设计类Student和类StudentClass。 (1) 类Student有字符串属性name、double属性grade和int属性age 有带参数的构造方法，可设置三个属性的值 有各个属性的置取方法 要实现Comparable接口 (2)类StudentClass有Set属性stuSet，使用TreeSet存放班级成员，有int属性size存入班级人数。 有createClass()方法: 使用下面三个预置数据的数组，为班级添加成员并设置班级人数。 String names[] = {"Tom","Jerry","Snoopy","Mary","Rose"}; double grades[] = {67,78.5,98,76.5,90}; int ages[] = {17,18,18,19,17}; 有output()方法：实现指定格式的班级成员信息输出 提示：可参考程序21.19。 要求编程实现类Student和类StudentClass，使给定的Test类能正常运行，并实现指定的输出内容。 public class Test { public static void main(String[] args) { StudentClass sClass = new StudentClass(); sClass.createClass(); System.out.println("Original Order:"); System.out.println(sClass.output()); } }

以下是类Student和类StudentClass的代码实现：

import java.util.*;

class Student implements Comparable<Student> {
    private String name;
    private double grade;
    private int age;

    public Student(String name, double grade, int age) {
        this.name = name;
        this.grade = grade;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public double getGrade() {
        return grade;
    }

    public int getAge() {
        return age;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setGrade(double grade) {
        this.grade = grade;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public int compareTo(Student s) {
        if (this.grade > s.getGrade()) {
            return 1;
        } else if (this.grade < s.getGrade()) {
            return -1;
        } else {
            return 0;
        }
    }

    @Override
    public String toString() {
        return "Name: " + name + " Grade: " + grade + " Age: " + age;
    }
}

class StudentClass {
    private Set<Student> stuSet;
    private int size;

    public StudentClass() {
        stuSet = new TreeSet<Student>();
        size = 0;
    }

    public void createClass() {
        String names[] = {"Tom", "Jerry", "Snoopy", "Mary", "Rose"};
        double grades[] = {67, 78.5, 98, 76.5, 90};
        int ages[] = {17, 18, 18, 19, 17};

        for (int i = 0; i < names.length; i++) {
            Student stu = new Student(names[i], grades[i], ages[i]);
            stuSet.add(stu);
            size++;
        }
    }

    public String output() {
        StringBuilder sb = new StringBuilder();
        sb.append("Class Size: " + size + "\n");
        for (Student stu : stuSet) {
            sb.append(stu.toString() + "\n");
        }
        return sb.toString();
    }
}

public class Test {
    public static void main(String[] args) {
        StudentClass sClass = new StudentClass();
        sClass.createClass();
        System.out.println("Original Order:");
        System.out.println(sClass.output());
    }
}

输出结果为：

Original Order:
Class Size: 5
Name: Tom Grade: 67.0 Age: 17
Name: Mary Grade: 76.5 Age: 19
Name: Jerry Grade: 78.5 Age: 18
Name: Rose Grade: 90.0 Age: 17
Name: Snoopy Grade: 98.0 Age: 18