IO_stream_project/Case_module/src/case_package1/Roll_counter.java

package case_package1;

import java.io.*;
import java.util.ArrayList;
import java.util.Arrays;

public class Roll_counter {
    public static void main(String[] args) throws IOException {
        //1、把文件中所有的学生信息读取到内存中
        ArrayList<Student> list = new ArrayList<>();
        BufferedReader br = new BufferedReader(new FileReader("/Users/zhaoxiaoyong/Documents/" +
                "Java/IO_stream_project/Case_module/src/NameInfos.txt"));

        String line;
        while ((line = br.readLine()) != null) {
            String[] arr = line.split("-");
            Student stu = new Student(arr[0], arr[1], Integer.parseInt(arr[2]), Double.parseDouble(arr[3]));
            list.add(stu);
        }
        br.close();

        //2、计算权重的总和
        double weight = 0;
        for (Student student : list) {
            weight += student.getWeight();
        }

        //3、计算每个人的实际占比
        double[] arr = new double[list.size()];
        int index = 0;

        for (Student stu : list) {
            arr[index] = stu.getWeight() / weight;
            index++;
        }
        //System.out.println(Arrays.toString(arr));

        //4、计算每一个人的权重占比范围
        for (int i = 1; i < arr.length; i++) {
            arr[i] += arr[i - 1];
        }
        //System.out.println(Arrays.toString(arr));

        //5、随机抽取
        //获取一个 0.0 ~ 1.0 之间的随机数
        double number = Math.random();
        //判断number在arr中的位置
        //二分查找法：方法返回 -插入点-1
        int result = -Arrays.binarySearch(arr, number) - 1;
        Student stu = list.get(result);
        System.out.println(stu);

        //6、修改当前的学生权限
        double w = stu.getWeight() / 2;
        stu.setWeight(w);

        //7、把集合中的数据再次写到文件中
        BufferedWriter bw = new BufferedWriter(new FileWriter("/Users/zhaoxiaoyong/Documents" +
                "/Java/IO_stream_project/Case_module/src/NameInfos.txt"));
        for (Student s : list) {
            bw.write(s.toString());
            bw.newLine();
        }
        bw.close();
    }
}