java获取文件的父目录

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

// 获取相对路径
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);