在Android studio中创建和编写txt文件（Java代码）

Question

我正在尝试创建文件并在其上写入arrray的值，我的代码中没有错误，很可能有一些我无法看到的异常。

这是我的代码：

        for (int i = 0; i < groups.size(); i++) {
        try{
           Log.d("a" , "broj grupa " + groups.size());
           h = "C" + (i+1) + ".txt" ;
           // File root = new File(Environment.getExternalStorageDirectory(), "Notes");
           File root = new File(Environment.DIRECTORY_DOWNLOADS +h);
            if (!root.exists()) {
                root.mkdirs(); // this will create folder.
               // root.createNewFile();
            }
            File filepath = new File(root, h );
            FileWriter writer = new FileWriter(filepath);


            for(int ii=0 ; ii < groups.get(i).size(); ii++)
            {
                //  System.out.println(groups.get(i).get(ii)+"\n");
                String broj = groups.get(i).get(ii).toString();
                Log.d("ima li podataka ovamo ", broj);
                writer.write(broj);
                writer.flush();



            }

            writer.close();


        }
        catch(IOException e){
         e.toString();
        }
    }

主要活动：

                public class MainActivity extends Activity {


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    long [] array = new long[142];

    int kkkod;
    try {

        // OPENING THE REQUIRED TEXT FILE
        BufferedReader reader = new BufferedReader(new InputStreamReader(
           getAssets().open("renkhex.txt")));

        String myLine = reader.readLine();
         int i = 0;

        while (myLine != null) {

            String heksakodbezpraznina = myLine.replaceAll(" ", "");
            //Log.d("a da li je  to : " ,  heksakodbezpraznina);
             kkkod = Integer.parseInt(heksakodbezpraznina, 16);
           // Log.d("to je" , "integer vrednost = " + kkkod);
            array[i]= kkkod;
            i=i+1;
            myLine = reader.readLine();


          }

      reader.close();

    }
    catch (IOException e) {
             Toast.makeText(getApplicationContext(),
                "Error Opening the File !!!", Toast.LENGTH_LONG).show();
    }

    new  KMeans(3,142,array) ;


}

}

这是我的LogCat：

         Process: hesh.rtxt, PID: 2119
java.lang.RuntimeException: Unable to start activity ComponentInfo{hesh.rtxt/hesh.rtxt.MainActivity}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
        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:5001)
        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:785)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.NullPointerException
        at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:109)
        at hesh.rtxt.KMeans.<init>(KMeans.java:98)
        at hesh.rtxt.MainActivity.onCreate(MainActivity.java:59)
        at android.app.Activity.performCreate(Activity.java:5231)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)

当我运行程序时它不会停止，它也会写入很多输出来处理。