int binarySearch(double[] a, double key) 

package com.prettyspiderList.train;
/**
 * @author prettyspider
 * @ClassName Student
 * @description: TODO
 * @date 2023/8/4 17:28
 * @Version V1.0
 */
public class Student {
    private String name;
    private int age;
    public Student() {
    }
    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
    /**
     * 獲取
     * @return name
     */
    public String getName() {
        return name;
    }
    /**
     * 設(shè)置
     * @param name
     */
    public void setName(String name) {
        this.name = name;
    }
    /**
     * 獲取
     * @return age
     */
    public int getAge() {
        return age;
    }
    /**
     * 設(shè)置
     * @param age
     */
    public void setAge(int age) {
        this.age = age;
    }
    public String toString() {
        return "Student{name = " + name + ", age = " + age + "}";
    }
}

package com.prettyspiderList.Map.train;
import java.io.*;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Random;
/**
 * @author prettyspider
 * @ClassName test04
 * @description: TODO
 * @date 2023/9/7 21:35
 * @Version V1.0
 */
public class test04 {
    /**
     * txt文件中事先準(zhǔn)備號一些學(xué)生信息，每個學(xué)生的信息獨占一行
     * 要求1：
     *      每次被點到的學(xué)生，再次被點到的概率再原先的基礎(chǔ)上降低一半
     *      舉例： 80個學(xué)生，點名2次，每次都點到a，概率變化
     *      1： 1.25&
     *      2.a 0.625% 其他人1.2579%
     */
    public static void main(String[] args) throws IOException {
        /**
         * 帶權(quán)重的隨機算法：
         *      根據(jù)總權(quán)重，獲取每個對象的占比
         *
         */
        //創(chuàng)建student集合
        ArrayList<Student> list = new ArrayList<>();
        // 創(chuàng)建輸入流
        BufferedReader reader = new BufferedReader(new FileReader(".\\com\\prettyspiderList\\Map\\train\\stu.txt"));
        String line;
        while ((line = reader.readLine()) != null) {
            String[] arr = line.split("-");
            list.add(new Student(arr[0], arr[1], Integer.parseInt(arr[2]), Double.valueOf(arr[3])));
        }
        // 關(guān)流
        reader.close();
        //計算權(quán)重
        // 1.獲取總權(quán)重
        double weight = 0.0;
        for (Student stu : list) {
            weight += stu.getWeight();
        }
        // 2.獲取單個權(quán)重
        double[] wightArr = new double[list.size()];
        for (int i = 0; i < list.size(); i++) {
            wightArr[i] = list.get(i).getWeight() / weight;
        }
        System.out.println(Arrays.toString(wightArr));
        // 每個的權(quán)重占比，其前面一個的權(quán)重加自己的權(quán)重, 表示的是在這個范圍內(nèi)是對應(yīng)的對象
        for (int i = 1; i < wightArr.length; i++) {
            wightArr[i] = wightArr[i] + wightArr[i - 1];
        }
        System.out.println(Arrays.toString(wightArr));
        // 隨機生成一個0-1之間的隨機數(shù)
        Random random = new Random();
        double key = random.nextDouble(1);
        System.out.println(key);
        // 二分查找法：方法返回： 結(jié)果=-插入點-1
        // 則插入點=-結(jié)果-1
        int index = -Arrays.binarySearch(wightArr, key) -1;
        // 對獲取到的對象的權(quán)重減半
        double num = list.get(index).getWeight() / 2;
        list.get(index).setWeight(num);
        System.out.println(list.get(index));
        // 將數(shù)據(jù)協(xié)會到文件中
        BufferedWriter writer = new BufferedWriter(new FileWriter(".\\com\\prettyspiderList\\Map\\train\\stu.txt"));
        for (Student student : list) {
            writer.write(student.toString());
            writer.newLine();
        }
        // 關(guān)閉流
        writer.close();
    }
}