练习：存储学生信息

package exercise;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Collections;
import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;

//学生类，实现Comparable接口，能够比较
class Student implements Comparable {

    private String name;
    private int ma, cn, en;
    private int sum;

    Student(String name, int ma, int cn, int en) {
        this.name = name;
        this.ma = ma;
        this.cn = cn;
        this.en = en;
        sum = ma + cn + en;
    }

    public String getName() {
        return name;
    }

    public int getSum() {
        return sum;
    }

    public int hashCode() {
        return name.hashCode() + sum * 78;
    }

    public boolean equals(Object obj) {
        if (!(obj instanceof Student))
            throw new ClassCastException("类型不匹配");
        Student s = (Student) obj;
        return this.name.equals(s.name) && this.sum == s.sum;
    }

    //覆盖compareTo方法
    @Override
    public int compareTo(Student s) {
        int num = new Integer(this.sum).compareTo(new Integer(s.sum));
        if (num == 0)
            return this.name.compareTo(s.name);
        return num;
    }

    public String toString() {
        return "student[" + name + ", " + ma + ", " + cn + ", " + en + "]";
    }
}

//工具类
class StudentInfoTool {

    public static Set getStudents() throws IOException {
        return getStudents(null);
    }

    //Comparator比较器
    public static Set getStudents(Comparator cmp)
            throws IOException {
        BufferedReader bufr = new BufferedReader(new InputStreamReader(
                System.in));

        String line = null;
        Set stus = null;
        if (cmp == null) {
            stus = new TreeSet();
        } else {
            stus = new TreeSet(cmp);
        }
        while ((line = bufr.readLine()) != null) {
            if ("over".equals(line))
                break;
            String[] info = line.split(",");
            Student stu = new Student(info[0], Integer.parseInt(info[1]),
                    Integer.parseInt(info[2]), Integer.parseInt(info[3]));
            stus.add(stu);
        }

        bufr.close();
        return stus;
    }

    //写入文件方法
    public static void write2File(Set stus) throws IOException {
        BufferedWriter bufw = new BufferedWriter(new FileWriter("stuinfo.txt"));
        for (Student stu : stus) {
            bufw.write(stu.toString() + "\t");
            bufw.write(stu.getSum() + "");
            bufw.newLine();
            bufw.flush();
        }
        bufw.close();
    }
}

public class StudentInfoTest {

    public static void main(String[] args) throws IOException {

        // 按照成绩递增
        Set stus1 = StudentInfoTool.getStudents();

        // 按照成绩递减
        Comparator cmp = Collections.reverseOrder();
        Set stus2 = StudentInfoTool.getStudents(cmp);

        StudentInfoTool.write2File(stus2);
    }
}