Android 判断是否是第一次启动

public class PreferenceTestMain extends Activity {
public static final String PREFS_NAME = “MyPrefsFile”;
public static final String FIRST_RUN = “first”;
private boolean first;

/** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);
            // Restore preferences
            SharedPreferences settings =
            getSharedPreferences(PREFS_NAME, 0);
            first =settings.getBoolean(FIRST_RUN, true);

            if (first) {
               //是第一次启动  可执行相应操作
            } else {
               //不是第一次 启动
            }

    }

/**
*其中在 onCreate 方法中读取，SharedPreferences 信息，在 *onStop 中保存 SharedPreferences信息。注意程序的状态信息般都在 onStop 保存。
*/
@Override
protected void onStop() {
super.onStop();

    // We need an Editor object to make preference changes.
    // All objects are from android.context.Context
        SharedPreferences settings =
        getSharedPreferences(PREFS_NAME, 0);

            SharedPreferences.Editor editor = settings.edit();
            if (first) {
             editor.putBoolean(FIRST_RUN, false);
             /**Commit the edits!*/
             editor.commit();
             }else{  

             }
    }

}