2021-09-21 练习

需求：有5个学生，每个学生有3门课的成绩，从键盘输入以上数据（姓名，三门课成绩），输入的格式：如：zhangsan,30,50,90计算出总成绩，并把学生的信息和计算出的总分数高低顺序存放在磁盘“stu.txt”中
1.描述学生对象
2.定义一个可操作学生对象的工具类
思想：
1.通过获取键盘录入一行数据，并将该行中的信息取出封装成学生对像
2.因为学生有很多，那么就需要存储，使用到集合，因为要对学生的总分排序，所以可以使用TreeSet
3.将集合的信息写入到一个文件中

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;

class Student implements Comparable<Student> {

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

    public int getSum() {
        return sum;
    }

    public String getName() {
        return name;
    }

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

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

    @Override
    public boolean equals(Object obj) {
        if (!(obj instanceof Student)) {
            throw new ClassCastException("不是学生对象");
        }
        Student s = (Student) obj;
        // 名字和总分相同视为同一人
        return this.name.equals(s.name) && this.sum == s.sum;
    }

    @Override
    public int compareTo(Student s) {
        int num = Integer.compare(this.sum, s.sum);
        if (0 == num) {
            return this.name.compareTo(s.name);
        }
        return num;
    }

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

class StudentInfoTool {

    // 默认比较方式
    public static Set<Student> getStudents() throws IOException {
        return getStudents(null);
    }

    public static Set<Student> getStudents(Comparator<Student> cmp) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        Set<Student> stus = null;
        if (null == cmp) {
            stus = new TreeSet<>();
        } else {
            stus = new TreeSet<>(cmp);
        }
        String line;
        while ((line = reader.readLine()) != null) {
            if ("over".equals(line)) {
                break;
            }
            String[] info = line.split(",");
            Student s = new Student(info[0], Integer.parseInt(info[1]), Integer.parseInt(info[2]),
                    Integer.parseInt(info[3]));
            stus.add(s);
        }
        reader.close();
        return stus;
    }

    public static void writeToFile(Set<Student> stus) throws IOException {
        BufferedWriter writer = new BufferedWriter(new FileWriter("stuInfo.txt"));
        for (Student stu : stus) {
            writer.write(stu.toString() + "\t\t");
            writer.write(stu.getSum() + "");
            writer.newLine();
        }
//        writer.flush();
        writer.close();
    }
}

public class StudentInfoTest {

    public static void main(String[] args) throws IOException {
        Comparator<Student> cmp = Collections.reverseOrder(); // 强行逆转比较器
        Set<Student> stus = StudentInfoTool.getStudents(cmp);
        StudentInfoTool.writeToFile(stus);
    }

}