straight 혹은 strange

[출처] StackOverflow - Android Studio E/dalvikvm﹕ Could not find class '.DatabaseHelper', referenced from method .DatabaseManager
                                  (http://stackoverflow.com/questions/32697460/android-studio-e-dalvikvm-could-not-find-class-databasehelper-referenced-fr) 

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <ImageButton
        android:id="@+id/exampleimg"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:gravity="center"
        android:padding="20dp"
        android:src="@mipmap/ic_launcher"/>
</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="50dp">

    <TextView
        android:id="@+id/popupquestion"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="left"
        android:padding="5dp"
        android:layout_margin="10dp"
        android:text="App.을 종료하겠습니까?"/>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:gravity="right"
        android:layout_below="@id/popupquestion">
    <Button
        android:id="@+id/yesbtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="5dp"
        android:padding="10dp"
        android:text="예"
        android:backgroundTint="@android:color/transparent" />

    <Button
        android:id="@+id/nobtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="5dp"
        android:layout_toRightOf="@id/yesbtn"
        android:text="아니오"
        android:backgroundTint="@android:color/transparent"/>
    </LinearLayout>
</RelativeLayout>

public class MainActivity extends AppCompatActivity {

    public ImageButton exampleImg;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // ImageButton 생성 및 연결. OnClickListener()로 Click시 PopupWindow를 생성하도록 함.
        exampleImg = (ImageButton)findViewById(R.id.exampleimg);
        exampleImg.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                final PopupWindow popupWindow = new PopupWindow(v); // onClick(View v)로 받아온 View 위에 PopupWindow 생성
                // PopupWindow에 반영할 layout을 다음과 같이 생성 및 연결
                LayoutInflater layoutInflater = (LayoutInflater) getBaseContext().getSystemService(LAYOUT_INFLATER_SERVICE);
                View popup = layoutInflater.inflate(R.layout.layout_popup, null);
                popupWindow.setContentView(popup);
                popupWindow.setWindowLayoutMode(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
                popupWindow.setTouchable(true); // PopupWindow 위에서 Button의 Click이 가능하도록 setTouchable(true);
                Button yesBtn = (Button) popup.findViewById(R.id.yesbtn); // PopupWindow 상의 View의 Button 연결
                Button noBtn = (Button) popup.findViewById(R.id.nobtn);
                yesBtn.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        finish(); // App.의 종료
                    }
                });
                noBtn.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        popupWindow.dismiss(); // PopupWindow의 해제
                    }
                });
                popupWindow.showAsDropDown(v); // PopupWindow를 View 위에 뿌려 줌. 선언하지 않을 경우, PopupWindow가 보이지 않음
            }
        });
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <TextView
        android:id="@+id/imgpath"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"/>

    <ImageView
        android:id="@+id/resultview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="center_horizontal"
        android:layout_below="@id/imgpath" />
</LinearLayout> 

    @Override
   protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (resultCode == RESULT_OK) // intent 결과 정상적으로 마쳐질 경우
        {
            /* 앞서 수행한 intent request 값이 image capture와 관련된 것일 경우 다음을 수행한다. */
            if (requestCode == CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE) 
            {
                ImageView resultView = (ImageView)findViewById(R.id.resultview); // .xml 에서 선언한 ImageView 변수를 Activity에도 선언한 후
                File tempImg = new File(fileUri.getPath()); // 앞서 지정한 경로에 파일의 경로에
                if(!tempImg.exists()){ // file이 존재하지 않으면
                    Log.d(TAG, "The image doesn't exist : " + tempImg.toString());
                    try {
                        FileOutputStream fos = new FileOutputStream(new File(fileUri.getPath())); // FileOutputStream 변수를 선언한 후
                        try {
                            fos.write(data.getExtras().getByte("data")); // Intent의 data 값을 write 하여 저장
                            fos.close(); // 그러고 나서 FileOutputStream을 종료한다.
                        } catch(IOException e){
                            Log.d(TAG, "IOException occur : " + e.getMessage());
                        }
                    } catch (FileNotFoundException e){
                        Log.d(TAG , "The image doesn't exist : "+ tempImg.toString());
                    }
                }
                Bitmap bm = BitmapFactory.decodeFile(fileUri.getPath()); // 해당 file을 Bitmap으로 decode 하여 저장한 후
                resultView.setImageBitmap(bm); // setImageBitmap() method로 앞서 선언한 ImageView에 촬영한 사진을 입력
                resultView.setRotation(imageViewRotation); // ImageView의 회전
            }
        }
    }