Task: Intersecting number wheels
Go: package main

import (
    "fmt"
    "sort"
    "strconv"
)

type wheel struct {
    next   int
    values []string
}

type wheelMap = map[string]wheel

func generate(wheels wheelMap, start string, maxCount int) {
    count := 0
    w := wheels[start]
    for {
        s := w.values[w.next]
        v, err := strconv.Atoi(s)
        w.next = (w.next + 1) % len(w.values)
        wheels[start] = w
        if err == nil {
            fmt.Printf("%d ", v)
            count++
            if count == maxCount {
                fmt.Println("...\n")
                return
            }
        } else {
            for {
                w2 := wheels[s]
                ss := s
                s = w2.values[w2.next]
                w2.next = (w2.next + 1) % len(w2.values)
                wheels[ss] = w2
                v, err = strconv.Atoi(s)
                if err == nil {
                    fmt.Printf("%d ", v)
                    count++
                    if count == maxCount {
                        fmt.Println("...\n")
                        return
                    }
                    break
                }
            }
        }
    }
}

func printWheels(wheels wheelMap) {
    var names []string
    for name := range wheels {
        names = append(names, name)
    }
    sort.Strings(names)
    fmt.Println("Intersecting Number Wheel group:")
    for _, name := range names {
        fmt.Printf("  %s: %v\n", name, wheels[name].values)
    }
    fmt.Print("  Generates:\n    ")
}

func main() {
    wheelMaps := []wheelMap{
        {
            "A": {0, []string{"1", "2", "3"}},
        },
        {
            "A": {0, []string{"1", "B", "2"}},
            "B": {0, []string{"3", "4"}},
        },
        {
            "A": {0, []string{"1", "D", "D"}},
            "D": {0, []string{"6", "7", "8"}},
        },
        {
            "A": {0, []string{"1", "B", "C"}},
            "B": {0, []string{"3", "4"}},
            "C": {0, []string{"5", "B"}},
        },
    }
    for _, wheels := range wheelMaps {
        printWheels(wheels)
        generate(wheels, "A", 20)
    }
}

Java: package intersectingNumberWheels;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.IntStream;

public class WheelController {
	private static final String IS_NUMBER = "[0-9]";
	private static final int TWENTY = 20;
	private static Map<String, WheelModel> wheelMap;

	public static void advance(String wheel) {
		WheelModel w = wheelMap.get(wheel);
		if (w.list.get(w.position).matches(IS_NUMBER)) {
			w.printThePosition();
			w.advanceThePosition();
		} else {
			String wheelName = w.list.get(w.position);
			advance(wheelName);
			w.advanceThePosition();
		}
	}

	public static void run() {
		System.out.println(wheelMap);
		IntStream.rangeClosed(1, TWENTY).forEach(i -> advance("A"));
		System.out.println();
		wheelMap.clear();
	}

	public static void main(String[] args) {
		wheelMap = new HashMap<>();
		wheelMap.put("A", new WheelModel("A", "1", "2", "3"));
		run();
		wheelMap.put("A", new WheelModel("A", "1", "B", "2"));
		wheelMap.put("B", new WheelModel("B", "3", "4"));
		run();
		wheelMap.put("A", new WheelModel("A", "1", "D", "D"));
		wheelMap.put("D", new WheelModel("D", "6", "7", "8"));
		run();
		wheelMap.put("A", new WheelModel("A", "1", "B", "C"));
		wheelMap.put("B", new WheelModel("B", "3", "4"));
		wheelMap.put("C", new WheelModel("C", "5", "B"));
		run();
	}

}

class WheelModel {
	String name;
	List<String> list;
	int position;
	int endPosition;
	private static final int INITIAL = 0;

	public WheelModel(String name, String... values) {
		super();

		this.name = name.toUpperCase();
		this.list = new ArrayList<>();
		for (String value : values) {
			list.add(value);
		}
		this.position = INITIAL;
		this.endPosition = this.list.size() - 1;
	}

	@Override
	public String toString() {
		return list.toString();
	}

	public void advanceThePosition() {
		if (this.position == this.endPosition) {
			this.position = INITIAL;
		} else {
			this.position++;
		}
	}

	public void printThePosition() {
		System.out.print(" " + this.list.get(position));
	}
}