我的妈耶，C:\\Users\\prnck\\AndroidStudioProjects\\Demo\\info.textzh这不是手机的啊

n你需要拿手机的路径才行。

Environment.getExternalStorageState()
w外部的，可以看看Environment

r如果是app内部安装目录，可以用context getCache，等等来写文件，这个不用权限的

代码：

package com.example.demo;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

import androidx.appcompat.app.AppCompatActivity;

import java.io.File;
import java.io.FileOutputStream;

public class QQLogin extends AppCompatActivity implements View.OnClickListener {

    private static final String TAG = "QQLogin";
    private EditText mAccount;
    private EditText mPassword;
    private Button mBtnLogin;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_qqlogin);
        initView();
        initListener();
    }

    private void initListener() {
        mBtnLogin.setOnClickListener(this);
    }

    private void initView() {
        mAccount = findViewById(R.id.et_account);
        mPassword = findViewById(R.id.et_password);
        mBtnLogin = findViewById(R.id.btn_login);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.btn_login:
                Log.d(TAG, "点击了登录按钮");
                handlerLoginEvent(view);
        }
    }

    private void handlerLoginEvent(View view) {
        //拿到界面的内容，包括账号和密码
        //账号
        String accountText = mAccount.getText().toString();
        //密码
        String passwordText = mPassword.getText().toString();

        //把账号和密码保存起来
        //以一个文件的方式来保存
        saveUserInfo(accountText, passwordText);
    }


    private void saveUserInfo(String accountText, String passwordText) {
        Log.d(TAG, "保存用户信息");
        File file = new File("C:\\Users\\prnck\\AndroidStudioProjects\\Demo\\info.text");
        try {
        if (!file.exists()) {
            file.createNewFile();
        }
            FileOutputStream fos = new FileOutputStream(file);
            //以特定的方式去存储
            //存储形式：账号****密码
            fos.write((accountText + "****" + passwordText).getBytes());

            fos.close();
        } catch (Exception e) {
            e.printStackTrace();
        }


    }
}

报错：

2022-01-17 10:32:19.498 5275-5275/com.example.demo I/om.example.dem: Late-enabling -Xcheck:jni

2022-01-17 10:32:19.512 5275-5275/com.example.demo E/om.example.dem: Unknown bits set in runtime_flags: 0x8000

2022-01-17 10:32:20.085 5275-5275/com.example.demo I/Perf: Connecting to perf service.

2022-01-17 10:32:20.099 5275-5275/com.example.demo I/FeatureParser: can't find apollo.xml in assets/device_features/,it may be in /vendor/etc/device_features

2022-01-17 10:32:20.106 5275-5275/com.example.demo E/libc: Access denied finding property "ro.vendor.df.effect.conflict"

2022-01-17 10:32:20.106 5275-5275/com.example.demo E/libc: Access denied finding property "ro.vendor.knock.type"

2022-01-17 10:32:20.144 5275-5275/com.example.demo D/ForceDarkHelper: updateByCheckExcludeList: pkg: com.example.demo activity: com.example.demo.MainActivity@19851fb

2022-01-17 10:32:20.146 5275-5275/com.example.demo D/ForceDarkHelper: updateByCheckExcludeList: pkg: com.example.demo activity: com.example.demo.MainActivity@19851fb

2022-01-17 10:32:20.149 5275-5342/com.example.demo I/om.example.dem: The ClassLoaderContext is a special shared library.

2022-01-17 10:32:20.155 5275-5342/com.example.demo I/om.example.dem: The ClassLoaderContext is a special shared library.

2022-01-17 10:32:20.166 5275-5275/com.example.demo W/om.example.dem: Accessing hidden method Landroid/view/View;->computeFitSystemWindows(Landroid/graphics/Rect;Landroid/graphics/Rect;)Z (greylist, reflection, allowed)

2022-01-17 10:32:20.166 5275-5275/com.example.demo W/om.example.dem: Accessing hidden method Landroid/view/ViewGroup;->makeOptionalFitsSystemWindows()V (greylist, reflection, allowed)

2022-01-17 10:32:20.169 5275-5342/com.example.demo W/om.example.dem: Accessing hidden method Lmiui/contentcatcher/sdk/Token;-><init>(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;I)V (greylist, linking, allowed)

2022-01-17 10:32:20.170 5275-5342/com.example.demo W/om.example.dem: Accessing hidden method Lmiui/contentcatcher/InterceptorProxy;->getWorkThread()Landroid/os/HandlerThread; (greylist, linking, allowed)

2022-01-17 10:32:20.170 5275-5342/com.example.demo D/ViewContentFactory: initViewContentFetcherClass

2022-01-17 10:32:20.170 5275-5342/com.example.demo D/ViewContentFactory: getInterceptorPackageInfo

