java.io.File的两种构造方法是否执行相同功能？针对mkdirs()调用场景的疑问

Great question! Let's break this down clearly, starting with what each constructor does and then focusing on your specific scenario.

First, let's outline the core behavior of each constructor:

• File(String parent, String child): This takes a parent directory path and a child path (file/directory name), then combines them using your system's default path separator (like / on Android/Unix systems, \ on Windows) to form the full path for the new File object.
• File(String pathname): This directly uses the complete path string you provide to create the File object, no拼接 needed.

For your exact example #

When you run:

new File("/storage/emulated/0", "directory").mkdirs()

The constructor will combine the parent path /storage/emulated/0 and child name directory into the full path /storage/emulated/0/directory (since Android uses / as the path separator). This is exactly the same as passing the full path directly to the other constructor:

new File("/storage/emulated/0/directory").mkdirs()

In this scenario, the two calls are 100% functionally identical: both will attempt to create the directory folder under /storage/emulated/0, and mkdirs() will handle creating any missing parent directories (though that's not necessary here since /storage/emulated/0 is typically Android's external storage root).

When might they behave differently? #

The only edge case where these constructors diverge is if the child parameter is an absolute path itself. For example:

new File("/storage/emulated/0", "/system/app").mkdirs()

Here, the constructor ignores the parent path entirely and uses the absolute child path /system/app instead. So this is equivalent to new File("/system/app").mkdirs(), not new File("/storage/emulated/0/system/app").mkdirs(). That's an important detail to keep in mind.

内容的提问来源于stack exchange，提问作者Viktor