public List<String> removeStringListDupli(List<String> stringList) { Set<String> set = new LinkedHashSet<>(); set.addAll(stringList); stringList.clear(); stringList.addAll(set); return stringList; } 或使用Java8的写法：
List<String> unique = list.stream().distinct().collect(Collectors.toList());
比如现在有一个 Person类:
public class Person { private Long id; private String name; public Person(Long id, String name) { this.id = id; this.name = name; } public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public String toString() { return "Person{" + "id=" + id + ", name='" + name + '\'' + '}'; } } 重写Person对象的equals()方法和hashCode()方法:
@Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Person person = (Person) o; if (!id.equals(person.id)) return false; return name.equals(person.name); } @Override public int hashCode() { int result = id.hashCode(); result = 31 * result + name.hashCode(); return result; } 下面对象去重的代码：
Person p1 = new Person(1l, "jack"); Person p2 = new Person(3l, "jack chou"); Person p3 = new Person(2l, "tom"); Person p4 = new Person(4l, "hanson"); Person p5 = new Person(5l, "胶布虫"); List<Person> persons = Arrays.asList(p1, p2, p3, p4, p5, p5, p1, p2, p2); List<Person> personList = new ArrayList<>(); // 去重 persons.stream().forEach( p -> { if (!personList.contains(p)) { personList.add(p); } } ); System.out.println(personList); List 的contains()方法底层实现使用对象的equals方法去比较的，其实重写equals()就好，但重写了equals最好将hashCode也重写了。
可以参见:http://stackoverflow.com/questions/30745048/how-to-remove-duplicate-objects-from-java-arraylist
https://www.jb51.net/article/243751.htm
下面要根据Person对象的id去重，那该怎么做呢？
写一个方法吧:
public static List<Person> removeDupliById(List<Person> persons) { Set<Person> personSet = new TreeSet<>((o1, o2) -> o1.getId().compareTo(o2.getId())); personSet.addAll(persons); return new ArrayList<>(personSet); } 通过Comparator比较器，比较对象属性，相同就返回0，达到过滤的目的。
再来看比较炫酷的Java8写法:
import static java.util.Comparator.comparingLong; import static java.util.stream.Collectors.collectingAndThen; import static java.util.stream.Collectors.toCollection; // 根据id去重 List<Person> unique = persons.stream().collect( collectingAndThen( toCollection(() -> new TreeSet<>(comparingLong(Person::getId))), ArrayList::new) );
这段炫酷的代码是google的，还不明白是怎么个原理，等我好好研究一下，再专门写篇文章好好阐述一下。
还有一种写法:
public static <T> Predicate<T> distinctByKey(Function<? super T, Object> keyExtractor) { Map<Object, Boolean> map = new ConcurrentHashMap<>(); return t -> map.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null; } // remove duplicate persons.stream().filter(distinctByKey(p -> p.getId())).forEach(p -> System.out.println(p)); java8 确实简化了很多冗长的操作，精简了代码，小伙，研究java8去吧！