Comparable和Comparator

0.简介

Comparable和Comparator都用于同种类型对象比较，集合排序 

1.Comparator

@AllArgsConstructor
@ToString
public class User {
    @Setter @Getter
    private String name;

    @Setter @Getter
    private Integer age;
}

public static void main(String[] args) {
    List<User> userList = new ArrayList<>();
    userList.add(new User("a", 12));
    userList.add(new User("b", 12));
    userList.add(new User("c", 20));
    userList.add(new User("d", 2));

    // 升序
    Collections.sort(userList, Comparator.comparingInt(User::getAge));
    System.out.println(userList.toString());

    // 降序
    Collections.sort(userList, (user1, user2) -> user2.getAge() - user1.getAge());
    System.out.println(userList.toString());
}

2.Comparable

// 升序
@AllArgsConstructor
@ToString
public class UserAsc implements Comparable<UserAsc> {
    @Setter @Getter
    private String name;

    @Setter @Getter
    private Integer age;

    @Override
    public int compareTo(UserAsc userAsc) {
        return this.age - userAsc.getAge();
    }
}

public static void main(String[] args) {
    List<UserAsc> userAscList = new ArrayList<>();
    userAscList.add(new UserAsc("a", 12));
    userAscList.add(new UserAsc("b", 12));
    userAscList.add(new UserAsc("c", 20));
    userAscList.add(new UserAsc("d", 2));

    Collections.sort(userAscList);
    System.out.println(userAscList.toString());
}


// 降序
@AllArgsConstructor
@ToString
public class UserDesc implements Comparable<UserDesc> {
    @Setter @Getter
    private String name;

    @Setter @Getter
    private Integer age;

    @Override
    public int compareTo(UserDesc userAsc) {
        return userAsc.getAge() - this.age;
    }
}

public static void main(String[] args) {
    List<UserDesc> userDescList = new ArrayList<>();
    userDescList.add(new UserDesc("a", 12));
    userDescList.add(new UserDesc("b", 12));
    userDescList.add(new UserDesc("c", 20));
    userDescList.add(new UserDesc("d", 2));

    // desc
    Collections.sort(userDescList);
    System.out.println(userDescList.toString());
}