2022-01-17 10:32:20.170 5275-5342/com.example.demo W/om.example.dem: Accessing hidden method Landroid/app/AppGlobals;->getInitialApplication()Landroid/app/Application; (greylist, linking, allowed)

2022-01-17 10:32:20.170 5275-5342/com.example.demo D/ViewContentFactory: getInitialApplication took 0ms

2022-01-17 10:32:20.170 5275-5342/com.example.demo D/ViewContentFactory: packageInfo.packageName: com.miui.catcherpatch

2022-01-17 10:32:20.172 5275-5275/com.example.demo D/ForceDarkHelper: updateByCheckExcludeList: pkg: com.example.demo activity: com.example.demo.MainActivity@19851fb

2022-01-17 10:32:20.172 5275-5275/com.example.demo I/chatty: uid=10288(com.example.demo) identical 1 line

2022-01-17 10:32:20.176 5275-5275/com.example.demo D/ForceDarkHelper: updateByCheckExcludeList: pkg: com.example.demo activity: com.example.demo.MainActivity@19851fb

2022-01-17 10:32:20.180 5275-5342/com.example.demo D/ViewContentFactory: initViewContentFetcherClass took 10ms

2022-01-17 10:32:20.180 5275-5342/com.example.demo I/ContentCatcher: ViewContentFetcher : ViewContentFetcher

2022-01-17 10:32:20.180 5275-5342/com.example.demo D/ViewContentFactory: createInterceptor took 11ms

2022-01-17 10:32:20.181 5275-5342/com.example.demo W/om.example.dem: Accessing hidden method Lmiui/contentcatcher/sdk/ContentCatcherManager;->getInstance()Lmiui/contentcatcher/sdk/ContentCatcherManager; (greylist, linking, allowed)

2022-01-17 10:32:20.181 5275-5342/com.example.demo W/om.example.dem: Accessing hidden method Lmiui/contentcatcher/sdk/ContentCatcherManager;->registerContentInjector(Lmiui/contentcatcher/sdk/Token;Lmiui/contentcatcher/sdk/injector/IContentDecorateCallback;)V (greylist, linking, allowed)

2022-01-17 10:32:20.182 5275-5342/com.example.demo W/om.example.dem: Accessing hidden method Lmiui/contentcatcher/sdk/ContentCatcherManager;->getPageConfig(Lmiui/contentcatcher/sdk/Token;)Lmiui/contentcatcher/sdk/data/PageConfig; (greylist, linking, allowed)

2022-01-17 10:32:20.182 5275-5342/com.example.demo W/om.example.dem: Accessing hidden method Lmiui/contentcatcher/sdk/data/PageConfig;->getFeatures()Ljava/util/ArrayList; (greylist, linking, allowed)

2022-01-17 10:32:20.182 5275-5342/com.example.demo W/om.example.dem: Accessing hidden method Lmiui/contentcatcher/sdk/data/PageConfig;->getCatchers()Ljava/util/ArrayList; (greylist, linking, allowed)

2022-01-17 10:32:20.198 5275-5275/com.example.demo W/ActivityThread: SCHED: com.example.demo/.MainActivity [69, r=9ms, a=4ms, w=15ms]

2022-01-17 10:32:20.221 5275-5337/com.example.demo I/AdrenoGLES-0: QUALCOMM build          : a676c8e, I49c2a65814

  Build Date            : 10/15/20

  OpenGL ES Shader Compiler Version: EV031.29.00.15

  Local Branch           : 

  Remote Branch          : refs/tags/AU_LINUX_ANDROID_LA.UM.8.12.R1.10.00.00.561.106

  Remote Branch          : NONE

  Reconstruct Branch        : NOTHING

2022-01-17 10:32:20.221 5275-5337/com.example.demo I/AdrenoGLES-0: Build Config           : S P 8.0.12 AArch64

2022-01-17 10:32:20.221 5275-5337/com.example.demo I/AdrenoGLES-0: Driver Path           : /vendor/lib64/egl/libGLESv2_adreno.so

2022-01-17 10:32:20.226 5275-5337/com.example.demo I/AdrenoGLES-0: PFP: 0x016dd087, ME: 0x00000000

2022-01-17 10:32:20.357 5275-5275/com.example.demo W/ActivityThread: SCHED: com.example.demo/.MainActivity [52, r=34ms, a=31ms, w=154ms]

2022-01-17 10:32:22.347 5275-5275/com.example.demo I/Timeline: Timeline: Activity_launch_request time:6768023

2022-01-17 10:32:22.358 5275-5275/com.example.demo W/ActivityThread: SCHED: com.example.demo/.MainActivity [74, r=20ms, a=7ms, w=603ms]

