api文档中的:
If parent is the empty string then the new File instance is created by converting child into an abstract pathname and resolving the result against a system-dependent default directory.
如果 parent是空字符串,child就被转换成抽象路径名(abstract pathname)来创建File的对象(instance)
看了半天,始终不理解这里用abstract这个概念是什么意思 或则起什么作用
其实后面还有一句:
Otherwise each pathname string is converted into an abstract pathname and the child abstract pathname is resolved against the parent.
分别把parent和child两个路径名转换为abstract pathname