Java 中的排序Comparable 与 Comparator 的使用与区别对比解析

public class CompareToDemo {
    public static void main(String[] args) {
        // String 按字典序比较
        System.out.println("apple".compareTo("banana")); // -1
        System.out.println("dog".compareTo("dog"));      // 0
        System.out.println("zoo".compareTo("apple"));    // 正数
        // Integer 按数值大小比较
        Integer a = 10, b = 20;
        System.out.println(a.compareTo(b)); // -1
        System.out.println(b.compareTo(a)); // 1
        System.out.println(a.compareTo(10));// 0
    }
}

public interface Comparable<T> {
    int compareTo(T o);
}

public interface Comparator<T> {
    int compare(T o1, T o2);
}

class Student implements Comparable<Student> {
    private String name;
    private int age;
    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
    // 定义“自然顺序”：按年龄升序
    @Override
    public int compareTo(Student other) {
        return Integer.compare(this.age, other.age);
    }
    @Override
    public String toString() {
        return name + "(" + age + ")";
    }
}
public class ComparableDemo {
    public static void main(String[] args) {
        List<Student> list = new ArrayList<>();
        list.add(new Student("Alice", 22));
        list.add(new Student("Bob", 18));
        list.add(new Student("Charlie", 20));
        // 使用 Comparable 定义的 compareTo 方法排序
        Collections.sort(list);
        System.out.println(list); 
        // 输出: [Bob(18), Charlie(20), Alice(22)]
    }
}

Collections.sort(list, new Comparator<Student>() {
    @Override
    public int compare(Student s1, Student s2) {
        return Integer.compare(s1.getAge(), s2.getAge());
    }
});

list.sort((s1, s2) -> Integer.compare(s1.getAge(), s2.getAge()));

list.sort(Comparator.comparing(Student::getAge));

[Bob(18), Charlie(20), Alice(22)]

//方式一、方法引用 + 链式 Comparator
list.sort(
    Comparator.comparing(Student::getAge)
              .thenComparing(Student::getName)
);
//方式二、匿名内部类写法
list.sort(new Comparator<Student>() {
    @Override
    public int compare(Student s1, Student s2) {
        // 先按年龄排序
        int result = Integer.compare(s1.getAge(), s2.getAge());
        // 如果年龄相同，则按姓名排序
        if (result == 0) {
            result = s1.getName().compareTo(s2.getName());
        }
        return result;
    }
});
//方式三、Lambda 表达式写法（Java 8+ 推荐）
list.sort((s1, s2) -> {
    int result = Integer.compare(s1.getAge(), s2.getAge());
    if (result == 0) {
        result = s1.getName().compareTo(s2.getName());
    }
    return result;
});

public class Student implements Comparable<Student> {
    private int age;
    private String name;
    @Override
    public int compareTo(Student other) {
        // 先按年龄，再按姓名
        int result = Integer.compare(this.age, other.age);
        if (result == 0) {
            result = this.name.compareTo(other.name);
        }
        return result;
    }
}

Comparator<Student> byAgeThenName = 
    Comparator.comparing(Student::getAge)
              .thenComparing(Student::getName);
Comparator<Student> byNameThenAge = 
    Comparator.comparing(Student::getName)
              .thenComparing(Student::getAge);