Java-List去掉重复对象

我会带着你远行 2021-10-12 23:00 521阅读 0赞

## 一、去除List中重复的String ##

Set<String> set = new LinkedHashSet<>();
       set.addAll(list);
       list.clear();
       list.addAll(set);

或使用Java8的写法：

List<String> list = list.stream().distinct().collect(Collectors.toList());

##  二、List中对象去重 ##

public class Student
       private Long id;
       private String name;

重写Student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;
           Student Student = (Student) o;
           if (!id.equals(Student.id)) return false;
           return name.equals(Student.name);
       }
       @Override
       public int hashCode() {
           int result = id.hashCode();
           result = 19 * result + name.hashCode();
           return result;
       }
     
     
           List<Student> students = Arrays.asList(s1, s2, s3);
           List<Student> studentsNew = new ArrayList<>();
           // 去重
           students.stream().forEach(
                   s -> {
                       if (!studentsNew.contains(s)) {
                           studentsNew.add(s);
                       }
                   }
               );
     
    List的contains()方法实际上是用对象的equals方法去比较

##  三、根据对象的属性去重 ##

Set<Student> studentSet = new TreeSet<>((o1, o2) -> o1.getId().compareTo(o2.getId()));
           studentSet.addAll(students);

Java8写法

List<Student> list = Students.stream().collect(collectingAndThen(toCollection(() -> new TreeSet<>(comparingLong(Student::getId))), ArrayList::new));

##  四、根据对象的属性去重 ##

根据map特性key重复会自动覆盖

Map map = new HashMap();
    list.stream().foreach(it => {
        map.put(it.key,it.value);
    })

最后得到的map及为最后的去重