Android : How to display random images on screen android

I have 7 images in the drawable folder. I would like to display them randomly on the screen. I am new to working with graphics. Right now it shows just one image on the screen.How can I display random images on the screen? Thanks

public class MyGraphics extends SurfaceView implements Runnable {

SurfaceHolder ourHolder;
Thread ourThread = null;
Boolean isRunning = true;
int[] images = new int[]{R.drawable.img1, R.drawable.img2, R.drawable.img3, R.drawable.img4, R.drawable.img5, R.drawable.img6,R.drawable.img7};


public void run() {



    while(isRunning){

        if(!ourHolder.getSurface().isValid())
         continue;

        Canvas ourCanvas = ourHolder.lockCanvas();
        ourCanvas.drawRGB(0, 0, 0);

        Bitmap img_blue = BitmapFactory.decodeResource(getResources(), R.drawable.mg1);
        ourCanvas.drawBitmap(img_blue, 0, 0, null);

        ourHolder.unlockCanvasAndPost(ourCanvas);




    }



}