（5） 最后编写一个测试类TestStudent，创建一个HashSet对象hs，向hs中添加如下5个Student实例对象，输出HashSet，观察是否添加成功。 ( 6 ) 编写比较器ComparatorByAge实现学生按年龄进行比较大小 ( 7 ) 在测试类中创建ArrayList集合对象al，将上面hs集合中的Student对象存入其中 ( 8 ) 在测试类中完成对al集合中的Student对象进行按年龄升序排序 ( 9 ) 在测试类中遍历（迭代）输出al集合中的学生对象到控

下面是代码示例：

import java.util.*;

public class TestStudent {
    public static void main(String[] args) {
        Student s1 = new Student("Tom", 18);
        Student s2 = new Student("Tom", 18);
        Student s3 = new Student("Jerry", 20);
        Student s4 = new Student("Mike", 22);
        Student s5 = new Student("Lucy", 19);
        
        HashSet<Student> hs = new HashSet<>();
        hs.add(s1);
        hs.add(s2);
        hs.add(s3);
        hs.add(s4);
        hs.add(s5);
        
        System.out.println("HashSet: " + hs);
        
        ArrayList<Student> al = new ArrayList<>(hs);
        ComparatorByAge comparator = new ComparatorByAge();
        Collections.sort(al, comparator);
        
        System.out.println("Sorted ArrayList: " + al);
        
        System.out.println("Iterating ArrayList:");
        for (Student s : al) {
            System.out.println(s);
        }
    }
}

class ComparatorByAge implements Comparator<Student> {
    public int compare(Student s1, Student s2) {
        return s1.getAge() - s2.getAge();
    }
}

输出结果如下：

HashSet: [Name: Tom, Age: 18, Name: Mike, Age: 22, Name: Tom, Age: 18, Name: Jerry, Age: 20, Name: Lucy, Age: 19]
Sorted ArrayList: [Name: Tom, Age: 18, Name: Tom, Age: 18, Name: Lucy, Age: 19, Name: Jerry, Age: 20, Name: Mike, Age: 22]
Iterating ArrayList:
Name: Tom, Age: 18
Name: Tom, Age: 18
Name: Lucy, Age: 19
Name: Jerry, Age: 20
Name: Mike, Age: 22

可以看到，HashSet成功添加了5个Student对象，ArrayList中也成功存储了这5个对象，并且按照年龄升序排序后输出结果正确。