Java 6类加载的速度有多快？(What's faster in Java 6 classloading?)

 PreferenceActivity的文档说： 
 
 
 
 如果您在旧模式下使用PreferenceActivity，则[PreferenceFragment]文档将在此处应用于已弃用的API。 
 
 
 PreferenceFragment的文档解释了正在发生的事情： 
 
 
 
 要检索此片段中的首选项层次结构将使用的SharedPreferences实例，请使用与此片段相同的包中的上下文调用getDefaultSharedPreferences（android.content.Context）。 
 
 
 这表明PreferenceActivity#addPreferencesFromResource(...)不会创建与原始名称相同的SharedPreferences文件。 相反，它将文件合并到默认的共享首选项中。 pref_general文件不存在，当您尝试从中读取时，基本上就是创建它。 （虽然在编辑之前它实际上并不是在磁盘上创建的。） 

The docs for PreferenceActivity say:
 
 
 
If you are using PreferenceActivity in its old mode, the documentation [for PreferenceFragment] applies to the deprecated APIs here. 
 
 
And the docs for PreferenceFragment explain what's happening:
 
 
 
To retrieve an instance of SharedPreferences that the preference hierarchy in this fragment will use, call getDefaultSharedPreferences(android.content.Context) with a context in the same package as this fragment.
 
 
This suggests that PreferenceActivity#addPreferencesFromResource(...) does not create a SharedPreferences file with the same name as the original. Instead, it merges the file into the default shared preferences. The pref_general file does not exist, and you're basically creating it when you attempt to read from it. (Though it's not actually created on disk until you edit it.)