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File file = new File("a.txt");
String parentPath = file.getParent(); // null
File parentDir = file.getParentFile(); // null
System.out.println("parentPath="+parentPath); 

// »ñÈ¡Ïà¶Ô·¾¶
file = new File("D:/zhxn\\a.txt");
parentPath = file.getParent(); // D:\zhxn
parentDir = file.getParentFile(); // D:\zhxn
System.out.println("parentPath="+parentPath);

parentPath = parentDir.getParent(); // D:\
parentDir = parentDir.getParentFile(); // D:\
System.out.println("parentPath="+parentPath);


parentPath = parentDir.getParent(); // null
parentDir = parentDir.getParentFile(); // null
System.out.println("parentPath="+parentPath);

תÔØÓÚ:https://www.cnblogs.com/zhxn/p/9243519.html