Java-比较两个具有共同值的字符串列表，并返回多少个相同项

Question

我想比较两个列表，并检查它们是否有共同点。

例子

List<String> list1 = new ArrayList();

list1.add("id1");

list1.add("id2");

list1.add("id3");

list1.add("id10");

List<String> list2 = new ArrayList();

list2.add("id10");

list2.add("id20");

list2.add("id3");

list2.add("id30");

list2.add("id31");

并返回在最短和最佳的过程中有多少个项目具有相同的值。

Answer 1

一种方法是，将两个列表中的元素放入Set，检查是否set.size()与list1.size()+list2.size()diff将是重复元素的计数。

Answer 2

试试这个 ：ArrayList intersection = new ArrayList<>(list1);intersection.retainAll(list2);相交处将包含共同要素

Answer 3

使用以下代码：&nbsp; &nbsp; Set<String> set =&nbsp; new HashSet<>(list1);&nbsp; &nbsp; set.addAll(list2);&nbsp; &nbsp; System.out.println(((list1.size() + list2.size()) - set.size()));

Answer 4

我不知道这是否是最有效的方法，但我会做这样的事情：public static int getCommonValues() {&nbsp; &nbsp; int values = 0;&nbsp; &nbsp; if(list1 != null && list2 != null) {&nbsp; &nbsp; &nbsp; &nbsp; Iterator it = list1.iterator();&nbsp; &nbsp; &nbsp; &nbsp; while(it.hasNext()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; String value = it.next();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Iterator it2 = list2.iterator();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; while(it2.hasNext()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; String value2 = it2.next();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if(value2 == value) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; values = values + 1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; break;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }&nbsp; &nbsp; return values;}