獲取首選項的子節點

Preferences 物件總是代表整個 Preferences 樹中的特定節點，有點像這樣：

/userRoot
├── com
│   └── mycompany
│       └── myapp
│           ├── darkApplicationMode=true
│           ├── showExitConfirmation=false
│           └── windowMaximized=true
└── org
    └── myorganization
        └── anotherapp
            ├── defaultFont=Helvetica
            ├── defaultSavePath=/home/matt/Documents
            └── exporting
                ├── defaultFormat=pdf
                └── openInBrowserAfterExport=false

要選擇/com/mycompany/myapp 節點：

1. 按照慣例，基於類的包：

   package com.mycompany.myapp;
   
   // ...
   
   // Because this class is in the com.mycompany.myapp package, the node
   // /com/mycompany/myapp will be returned.
   Preferences myApp = Preferences.userNodeForPackage(getClass());
   

2. 按相對路徑：

   Preferences myApp = Preferences.userRoot().node("com/mycompany/myapp");
   

   使用相對路徑（不以/開頭的路徑）將導致路徑相對於其解析的父節點被解析。例如，以下示例將返回路徑/one/two/three/com/mycompany/myapp 的節點：

   Preferences prefix = Preferences.userRoot().node("one/two/three");
   Preferences myAppWithPrefix = prefix.node("com/mycompany/myapp");
   // prefix          is /one/two/three
   // myAppWithPrefix is /one/two/three/com/mycompany/myapp
   

3. 按絕對路徑：

   Preferences myApp = Preferences.userRoot().node("/com/mycompany/myapp");
   

   在根節點上使用絕對路徑與使用相對路徑沒有區別。不同之處在於，如果在子節點上呼叫，則將相對於根節點解析路徑。

   Preferences prefix = Preferences.userRoot().node("one/two/three");
   Preferences myAppWitoutPrefix = prefix.node("/com/mycompany/myapp");
   // prefix            is /one/two/three
   // myAppWitoutPrefix is /com/mycompany/myapp