int size = myHashSet.size();
int item = new Random().nextInt(size); // In real life, the Random object should be rather more shared than this
int i = 0;
for(Object obj : myhashSet)
{
    if (i == item)
        return obj;
    i++;
}

Java 8最简单的方法是:

outbound.stream().skip(n % outbound.size()).findFirst().get()

其中n是一个随机整数。当然，它的性能不如使用for(elem: Col)

以霍斯的答案为起点的通用解决方案。

/**
 * @param set a Set in which to look for a random element
 * @param <T> generic type of the Set elements
 * @return a random element in the Set or null if the set is empty
 */
public <T> T randomElement(Set<T> set) {
    int size = set.size();
    int item = random.nextInt(size);
    int i = 0;
    for (T obj : set) {
        if (i == item) {
            return obj;
        }
        i++;
    }
    return null;
}

既然你说“其他语言的解决方案也欢迎”，下面是Python的版本:

>>> import random
>>> random.choice([1,2,3,4,5,6])
3
>>> random.choice([1,2,3,4,5,6])
4

Javascript解决方案;)

function choose (set) {
    return set[Math.floor(Math.random() * set.length)];
}

var set  = [1, 2, 3, 4], rand = choose (set);

或者:

Array.prototype.choose = function () {
    return this[Math.floor(Math.random() * this.length)];
};

[1, 2, 3, 4].choose();

读完这篇文章后，我能写的最好的是:

static Random random = new Random(System.currentTimeMillis());
public static <T> T randomChoice(T[] choices)
{
    int index = random.nextInt(choices.length);
    return choices[index];
}