Generation of random Image by tapping on imageView

I simply wants to generate a random image from drawable images when i tap on the imageView.Whenever i run this code, app on the emulator gets crashed. whats wrong with this code.

package com.example.surya.musicpleer;

import android.app.Activity;
import android.graphics.Typeface;
import android.support.v4.widget.TextViewCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;

import java.util.Random;

public class MainActivity extends Activity {

ImageView i1;
Random r = new Random();
int target = r.nextInt(3);
String drawablename = "photo" + target;

int resID = getResources().getIdentifier(drawablename, "drawable",  getPackageName());

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    i1 =(ImageView)findViewById(R.id.imageView);
    i1.setOnClickListener(new View.OnClickListener(){

        @Override
        public void onClick(View v) {
            i1.setImageResource(resID);
        }
    });
        }

}