e411. getting the roots of the preference trees.txt

这里面包含了一百多个JAVA源文件

There are two preference trees --- the system tree and the user tree. The root of these trees is retrieved using Preferences.systemRoot() and Preferences.userRoot(). The roots are required when creating and retrieving preference nodes. See e413 Retrieving a Preference Node for an example of retrieving preference nodes using a root. 
    // Get the system root
    Preferences prefs = Preferences.systemRoot();
    
    // Get the user root
    prefs = Preferences.userRoot();
    
    // The name of a root is ""
    String name = prefs.name();
    
    // The parent of a root is null
    Preferences parent = prefs.parent();
    
    // The absolute path of a root is "/"
    String path = prefs.absolutePath();