method bundle.putString not found an error

import android.content.Intent;
import android.view.View;

public class MainActivity extends Activity {

  public TextView mTextView;
  public static final String KEY_USERENTRY = "user_entry";

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

    mTextView = (TextView) findViewById(R.id.textView);
  }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
                outState.putString(KEY_USERENTRY,10);
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);

    }
}