Create a data collection to randomly pick it up.

RandomCollection.java

import java.util.NavigableMap;
import java.util.Random;
import java.util.TreeMap;

public class RandomCollection<E> {

    private final NavigableMap<Double, E> map = new TreeMap<>();
    private final Random random;
    private double total = 0;

    public RandomCollection() {
        this(new Random());
    }

    public RandomCollection(Random random) {
        this.random = random;
    }

    public void add(double chance, E result) {
        if (chance <= 0) return;
        total += chance;

        map.put(total, result);
    }

    public E next() {
        double value = random.nextDouble() * total;
        return map.higherEntry(value).getValue();
    }

}