What does the "...is not abstract..." error mean?

package com.manojabraham.funfacts;

import android.app.Activity;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;


public class FunFactsActivity extends Activity {

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

        // Declare our View variables and assign them the Views from the layout file.
        final TextView factLabel = (TextView) findViewById(R.id.factTextView);
        Button showFactButton = (Button) findViewById(R.id.showFactButton);
        View.OnClickListener listener = new View.OnClickListener() {
            @Override
            public void OnClick(View view) {
                // The button was clicked, so update the fact label with a new fact.
                String fact = "Ostriches can run faster than horses.";
                factLabel.setText(fact);
            }
        };
        showFactButton.setOnClickListener(listener);
    }