如何用Comparator对List进行排序

在Java中，您可以使用Comparator接口对List进行排序。以下是一些示例：

1. 对整数列表进行升序排序：

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<Integer> numbers = new ArrayList<>();
        numbers.add(5);
        numbers.add(3);
        numbers.add(1);
        numbers.add(4);
        numbers.add(2);

        Collections.sort(numbers, new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o1.compareTo(o2);
            }
        });

        System.out.println(numbers); // 输出: [1, 2, 3, 4, 5]
    }
}

2. 对字符串列表进行字母顺序排序：

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> words = new ArrayList<>();
        words.add("apple");
        words.add("banana");
        words.add("cherry");
        words.add("date");

        Collections.sort(words, new Comparator<String>() {
            @Override
            public int compare(String o1, String o2) {
                return o1.compareTo(o2);
            }
        });

        System.out.println(words); // 输出: [apple, banana, cherry, date]
    }
}

3. 对自定义对象列表进行排序：

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

class Person {
    String name;
    int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return name + " (" + age + ")";
    }
}

public class Main {
    public static void main(String[] args) {
        List<Person> people = new ArrayList<>();
        people.add(new Person("Alice", 30));
        people.add(new Person("Bob", 25));
        people.add(new Person("Charlie", 35));

        Collections.sort(people, new Comparator<Person>() {
            @Override
            public int compare(Person o1, Person o2) {
                return Integer.compare(o1.age, o2.age);
            }
        });

        System.out.println(people); // 输出: [Bob (25), Alice (30), Charlie (35)]
    }
}

从Java 8开始，您可以使用lambda表达式简化Comparator的实现：

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> words = new ArrayList<>();
        words.add("apple");
        words.add("banana");
        words.add("cherry");
        words.add("date");

        words.sort(Comparator.naturalOrder());

        System.out.println(words); // 输出: [apple, banana, cherry, date]
    }
}