一、去除List中重复的String
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());
二、List中对象去重
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。
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三、根据对象的属性去重
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)
);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)); 
