import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
 
public class TestUtil {
    public static void main(String[] args) {
        Student stu1 = new Student("小米", 1);
        Student stu2 = new Student("小王", 2);
        Student stu3 = new Student("小明", 3);
 
        List<Student> list = new ArrayList<>();
        list.add(stu2);
        list.add(stu1);
        list.add(stu3);
 
        System.out.println("排序前：");
        System.out.println(list);
 
        System.out.println("排序后：");
        Collections.sort(list, new Comparator<Student>() {
            @Override
            public int compare(Student stu1, Student stu2) {
                return stu1.getAge() - stu2.getAge();
            }
        });
        System.out.println(list);
    }
}

簡(jiǎn)寫方式：

list.sort((l1,l2) -> l1-l2);