Java 两种ArrayList集合自定义对象属性排序，Comparator接口 或 Comparable接口

1，Comparator接口 —— 重写Comparator

public class User {

    private String id;
    private String name;

    public User (String id, String name) {
        this.id = id;
        this.name = name;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "User{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                '}';
    }
}

public class ComparatorTest {

    public static void main(String[] args) {
        List list = new ArrayList<>();
        User user1 = new User("222", "张三");
        User user2 = new User("333", "李四");
        User user3 = new User("111", "王五");
        list.add(user1);
        list.add(user2);
        list.add(user3);
        System.out.println("排序前:");
        for (User user : list) {
            System.out.println(user.toString());
        }
        System.out.println("排序后:");
        // 调用排序方法，进行排序
        sortById(list);
        for (User user : list) {
            System.out.println(user.toString());
        }
    }

    /**
     * 根据集合中的对象id，进行升序排序
     */
    public static void sortById(List list) {
        Collections.sort(list, new Comparator() {
            @Override
            public int compare(User u1, User u2) {
                String id1 = u1.getId();
                String id2 = u2.getId();
                // 字符串忽略大小写，进行升序排序
                return id1.compareToIgnoreCase(id2);
            }
        });
    }
}

排序前:
User{id='222', name='张三'}
User{id='333', name='李四'}
User{id='111', name='王五'}
排序后:
User{id='111', name='王五'}
User{id='222', name='张三'}
User{id='333', name='李四'}

 

2，Comparable接口 —— 实体实现Comparable接口，重写compareTo​​​​​​() 方法

public class User implements Comparable{

    private String id;
    private String name;

    public User(String id, String name) {
        this.id = id;
        this.name = name;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "User{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                '}';
    }

    @Override
    public int compareTo(User o) {
        return this.id.compareToIgnoreCase(o.getId());
    }
}

public class ComparatorTest {

    public static void main(String[] args) {
        List list = new ArrayList<>();
        User user1 = new User("222", "张三");
        User user2 = new User("333", "李四");
        User user3 = new User("111", "王五");
        list.add(user1);
        list.add(user2);
        list.add(user3);
        System.out.println("排序前:");
        for (User user : list) {
            System.out.println(user.toString());
        }
        System.out.println("排序后:");
        // 进行集合排序
        Collections.sort(list);
        for (User user : list) {
            System.out.println(user.toString());
        }
    }
}

排序前:
User{id='222', name='张三'}
User{id='333', name='李四'}
User{id='111', name='王五'}
排序后:
User{id='111', name='王五'}
User{id='222', name='张三'}
User{id='333', name='李四'}