Type

Gtype.groovy

class Gtype {

    def list;

    void write() {
        list.each {
            write(it)
        }
    }
    
    void write(Number n) {
        println "Number: ${n}"
    }

    void write(Integer n) {
        println "Integer: ${n}"
    }
}

new Gtype(list: [1, 1.1]).write()

Type.java

import java.util.List;

import static java.util.Arrays.asList;

public class Type {

    List<? extends Number> list;

    public Type(List<? extends Number> list) {
        this.list = list;
    }

    private void write() {
        for (Number i: list) {
            write(i);
        }
    }

    private void write(Number n) {
        System.out.println("Number: " + n);
    }

    private void write(Integer n) {
        System.out.println("Integer: " + n);
    }

    public static void main(String... args) {
        new Type(asList(1, 1.1)).write();
    }
}