Admob ad not visible on Android Emulator

Delete - unistal app from testing device - emulator and try again RUN - DEBUGG your app.

Copy file to another

        File path = Environment.getExternalStoragePublicDirectory(
                Environment.DIRECTORY_PICTURES);
        File file = new File(path, "MyPicture.jpg");
           // the Pictures directory exists? 
            path.mkdirs();
            InputStream is = getResources().openRawResource(R.drawable.flower_blue);
            OutputStream os = new FileOutputStream(file);
            byte[] data = new byte[is.available()];
            is.read(data);
            os.write(data);
            is.close();
            os.close();

Copy and compress file

Bitmap bitmapOrg = BitmapFactory.decodeResource(getResources(),
					R.drawable.flower_blue);

try {
	 FileOutputStream out = new FileOutputStream("new_bitmap.jpg");
		bitmapOrg.compress(Bitmap.CompressFormat.JPEG, 90, out);
} catch (Exception e) {
	e.printStackTrace();
	Log.e("saveBitmap", e.getMessage());
} 

List LinkedList Collections add sort find search Item, get searched item to string in Java example.

MainClass.java

import java.util.Collections;
import java.util.LinkedList;
import java.util.List;

public class MainClass {
	public static void main(String[] arg) {
		String[] arrayOfString = {"nothing", "Hello", "people"
				, "bye-bye", "hello", "world!", "End" };
		   
                   List<String> arrayList = new LinkedList<String>();
                  
                   for(String s: arrayOfString)
		     arrayList.add(s);

		    Collections.sort(arrayList);
		    // foreach
		    for (String str: arrayList)
		      System.out.println(str);
		    
		    Object objMin = Collections.min(arrayList);
		    System.out.println("Min is: " + objMin);
		    
		    Object objMax = Collections.max(arrayList);
		    System.out.println("Max is: " + objMax);
		    
		    int index = Collections.binarySearch(arrayList, "people");
		    System.out.println("Index of people is: " + index);
		    // print word on index 5
		    System.out.println("Index 5 is: " + arrayList.get(5));
                    String sItem = arrayList.get(5); // get item from index 5 to string
		    
		  }
}
/*
End
Hello
bye-bye
hello
nothing
people
world!
Min is: End
Max is: world!
Index of people is: 5
Index 5 is: people
*/

If You have old PC (Android in emulator with high screen resolution uses a lot of memory) or your testing phone have small screen, You can try this trick.
Rename layout folder for small device screen f.g. from layout into layout-swXXXdp and a large layout-sw600dp into layout.
Your phone with small screnn will do select xml file from renamed layout folder (for small screen).
You can to testing rotation with device en stability of fragments if an application changed orientation.
If you have old pc, you can try to make a new virtual device running on older version of Android, which uses less memory of computer.
For testing of rotation stability - application orientation changed - use on emulator Ctrl+F11, Ctrl+F12 key (Windows).

Important
Before the release of application, you have to rename layout folder to older name layout-sw600dp and layout-swXXXdp to layout.

To hide a module File->Project Structure Ctrl+Alt+Shift+S
In left panel click on Module which want to hide.
Click on minus symbol (-) on upper left corner of window.
Click Yes.

To delete module from disk click on module in project tree (to select) and press Delete on keyboard.