如何计算两个以上HashSet之间的交集？

Question

考虑下面的代码以及HashSet4s在其他地方填充的事实.

我的目标是包含所有4个HashSets中常见的所有元素.

我的问题是,首先,我做得对吗？其次,如果我做得对,有没有更好的方法呢？如果没有,那么我对此问题有什么解决方案？

static Set<String> one=new HashSet<>();
static Set<String> two=new HashSet<>();
static Set<String> three=new HashSet<>();
static Set<String> four=new HashSet<>();

private static void createIntersectionQrels() {
    ArrayList<String> temp = new ArrayList<>();
    Set<String> interQrels = new HashSet<>();

    temp.addAll(one);
    one.retainAll(two);
    interQrels.addAll(one);
    one.addAll(temp);
    one.retainAll(three);
    interQrels.addAll(one);
    one.addAll(temp);
    one.retainAll(four);
    interQrels.addAll(one);
    one.addAll(temp);

    interQrels.retainAll(two);
    interQrels.retainAll(three);
    interQrels.retainAll(four);
}

Answer 1

我想你可以简单地调用retainAll()第一组,使用第二,第三和第四组作为参数:

private static Set<String> getIntersectionSet() {
    // create a deep copy of one (in case you don't wish to modify it)
    Set<String> interQrels = new HashSet<>(one);

    interQrels.retainAll(two);     // intersection with two (and one)
    interQrels.retainAll(three);   // intersection with three (and two, one)
    interQrels.retainAll(four);    // intersection four (and three, two, one)

    return interQrels;
}