获取list集合中重复的元素
方法1
List<String> words = Arrays.asList("a", "b", "c", "d", "a", "d");
List<String> results = HashMultiset.create(words).entrySet().stream()
.filter(w -> w.getCount() > 1)
.map(Multiset.Entry::getElement)
.collect(Collectors.toList());
System.out.println(results);
方法2
可以修改返回值 返回去重的集合
public static <E> List<E> getListDuplicateElements(List<E> list){
List<E> words = list;
Set<E> repeated = new HashSet<>();
List<E> results = new ArrayList<>();
for (E word : words) {
if (!repeated.add(word)) {
results.add(word);
}
}
return results;
}
方法3
导入guava依赖
<!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>31.0-jre</version>
</dependency>
List<String> words = Arrays.asList("a", "b", "c", "d", "a", "d");
List<String> results = new ArrayList<>();
for (Multiset.Entry<String> entry : HashMultiset.create(words).entrySet()) {
if (entry.getCount() > 1) {
results.add(entry.getElement());
}
}
System.out.println(results);
Lambda 来使用guava
List<String> words = Arrays.asList("a", "b", "c", "d", "a", "d");
List<String> results = HashMultiset.create(words).entrySet().stream()
.filter(w -> w.getCount() > 1)
.map(Multiset.Entry::getElement)
.collect(Collectors.toList());
System.out.println(results);
方法4
public List getRepeatList(List list) {
List list2 = new ArrayList();
for (int i = 0; i < list.size(); i++) {
for (int j = i + 1; j < list.size(); j++) {
if (list.get(i) !="" && list.get(i).equals(list.get(j))) {
list2.add(list.get(i));
break;
}
}
}
return list2;
}
/**
* 获取list 集合重复元素
*
* @param list
* @param <E>
* @return
*/
public static <E> List<E> getDuplicateElements(List<E> list) {
return list.stream() .filter( i -> i!="") // list 对应的 Stream 并过滤""
.collect(Collectors.toMap(e -> e, e -> 1, Integer::sum)) // 获得元素出现频率的 Map，键为元素，值为元素出现的次数
.entrySet()
.stream() // 所有 entry 对应的 Stream
.filter(e -> e.getValue() > 1) // 过滤出元素出现次数大于 1 (重复元素）的 entry
.map(Map.Entry::getKey) // 获得 entry 的键（重复元素）对应的 Stream
.collect(Collectors.toList()); // 转化为 List
}
