一、嵌套对象倒序的正确书写方式
描述：对象A内部封装对象B，根据B的字段做倒排
Comparator<User> ageDescCom = Comparator.comparing(temp -> temp.getKid().getAge()).reversed();//报错：temp为object
Comparator<User> ageDescCom = Comparator.comparing((User temp) -> temp.getKid().getAge()).reversed();//有效
Comparator<User> ageDescCom = Comparator.comparing(temp -> temp.getKid().getAge(), Comparator.reverseOrder());//有效测试代码：
@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class User extends BaseEntity {
String nickname;
String avatar;
Integer gender;
Integer age;
User kid;
@Override
public User instance() {
return new User();
}
}
public class ComparatorTest {
@Test
public void test() {
User kid = User.builder().age(1).build();
User kid1 = User.builder().age(2).build();
User kid2 = User.builder().age(3).build();
User kid3 = User.builder().age(4).build();
User kid4 = User.builder().age(5).build();
User user = User.builder().kid(kid).build();
User user1 = User.builder().kid(kid1).build();
User user2 = User.builder().kid(kid2).build();
User user3 = User.builder().kid(kid3).build();
User user4 = User.builder().kid(kid4).build();
List<User> list = Arrays.asList(user2,user3,user1,user,user4);
System.out.println(list);
//Comparator<User> ageDescCom = Comparator.comparing(temp -> temp.getKid().getAge()).reversed();//报错：temp为object
//Comparator<User> ageDescCom = Comparator.comparing((User temp) -> temp.getKid().getAge()).reversed();//有效
//Comparator<User> ageDescCom = Comparator.comparing(temp -> temp.getKid().getAge(), Comparator.reverseOrder());//有效
list = list.stream().sorted(ageDescCom).collect(Collectors.toList());
System.out.println(list);
}
}二、多层/嵌套/多重条件排序
描述：如：先按照年龄正序，同年龄按照体重倒序。
Comparator<XXX> A = Comparator.comparing(XXX::getAge).reversed(); Comparator<XXX> B = Comparator.comparing(XXX::getWeight); Comparator<XXX> C = A.thenComparing(B);
测试代码：
public class ComparatorTest {
@Test
public void test2() {
User kid = User.builder().age(4).weight(1).build();
User kid1 = User.builder().age(4).weight(2).build();
User kid2 = User.builder().age(4).weight(3).build();
User kid3 = User.builder().age(4).weight(4).build();
User kid4 = User.builder().age(4).weight(5).build();
User user = User.builder().age(20).kid(kid).build();
User user1 = User.builder().age(20).kid(kid1).build();
User user2 = User.builder().age(20).kid(kid2).build();
User user3 = User.builder().age(20).kid(kid3).build();
User user4 = User.builder().age(20).kid(kid4).build();
List<User> list = Arrays.asList(user2,user3,user1,user,user4);
System.out.println(list);
Comparator<User> userAgeAscCom = Comparator.comparing(User::getAge);
Comparator<User> kidAgeAscCom = Comparator.comparing(User::getAge);
Comparator<User> kidWeightDescCom = Comparator.comparing(temp -> temp.getKid().getWeight(), Comparator.reverseOrder());
Comparator<User> userAgeAscThenKidWeightDescCom = userAgeAscCom.thenComparing(kidWeightDescCom);//父母年龄正序后小孩体重倒序
Comparator<User> kidAgeAscThenKidWeightDescCom = kidAgeAscCom.thenComparing(kidWeightDescCom);//小孩年龄正序后小孩体重倒序
list = list.stream().sorted(userAgeAscThenKidWeightDescCom).collect(Collectors.toList());
System.out.println(list);
list = list.stream().sorted(kidAgeAscThenKidWeightDescCom).collect(Collectors.toList());
System.out.println(list);
}
}