题目要求：

1.可以往一个文本文档中写入员工信息：name，id和详情

2.可以更改name

package FanCQ.Xue.practice;

import java.io.*;
import java.util.Scanner;

/*
 * @author XueWeiWei
 * @date 2019/3/31 20:13
 */
public class Xue_RW {
    public static void main(String[] args) throws IOException {
        //创建一个文本文件，如果已经存在，则告知用户：The file was created
        File file = new File("./demo.txt");
        if (file.exists()){
            System.out.println("The file was created.");
        }else {
            file.createNewFile();
        }
        RandomAccessFile randomAccessFile = new RandomAccessFile("./demo.txt","rw");   //使用RandomAccessFile类对文件进行随意修改
        //让用户进行操作选择（1.往文本文件中插入数据；2.修改文本文件的数据；0.退出该程序）
        System.out.println("插入，输入1");
        System.out.println("修改，输入2");
        System.out.println("退出，输入0");
        System.out.println("输入你的选择：");
        Scanner scanner = new Scanner(System.in);
        int choose = Integer.parseInt(scanner.next());
        XWW xww = new XWW();                               //初始化要写入文件的类
        int i=0;                                           //使用变量i来记录文本文件的行数
        //使用BufferedReader来进行文件的按行读取
        FileReader fileReader = new FileReader("./demo.txt");
        BufferedReader bufferedReader = new BufferedReader(fileReader);
        StringBuilder sh = new StringBuilder();   //使用StringBuilder来将读取的数据填充到一个字符串内，容易进行查找与修改
        String[] str = new String[20];            //使用数组str[]将文本文件的每一行数据进行存储，放到StringBuilder中
        while ( ( str[i] = bufferedReader.readLine() ) != null){
            sh.append(str[i]);
            i++;
        }
//        System.out.println("i的值："  + i);
        do {
            if (choose == 1){
                //如果是初次写入数据，将指标放到文件开头，放到文件末尾
                if (i>0){
                    randomAccessFile.seek(randomAccessFile.length());
                }else {
                    randomAccessFile.seek(0);
                }
                //输入类的三个信息，并进行写入
                System.out.println("name：");
                String name = scanner.next();
                System.out.println("id:");
                String id = String.valueOf(scanner.next());
                System.out.println("text:");
                String text = scanner.next();
                xww.setName(name);
                xww.setId(id);
                xww.setText(text);
                xww.write(randomAccessFile);
                //写入一行，增加一行数据
                i++;
                //同时stringBuilder中也要增加数据
                sh.append(name).append(id).append(text);
            }
            if (choose == 2){
                System.out.println("当前一共" +(i) + "行数据");
                System.out.println("输入你想修改的数据name：");
                String s =  scanner.next();
                System.out.println("输入你想修改后的数据name(请输入和想修改name的信息等长！！！！)：");
                String s1 =  scanner.next();
                System.out.println("字符串的位置" + sh.indexOf(s));
                System.out.println(sh);
                //使用start来查找到想要修改数据的位置
                int start = sh.indexOf(s);
                if (start == -1){
                    System.out.println("您所想要修改的数据不存在");
                }else {
//                    if (s.length()<=s1.length()){
                        randomAccessFile.seek(start);
                        xww = new XWW(s1,"","");
                        xww.write2(randomAccessFile);
//                    }else {}
                }
            }
            System.out.println("输入你的选择：");
            choose = Integer.parseInt(scanner.next());
        }while (choose != 0);

        bufferedReader.close();
        fileReader.close();
//        XWW xww0 = new XWW("薛卫卫","110","我是16智71班薛卫卫");
//        randomAccessFile.seek(0);
//        xww0.write(randomAccessFile);
//
//        String name = scanner.next();
//        xww0.setName(name);
//        xww0.write(randomAccessFile);
//        randomAccessFile.seek(0);
//
//        XWW xww1 = new XWW();
//        xww1.read(randomAccessFile);
//        System.out.println(xww1.name + " " + xww1.id + " " + xww1.text);
    }
}
class XWW{
    public String name;
    public String id;
    public String text;

    public XWW() {
    }

    public XWW(String name, String id, String text) {
        this.name = name;
        this.id = id;
        this.text = text;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }

    //将三个数据进行写入，同时换行
    public void write(RandomAccessFile randomAccessFile) throws IOException {
        randomAccessFile.writeUTF(name);
        randomAccessFile.writeUTF(id);
        randomAccessFile.writeUTF(text);
        randomAccessFile.writeUTF("\n");
    }

    //将三个数据读取文件
    public void read(RandomAccessFile randomAccessFile) throws IOException {
        this.name=randomAccessFile.readUTF();
        this.id=randomAccessFile.readUTF();
        this.text=randomAccessFile.readUTF();
    }
    //修改名字
    public void write2(RandomAccessFile randomAccessFile) throws IOException {
        randomAccessFile.writeUTF(name);
    }
}