Zapis danych do pliku – aplikacja wywala się

package com.example.user.myapplication;

import java.io.FileNotFoundException;
import java.io.PrintWriter;

public class MainActivity{
    public static void main(String[] args) throws FileNotFoundException{
        PrintWriter zapis = new PrintWriter("ala.txt");
        zapis.println("Ala ma kota, a kot ma Alę");
        zapis.close();
    }
}

completed successfully	6s 131ms
Run build	5s 397ms
Load build	6ms
Configure build	1s 675ms
Calculate task graph	53ms
Run tasks	3s 568ms

05/28 19:35:06: Launching app
No apk changes detected since last installation, skipping installation of C:\Users\user\AndroidStudioProjects\MyApplication\app\build\outputs\apk\debug\app-debug.apk
$ adb shell am force-stop com.example.user.myapplication
$ adb shell am start -n "com.example.user.myapplication/com.example.user.myapplication.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER -D
Waiting for application to come online: com.example.user.myapplication.test | com.example.user.myapplication
Connecting to com.example.user.myapplication
Capturing and displaying logcat messages from application. This behavior can be disabled in the "Logcat output" section of the "Debugger" settings page.
I/System.out: Sending WAIT chunk
W/ActivityThread: Application com.example.user.myapplication is waiting for the debugger on port 8100...
I/dalvikvm: Debugger is active
I/System.out: Debugger has connected
              waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
Connected to the target VM, address: 'localhost:8647', transport: 'socket'
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: debugger has settled (1493)
D/AndroidRuntime: Shutting down VM
W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0x9cd45b20)
E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.user.myapplication, PID: 2525
                  java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.user.myapplication/com.example.user.myapplication.MainActivity}: java.lang.ClassCastException: com.example.user.myapplication.MainActivity cannot be cast to android.app.Activity
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
                      at android.app.ActivityThread.access$800(ActivityThread.java:135)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:136)
                      at android.app.ActivityThread.main(ActivityThread.java:5017)
                      at java.lang.reflect.Method.invokeNative(Native Method)
                      at java.lang.reflect.Method.invoke(Method.java:515)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
                      at dalvik.system.NativeStart.main(Native Method)
                   Caused by: java.lang.ClassCastException: com.example.user.myapplication.MainActivity cannot be cast to android.app.Activity
                      at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245) 
                      at android.app.ActivityThread.access$800(ActivityThread.java:135) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:136) 
                      at android.app.ActivityThread.main(ActivityThread.java:5017) 
                      at java.lang.reflect.Method.invokeNative(Native Method) 
                      at java.lang.reflect.Method.invoke(Method.java:515) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
                      at dalvik.system.NativeStart.main(Native Method) 
Disconnected from the target VM, address: 'localhost:8647', transport: 'socket'

05/28 19:52:49: Launching app
$ adb push C:\Users\user\AndroidStudioProjects\MyApplication\app\build\outputs\apk\debug\app-debug.apk /data/local/tmp/com.example.user.myapplication
$ adb shell pm install -t -r "/data/local/tmp/com.example.user.myapplication"
WARNING: linker: libdvm.so has text relocations. This is wasting memory and is a security risk. Please fix.
	pkg: /data/local/tmp/com.example.user.myapplication
Success


$ adb shell am start -n "com.example.user.myapplication/com.example.user.myapplication.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER
Client not ready yet..Waiting for process to come online
Connected to process 2161 on device emulator-5554