Android Build a Simple Android App Basic Android Programming Generating a Random Number

my app stops.

when ever i tries to run my app it says your app stop working.i dont know whats happening.

this is my coding

package com.example.abhilakshaydhiman.funfacts;

import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.TextView;

public class FunFactsActivity extends AppCompatActivity { private TextView mFactTextView; private Button mShowFactButton;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_fun_facts);
    mFactTextView= (TextView) findViewById(R.id.factTextView);
    mShowFactButton= (Button) findViewById(R.id.showFactButton);
    View.OnClickListener listener=new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String fact="Ostriches can run faster than horses.";
            mFactTextView.setText(fact);
        }
    };
    mShowFactButton.setOnClickListener(listener);

}

}

HELP ME OUT.