是否可以写入Android设备的内部存储，查看设备上是否已经安装了app？

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

String filename = "myfile.txt";
String content = "Hello, World!";

File file = new File(getFilesDir(), filename);

try {
    FileOutputStream fos = new FileOutputStream(file);
    fos.write(content.getBytes());
    fos.close();
} catch (IOException e) {
    e.printStackTrace();
}

String packageName = "com.example.myapp";

PackageManager pm = getPackageManager();
try {
    PackageInfo packageInfo = pm.getPackageInfo(packageName, 0);
    // 应用已安装
} catch (PackageManager.NameNotFoundException e) {
    // 应用未安装
    e.printStackTrace();
}