java在txt里怎么更新数据啊

Question

这是一个模拟atm的 一行三个值 分别是账户 密码 和余额
我可以从txt里读出数据 就是不知道取了钱、存了钱以后我该怎么更新txt里的数据

 package atm;

/**
 * Created by lenovo on 2016/5/5.
 */
import java.awt.List;

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

public class c {
    public static void readTxtFile(String filePath){
        try {
            String encoding="GBK";
            File file=new File(filePath);


            if(file.isFile() && file.exists()){ //判断文件是否存在
                InputStreamReader read = new InputStreamReader(
                        new FileInputStream(file),encoding);//考虑到编码格式
                BufferedReader bufferedReader = new BufferedReader(read);
                String lineTxt = null;
                int line=1;
                Scanner sc = new Scanner(System.in);
                System.out.println("请输入账户");

                int a=sc.nextInt();
                HashMap m=new HashMap();
                while((lineTxt = bufferedReader.readLine())!= null){
                    String[] lin=lineTxt.split(" ");
                    m.put(lin[0]+lin[1],lin[2]);
                    int zh=Integer.parseInt(lin[0]);
                    int mm=Integer.parseInt(lin[1]);
                    if(a==zh){
                        System.out.println("请输入密码");
                        int b=sc.nextInt();
                        if(b==mm){


                            int g=0;
                            while(g<4) {
                                int money = Integer.parseInt(lin[2]);
                                System.out.println("1.查看余额\n2.取款\n3.存款\n4.退出\n");

                                int c=sc.nextInt();
                                {
                                    switch (c) {
                                        case 1:
                                            System.out.println("您账户内余额为：" + money);
                                            g = 1;
                                            break;
                                        case 2:
                                            System.out.println("输入您要取的金额：");
                                            int d = sc.nextInt();
                                            if (d > money) {
                                                System.out.println("余额不足！");
                                                g = 2;
                                            } else {
                                                money -= d;
                                                System.out.println("您账户内余额为：" + money);
                                                g = 2;
                                            }
                                            break;

                                        case 3:
                                            System.out.println("请输入你要存的金额：");
                                            int e = sc.nextInt();
                                            money += e;
                                            System.out.println("您账户内余额为：" + money);
                                            g = 3;
                                            break;
                                        case 4:break;
                                        default:
                                            System.out.println("1.查看余额\n2.取款\n3.存款\n4.退出\n");
                                            g = sc.nextInt();
                                            return;
                                    }


                                }

                            }
                        }
                        else
                        {
                            System.out.println("您输入的密码错误");
                        }
                    }else{
                        System.out.println("您输入的账户不存在");
                    }
                }
                read.close();
            }else{
                System.out.println("找不到指定的文件");
            }
        }
        catch (Exception e) {
            System.out.println("读取文件内容出错");
            e.printStackTrace();
        }

    }


    public static void main(String arg[]){
        String filePath = "C:\\Users\\lenovo\\Desktop\\11.txt";

        readTxtFile(filePath);
    }



}

Answer 1

 public class c {
    public static void readTxtFile(String filePath){
        try {
            String encoding="GBK";
            File file=new File(filePath);


            if(file.isFile() && file.exists()){ //判断文件是否存在
                InputStreamReader read = new InputStreamReader(
                        new FileInputStream(file),encoding);//考虑到编码格式
                BufferedReader bufferedReader = new BufferedReader(read);
                String lineTxt = null;
                int line=1;
                System.out.println("请输入账户");
                Scanner sc = new Scanner(System.in);

                int a=sc.nextInt();
                HashMap m=new HashMap();

                ArrayList<String> lineList = new ArrayList();
                boolean isOper = false;//是否做存款取款动作了，钱没变化就没必要写文件了
                boolean isLogined = false;//是否已经登录过，登陆过就不用再循环找是否还有相同用户了
                while((lineTxt = bufferedReader.readLine())!= null){//先把文件读出来
                    lineList.add(lineTxt);
                }
                bufferedReader.close();
                read.close();
                for(int i=0;i<lineList.size()&&!isLogined;i++){
                    lineTxt = lineList.get(i);
                    String[] lin=lineTxt.split(" ");
                    m.put(lin[0]+lin[1],lin[2]);
                    int zh=Integer.parseInt(lin[0]);
                    int mm=Integer.parseInt(lin[1]);
                    if(a==zh){
                        System.out.println("请输入密码");
                        int b=sc.nextInt();
                        if(b==mm){
                            isLogined = true;
                            int g=0;
                            while(g<4) {
                                int money = Integer.parseInt(lin[2]);
                                System.out.println("1.查看余额\n2.取款\n3.存款\n4.退出\n");

                                g=sc.nextInt();
                                {
                                    switch (g) {
                                        case 1:
                                            System.out.println("您账户内余额为：" + money);
                                            break;
                                        case 2:
                                            System.out.println("输入您要取的金额：");
                                            int d = sc.nextInt();
                                            if (d > money) {
                                                System.out.println("余额不足！");
                                            } else {
                                                money -= d;
                                                System.out.println("您账户内余额为：" + money);
                                            }
                                            lin[2] = money+"";//这里需要重新赋值
                                            isOper = true;
                                            break;

                                        case 3:
                                            System.out.println("请输入你要存的金额：");
                                            int e = sc.nextInt();
                                            money += e;
                                            System.out.println("您账户内余额为：" + money);
                                            lin[2] = money+"";//这里需要重新赋值
                                            isOper = true;
                                            break;
                                        case 4:
                                            lineTxt = lin[0] + " " +  lin[1] + " " +  lin[2];
                                            lineList.set(i, lineTxt);//更新余额
                                            break;
                                        default:
                                            System.out.println("1.查看余额\n2.取款\n3.存款\n4.退出\n");
                                            g = sc.nextInt();
                                    }


                                }

                            }
                        }
                        else
                        {
                            System.out.println("您输入的密码错误");
                        }
                    }else{
                        System.out.println("您输入的账户不存在");
                    }
                }
                if(isOper){//写文件
                    FileWriter fw = new FileWriter(file);
                    //遍历clist集合写入到fileName中
                    for (String str: lineList){
                        fw.write(str);
                        fw.write("\n");
                    }
                    //刷新缓冲区
                    fw.flush();
                    //关闭文件流对象
                    fw.close();
                }
            }else{
                System.out.println("找不到指定的文件");
            }
        }
        catch (Exception e) {
            System.out.println("读取文件内容出错");
            e.printStackTrace();
        }

    }


    public static void main(String arg[]){
        String filePath = "C:\\11.txt";

        readTxtFile(filePath);
    }



}