Task: Intersecting number wheels
C++: #include <initializer_list>
#include <iostream>
#include <map>
#include <vector>

struct Wheel {
private:
    std::vector<char> values;
    size_t index;

public:
    Wheel() : index(0) {
        
    }

    Wheel(std::initializer_list<char> data) : values(data), index(0) {
        
        if (values.size() < 1) {
            throw new std::runtime_error("Not enough elements");
        }
    }

    char front() {
        return values[index];
    }

    void popFront() {
        index = (index + 1) % values.size();
    }
};

struct NamedWheel {
private:
    std::map<char, Wheel> wheels;

public:
    void put(char c, Wheel w) {
        wheels[c] = w;
    }

    char front(char c) {
        char v = wheels[c].front();
        while ('A' <= v && v <= 'Z') {
            v = wheels[v].front();
        }
        return v;
    }

    void popFront(char c) {
        auto v = wheels[c].front();
        wheels[c].popFront();

        while ('A' <= v && v <= 'Z') {
            auto d = wheels[v].front();
            wheels[v].popFront();
            v = d;
        }
    }
};

void group1() {
    Wheel w({ '1', '2', '3' });
    for (size_t i = 0; i < 20; i++) {
        std::cout << ' ' << w.front();
        w.popFront();
    }
    std::cout << '\n';
}

void group2() {
    Wheel a({ '1', 'B', '2' });
    Wheel b({ '3', '4' });

    NamedWheel n;
    n.put('A', a);
    n.put('B', b);

    for (size_t i = 0; i < 20; i++) {
        std::cout << ' ' << n.front('A');
        n.popFront('A');
    }
    std::cout << '\n';
}

void group3() {
    Wheel a({ '1', 'D', 'D' });
    Wheel d({ '6', '7', '8' });

    NamedWheel n;
    n.put('A', a);
    n.put('D', d);

    for (size_t i = 0; i < 20; i++) {
        std::cout << ' ' << n.front('A');
        n.popFront('A');
    }
    std::cout << '\n';
}

void group4() {
    Wheel a({ '1', 'B', 'C' });
    Wheel b({ '3', '4' });
    Wheel c({ '5', 'B' });

    NamedWheel n;
    n.put('A', a);
    n.put('B', b);
    n.put('C', c);

    for (size_t i = 0; i < 20; i++) {
        std::cout << ' ' << n.front('A');
        n.popFront('A');
    }
    std::cout << '\n';
}

int main() {
    group1();
    group2();
    group3();
    group4();

    return 0;
}

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));
	}
}