I am trying to remove objects from my relative layout and replace the background with another image but I get a java.lang.NullPointerException on this line:

RelativeLayout ths = (RelativeLayout)findViewById(R.layout.activity_main);

Below is my code:

package com.ssrij.qrmag;

import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.TranslateAnimation;
import android.view.animation.Animation.AnimationListener;
import android.widget.Button;
import android.widget.RelativeLayout;
import android.widget.TextView;

public class MainActivity extends Activity {

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

            // Initialize animations
            Animation a = new TranslateAnimation(1000,0,0,0);
            Animation a1 = new TranslateAnimation(1000,0,0,0);
            Animation a2 = new TranslateAnimation(1000,0,0,0);
            Animation a3 = new TranslateAnimation(1000,0,0,0);

            // Set animation durations (ms)
            a.setDuration(1200);
            a1.setDuration(1400);
            a2.setDuration(1600);
            a3.setDuration(1800);

            // Get a reference to the objects we want to apply the animation to
            final TextView v = (TextView)findViewById(R.id.textView1);
            final TextView v1 = (TextView)findViewById(R.id.textView2);
            final TextView v2 = (TextView)findViewById(R.id.TextView3);
            final Button v3 = (Button)findViewById(R.id.tap_scan);

            // Clear existing animations, just in case...
            v.clearAnimation();
            v1.clearAnimation();
            v2.clearAnimation();
            v3.clearAnimation();

            // Start animating
            v.startAnimation(a);
            v1.startAnimation(a1);
            v2.startAnimation(a2);
            v3.startAnimation(a3);


            a1.setAnimationListener(new AnimationListener() {    
                @Override
                public void onAnimationStart(Animation animation) {  
                    // TODO Auto-generated method stub

                }

                @Override
                public void onAnimationRepeat(Animation animation) {
                    // TODO Auto-generated method stub

                }

                @Override
                public void onAnimationEnd(Animation animation) {

                v.setVisibility(View.INVISIBLE);
                v1.setVisibility(View.INVISIBLE);
                v2.setVisibility(View.INVISIBLE);
                v3.setVisibility(View.INVISIBLE);

                RelativeLayout ths = (RelativeLayout)findViewById(R.layout.activity_main);
                ths.setBackgroundResource(R.drawable.blurbg);

                }
            });


        }

        public void ScanQr(View v) {
            // Open the QR Scan page
            Intent a = new Intent(MainActivity.this, ScanActivity.class);
            startActivity(a);
        }

    }

Is there anything that I am doing wrong?