2022-01-17 10:32:22.365 5275-5275/com.example.demo W/ActivityThread: handleWindowVisibility: no activity for token android.os.BinderProxy@5e91926

2022-01-17 10:32:22.370 5275-5342/com.example.demo D/ViewContentFactory: initViewContentFetcherClass

2022-01-17 10:32:22.370 5275-5342/com.example.demo I/ContentCatcher: ViewContentFetcher : ViewContentFetcher

2022-01-17 10:32:22.370 5275-5342/com.example.demo D/ViewContentFactory: createInterceptor took 0ms

2022-01-17 10:32:22.371 5275-5275/com.example.demo D/ForceDarkHelper: updateByCheckExcludeList: pkg: com.example.demo activity: com.example.demo.QQLogin@93da1b2

2022-01-17 10:32:22.399 5275-5275/com.example.demo I/chatty: uid=10288(com.example.demo) identical 8 lines

2022-01-17 10:32:22.400 5275-5275/com.example.demo D/ForceDarkHelper: updateByCheckExcludeList: pkg: com.example.demo activity: com.example.demo.QQLogin@93da1b2

2022-01-17 10:32:24.566 5275-5275/com.example.demo D/QQLogin: 点击了登录按钮

2022-01-17 10:32:24.567 5275-5275/com.example.demo D/QQLogin: 保存用户信息

2022-01-17 10:32:24.567 5275-5275/com.example.demo W/System.err: java.io.IOException: Read-only file system

2022-01-17 10:32:24.568 5275-5275/com.example.demo W/System.err:   at java.io.UnixFileSystem.createFileExclusively0(Native Method)

2022-01-17 10:32:24.568 5275-5275/com.example.demo W/System.err:   at java.io.UnixFileSystem.createFileExclusively(UnixFileSystem.java:317)

2022-01-17 10:32:24.568 5275-5275/com.example.demo W/System.err:   at java.io.File.createNewFile(File.java:1008)

2022-01-17 10:32:24.568 5275-5275/com.example.demo W/System.err:   at com.example.demo.QQLogin.saveUserInfo(QQLogin.java:66)

2022-01-17 10:32:24.568 5275-5275/com.example.demo W/System.err:   at com.example.demo.QQLogin.handlerLoginEvent(QQLogin.java:57)

2022-01-17 10:32:24.568 5275-5275/com.example.demo W/System.err:   at com.example.demo.QQLogin.onClick(QQLogin.java:44)

2022-01-17 10:32:24.568 5275-5275/com.example.demo W/System.err:   at android.view.View.performClick(View.java:7300)

2022-01-17 10:32:24.568 5275-5275/com.example.demo W/System.err:   at android.view.View.performClickInternal(View.java:7277)

2022-01-17 10:32:24.568 5275-5275/com.example.demo W/System.err:   at android.view.View.access$3600(View.java:822)

2022-01-17 10:32:24.568 5275-5275/com.example.demo W/System.err:   at android.view.View$PerformClick.run(View.java:28027)

2022-01-17 10:32:24.568 5275-5275/com.example.demo W/System.err:   at android.os.Handler.handleCallback(Handler.java:914)

2022-01-17 10:32:24.568 5275-5275/com.example.demo W/System.err:   at android.os.Handler.dispatchMessage(Handler.java:100)

2022-01-17 10:32:24.569 5275-5275/com.example.demo W/System.err:   at android.os.Looper.loop(Looper.java:239)

2022-01-17 10:32:24.569 5275-5275/com.example.demo W/System.err:   at android.app.ActivityThread.main(ActivityThread.java:7604)

2022-01-17 10:32:24.569 5275-5275/com.example.demo W/System.err:   at java.lang.reflect.Method.invoke(Native Method)

2022-01-17 10:32:24.569 5275-5275/com.example.demo W/System.err:   at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)

2022-01-17 10:32:24.569 5275-5275/com.example.demo W/System.err:   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:953)

2022-01-17 10:35:01.169 5275-5275/com.example.demo W/ActivityThread: SCHED: com.example.demo/.QQLogin [93, r=116ms, a=8ms, w=158767ms]

2022-01-17 10:35:01.822 5275-5342/com.example.demo W/om.example.dem: Accessing hidden method Lmiui/contentcatcher/sdk/ContentCatcherManager;->unregisterContentInjector(Lmiui/contentcatcher/sdk/Token;)V (greylist, linking, allowed)

adb：

C:\Users\prnck\AndroidStudioProjects\Demo>adb remount

Not running as root. Try "adb root" first.

remount failed

C:\Users\prnck\AndroidStudioProjects\Demo>adb root

adbd cannot run as root in production builds

把代码放出来，不知道你在干嘛

你的路径是啥呢？