The code shows no error but the application is crashed

Question

The app crashes automatically here but shows no error

public class MainActivity extends AppCompatActivity {
 Button b1, b2;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 b1.findViewById(R.id.btn1);
 b2.findViewById(R.id.btn2);
 b1.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View v) {
 Toast toast1 = Toast.makeText(getApplicationContext(), "I am short", Toast.LENGTH_SHORT);
 toast1.show();
 Intent intent1 = new Intent(Intent.ACTION_VIEW);
 intent1.setData(Uri.parse("http://www.facebook.com"));
 startActivity(intent1);
 }
 });
 b2.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View v) {
 Open();
 Toast toast2 = Toast.makeText(getApplicationContext(), "I am here why to fear", Toast.LENGTH_LONG);
 toast2.show();
 }
 });
 }
 public void Open() {
 Intent intent2 = new Intent(this, Main2.class);
 startActivity(intent2);
 }
}

italic I can't find the error on this code but the application file is not opening. it says the application has stopped

Answer 1

Change this Code

 b1.findViewById(R.id.btn1);
 b2.findViewById(R.id.btn2)

With

 b1 = findViewById(R.id.btn1);
 b2 = findViewById(R.id.btn2);

Answer 2

Change this Code

b1.findViewById(R.id.btn1);
b2.findViewById(R.id.btn2);

With

b1 = (Button)findViewById(R.id.btn1);
b2 = (Button)findViewById(R.id.btn2);