假设有10名学生，其中5个男生，5个女生。

要求点到男生的概率为70%，女生的概率为30%。

给男生和女生设置权重，其中男生权重为7，女生权重为3。

public class Test02_case2 {
    public static void main(String[] args) throws IOException {
        //把文件中的学生全部读取出来放到集合中
        ArrayList<String> infoList = new ArrayList<>();
        //使用缓冲流读，因为可以一次读取一行
        BufferedReader br = new BufferedReader(new FileReader("name_10.txt"));
        String info;
        while ((info = br.readLine()) != null) {
            infoList.add(info);
        }
        ArrayList<Student> studentList = new ArrayList<>();
        for (String s : infoList) {
            String[] ss = s.split("-");
            Student student = new Student(ss[0], ss[1], Integer.parseInt(ss[2]),Double.parseDouble(ss[3]));
            studentList.add(student);
        }
        double sum = 0;
        for (Student student : studentList) {
            sum += student.getWeight();
        }
        double p1 = 5 * 7 / sum;
        double p2 = 5 * 3 / sum;
        double r = Math.random();
        int boyCount = 0;
        int girlCount = 0;
        for (int i = 0; i < 1000000; i++) {
            if (r <= 0.3) {
                girlCount++;
            } else {
                boyCount++;
            }
        }
        //统计概率
        double p3 = (double) boyCount / 1000000;
        double p4 = (double) girlCount / 1000000;
        System.out.println(p1);
        System.out.println(p2);

    }
}

public class Test05 {
    public static void main(String[] args) throws IOException {
        //把文件中的学生全部读取出来放到集合中
        ArrayList<String> infoList = new ArrayList<>();
        //使用缓冲流读，因为可以一次读取一行
        BufferedReader br = new BufferedReader(new FileReader("name_10_5.txt"));
        String info;
        while ((info = br.readLine()) != null) {
            infoList.add(info);
        }
        //把属性封装到对象中，并把所有对象放到集合中去
        ArrayList<Student> studentList = new ArrayList<>();
        for (String s : infoList) {
            String[] ss = s.split("-");
            Student student = new Student(ss[0], ss[1], Integer.parseInt(ss[2]), Double.parseDouble(ss[3]));
            studentList.add(student);
        }
        //计算权重总和
        double sum = 0;
        for (Student student : studentList) {
            sum += student.getWeight();
        }
        //概率
        double[] ww = new double[infoList.size()];
        for (int i = 0; i < ww.length; i++) {
            ww[i] = studentList.get(i).getWeight() / sum;
        }
        double[] proRange = new double[ww.length];
        for (int i = 0; i < proRange.length; i++) {
            if (i == 0) {
                proRange[i] = ww[i];
            } else {
                proRange[i] = proRange[i - 1] + ww[i];
            }
        }
        //随机点名
        double r = Math.random();
        System.out.println(r);
        int i = Arrays.binarySearch(proRange, r);
        int index = -(i + 1);
        Student student = studentList.get(index);
        System.out.println(student);

        //将点到的学生权重/2
        student.setWeight(student.getWeight() / 2);
        //
        System.out.println(student);
        //将减半后的权重重新写回
        BufferedWriter bw = new BufferedWriter(new FileWriter("name_10_5.txt"));
        for (Student student1 : studentList) {
            bw.write(student1.getName() + "-" + student1.getGender() + "-" + student1.getAge() + "-" + student1.getWeight());
            bw.newLine();
        }
        bw.close();

    }
}