Set去重会用到

List的remove(obj)方法也会用到 

	@Override
	public boolean equals(Object obj) {
		if (this == obj) {
			return true;
		}
		if (obj == null) {
			return false;
		}
		if (getClass() != obj.getClass()) {
			return false;
		}
		Organ other = (Organ) obj;
		if(id.equals(other.getId())) {
			return true;
		}
		return false; 
	}

	@Override
	public int hashCode() {
		return id == null ? 0 : id.hashCode();
	}

stream去重

@Test
public void listDistinctByStreamDistinct() {
  // 1. 对于 String 列表去重
  List<String> stringList = new ArrayList<String>() {{
    add("A");
    add("A");
    add("B");
    add("B");
    add("C");
  }};

  //去重
  stringList = stringList.stream().distinct().collect(Collectors.toList());

}

 对象去重需要重写hashCode和equals方法

@Test
public void listDistinctByStreamDistinct() throws JsonProcessingException {

    // 1. 对于 Student 列表去重
    List<Student> studentList = getStudentList();
    studentList = studentList.stream().distinct().collect(Collectors.toList());

  }

 根据对象属性字段去重, 借助filter.

定义方法返回函数式接口Predicate ,  参数是函数式接口 Function

private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
    Set<Object> seen = ConcurrentHashMap.newKeySet();
    return t -> seen.add(keyExtractor.apply(t));
}

  @Test
  public void distinctByPropertyTest() throws JsonProcessingException {

    List<Student> studentList = getStudentList();

    studentList = studentList.stream().filter(distinctByKey(Student::getName)).collect(Collectors.toList());

  }