All your base are belong to us!");

        Object o = null;
        handle(o);
        o = i;
        handle(o);
        o = d;
        handle(o);
        o = s;
        handle(o);
    }

    private static void handle(String arg) {
        System.out.println("It's a string!");
    }


    private static void handle(Number arg) {
        System.out.println("It's a number!");
    }


    private static void handle(Double arg) {
        System.out.println("It's a double!");
    }

    private static void handle(Object arg) {
        System.out.println("no idea what it is...");
    }

}