String filePath = "用戶信息.txt";
                User modifyFile = new User();
                System.out.println("請(qǐng)輸入原密碼：");
                String oldString = sc.next();
                //如果輸入的原密碼不正確，無(wú)法進(jìn)行修改，如果正確，才能進(jìn)行修改
                if (oldString.equals(userinf[1])) {
                    System.out.println("請(qǐng)輸入新密碼：");
                    String newString = sc.next();
                    boolean result = modifyFile.writeFile(filePath, modifyFile.readFileContent(userinf, filePath, userinf[1], newString));// 修改文件中密碼

//            如果修改結(jié)果為true，進(jìn)行修改成功提示，否則提示修改失敗
                    if (result == true) {
                        System.out.println("修改成功，請(qǐng)重新登錄！");
                        return;
                    } else {
                        System.out.println("修改錯(cuò)誤，請(qǐng)檢查后重新修改！");
                    }
                } else {
                    System.out.println("輸入錯(cuò)誤，請(qǐng)檢查后重新進(jìn)行修改！");
                }

modifyFile.writeFile(filePath, modifyFile.readFileContent(userinf, filePath, userinf[1], newString));// 修改文件中密碼

// 讀文件
    public String readFileContent(String[] userinf, String filePath, String oldString, String newString) {
        Scanner sc = new Scanner(System.in);
        BufferedReader br = null;
        String line = null;
        StringBuffer bufAll = new StringBuffer();// 保存修改過(guò)后的所有內(nèi)容
        try {
            br = new BufferedReader(new InputStreamReader(new FileInputStream(filePath), "UTF-8"));

            while ((line = br.readLine()) != null) {
                StringBuffer buf = new StringBuffer();
                // 修改內(nèi)容核心代碼
                String[] userinf2 = line.split(",");
                if (userinf2[0].equals(userinf[0])) {//判斷條件根據(jù)自己的要求修改
                    buf.append(line);
                    int indexOf = line.indexOf(oldString);
                    buf.replace(indexOf, indexOf + oldString.length(), newString);// 修改內(nèi)容
                    buf.append(System.getProperty("line.separator"));// 添加換行
                    bufAll.append(buf);
                } else {
                    buf.append(line);
                    buf.append(System.getProperty("line.separator"));
                    bufAll.append(buf);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (br != null) {
                try {
                    br.close();
                } catch (Exception e) {
                    br = null;
                }
            }
        }
        return bufAll.toString();
    }

    // 寫文件
    public boolean writeFile(String filePath, String content) {
        BufferedWriter bw = null;
        try {
            bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(filePath), "UTF-8"));
            bw.write(content);
            bw.flush();
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        } finally {
            if (bw != null) {
                try {
                    bw.close();
                } catch (IOException e) {
                    bw = null;
                }
            }
        }
        return true;
    }