Comparator接口在Java中的使用场景

在Java中，Comparator接口主要用于定义对象之间的排序规则。它通常用于集合类（如List）和数组的排序操作。以下是一些常见的使用场景：

1. 对集合进行排序

当你需要对一个集合（如ArrayList、LinkedList等）中的元素进行排序时，可以使用Collections.sort()方法，并传入一个实现了Comparator接口的对象。

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

class Person {
    String name;
    int age;

    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));

        // 按年龄排序
        Collections.sort(people, new Comparator<Person>() {
            @Override
            public int compare(Person p1, Person p2) {
                return Integer.compare(p1.age, p2.age);
            }
        });

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

2. 使用Lambda表达式简化代码

从Java 8开始，你可以使用Lambda表达式来简化Comparator的实现。

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

class Person {
    String name;
    int age;

    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));

        // 使用Lambda表达式按年龄排序
        Collections.sort(people, (p1, p2) -> Integer.compare(p1.age, p2.age));

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

3. 多条件排序

你可以通过组合多个Comparator来实现多条件排序。

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

class Person {
    String name;
    int age;
    double salary;

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

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

public class Main {
    public static void main(String[] args) {
        List<Person> people = new ArrayList<>();
        people.add(new Person("Alice", 30, 50000));
        people.add(new Person("Bob", 25, 60000));
        people.add(new Person("Charlie", 30, 55000));

        // 先按年龄排序，再按薪水排序
        Collections.sort(people, Comparator.comparingInt(Person::getAge)
                                       .thenComparingDouble(Person::getSalary));

        System.out.println(people); // 输出: [Bob (25, 60000.0), Alice (30, 50000.0), Charlie (30, 55000.0)]
    }
}

4. 自定义排序逻辑

你可以根据具体需求实现自定义的排序逻辑。

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

class Person {
    String name;
    int age;

    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));

        // 按名字长度排序
        Collections.sort(people, Comparator.comparingInt(person -> person.name.length()));

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

通过这些示例，你可以看到Comparator接口在Java中的多种使用场景，它提供了一种灵活且强大的方式来定义对象的排序规则。