Weighted randomization in Java

WeightedCollection.java

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

public class WeightedCollection<E> {
	
	private NavigableMap<Integer, E> map = new TreeMap<Integer, E>();
	private Random random;
	private int total = 0;
	
	public WeightedCollection() {
		this(new Random());
	}
	
	public WeightedCollection(Random random) {
		this.random = random;
	}
	
	public void add(int weight, E object) {
		if (weight <= 0) return;
		total += weight;
		map.put(total, object);
	}
	
	public E next() {
		int value = random.nextInt(total) + 1; // Can also use floating-point weights
		return map.ceilingEntry(value).getValue();
	}
	
}