exist（）不起作用，但getAbsolutePath（）起作用

Question

I have the below code whereby I create a File type based on a pre-created file "test.brd" and also call the getAbsolutePath() method on this File, this all works correctly. However, when I run the exists() method, this is deemed as not existing.

When I debug, the status of the File is null and the path is also null, yet the getAbsolutePath() method works. I have debugged and it goes to the Security section of the exists() method.

Please see below:

File inputFile = new File("/Users/myname/Desktop/project_name/test.brd");
// The below works and returns the path
System.out.println(inputFile.getAbsolutePath());
if (inputFile.exists()) {
    System.out.println("Exists");
}
else {
    System.out.println("Invalid");
}

Even when I construct the file without the absolute path and just give the file name as a parameter (stored locally with Java file) the correct absolute path is provided.

Hope this makes sense. All I want to do is read a pre-created file into an Array, each character is an element in the array, I was intending on using scanner to read the file, but inputFile does not exist to be read.

Answer 1

The two methods are about different aspects of the file:

• getAbsolutePath() is about file name. In a way, this is a "string manipulation method" completely separated from the actual file system
• exists() is about the actual file. It checks whether or not the file is present in the file system at the location identified by the given path.

Note that getAbsolutePath() and other path manipulation methods of File must work even without the file or the folder being present in the actual file system. Otherwise, the API would not be able to support file creation, eg through createNewFile() .

Answer 2

If you take a look at the javadoc , you can find the following sentence

Instances of this class may or may not denote an actual file-system object such as a file or a directory.

Proving that the instance in memory of a File object is not necessarily a real file or directory existing in the file system.

Answer 3

File inputFile = new File("/Users/myname/Desktop/project_name/test.brd"); The line above doesn't create a new File and hence it doesn't exists. If you want to create a file you can use method inputFile.createNewFile() . The method getAbsolutePath() works on the inputFile object and is completely different from file creation.