My emulator isn't loading my app. It would say something like "Unfortunately, (name of app) has stopped working"

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity
        android:name=".FunFactsApp"
        android:label="@string/app_name"
        android:theme="@style/Theme.AppCompat">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_fun_facts_app);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();

            // 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 v) {
                    // 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);
        }
    });
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_fun_facts_app, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}