问如何实现URL中的开关案例映像

EN

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;


public class MainActivity extends AppCompatActivity {



/**
 * ATTENTION: This was auto-generated to implement the App Indexing API.
 * See https://g.co/AppIndexing/AndroidStudio for more information.
 */
 //   private GoogleApiClient client;
    private ImageView iv;
    private int a;
    private Bitmap bitmap;
 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
 //   iv = (ImageView) findViewById(R.id.imageView1);

   // bitmap = getBitmapFromURL("http://icons.iconarchive.com/icons    /crountch/one-piece-jolly-roger/72/Luffys-flag-2-icon.png");
   //     iv.setImageBitmap(bitmap);
    // ATTENTION: This was auto-generated to implement the App Indexing API.
    // See https://g.co/AppIndexing/AndroidStudio for more information.
  //  client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
}


 public void buttonOnClick(View v)  {
    // do something when the button is clicked
    Button button = (Button) v;

    a = (byte) (Math.random() * 2);

    switch (a) {
        case 1:
            iv = (ImageView) findViewById(R.id.imageView1);

            bitmap = getBitmapFromURL("http://icons.iconarchive.com/icons/crountch/one-piece-jolly-roger/72/Luffys-flag-2-icon.png");
            iv.setImageBitmap(bitmap);
        break;
      //  iv.setImageBitmap(bitmap);
        case 2:

        break;
    }
}
public Bitmap getBitmapFromURL(String src) {
    try {
        URL url = new URL(src);
        HttpURLConnection connection = (HttpURLConnection) url
                .openConnection();
        connection.setDoInput(true);
        connection.connect();
        InputStream input = connection.getInputStream();
        Bitmap myBitmap = BitmapFactory.decodeStream(input);
        return myBitmap;

    } catch (Exception e) {
        // TODO: handle exception
        e.printStackTrace();
        return null;
    }

}

}

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Image text"
    android:id="@+id/textView"
    android:layout_below="@+id/textView2"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="82dp" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Image"
    android:id="@+id/button"
    android:onClick="buttonOnClick"
    android:layout_below="@+id/textView"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="41dp" />

<ImageView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/imageView1"
    android:layout_alignParentBottom="true"
    android:layout_alignRight="@+id/textView"
    android:layout_alignEnd="@+id/textView"
    android:layout_marginBottom="106dp" />

</RelativeLayout>