A Vein

public class Vein {
    private int sum;
    private List<Vein> subveins;
    private String name;
    private int weight;

    public Vein(String name, int weight) {
        this.name = Objects.requireNonNull(name);
        this.weight = Math.max(weight, 1);
        this.sum = 0;
        this.subveins = new ArrayList<>();
    }

    public void addSubVein(Vein other) {
        subveins.add(Objects.requireNonNull(other))
        sum+= other.getWeight();
    }

    pubic Vein selectVein() {
        if (subveins.isEmpty())
            return this;
        int random = Math.floor(Math.random()*sum);
        int curSum = 0;
        int i = 0;
        for (; i < subveins.size() && curSum < random; ++i) {
            curSum+=subveins.get(i).getWeight();
        }
        return subveins.get(Math.min(i, subveins.size()-1));
    }

    pubic int getWeight() {
        return weight;
    }

    public String getName() {
        return name;
    }
}