Create a File object in memory from a string in Java

I have a function that accepts File as an argument. I don't want to create/write a new File (I don't have write access to filesystem) in order to pass my string data to the function. I should add that the String data don't exist in a file (so I cannot read my data from a file).

Can I use Streams and "cast" them to File objects?

Usually when a method accepts a file, there's another method nearby that accepts a stream. If this isn't the case, the API is badly coded. Otherwise, you can use temporary files, where permission is usually granted in many cases. If it's applet, you can request write permission.

An example:

try {
    // Create temp file.
    File temp = File.createTempFile("pattern", ".suffix");

    // Delete temp file when program exits.
    temp.deleteOnExit();

    // Write to temp file
    BufferedWriter out = new BufferedWriter(new FileWriter(temp));
    out.write("aString");
    out.close();
} catch (IOException e) {
}

No; instances of class File represent a path in a filesystem. Therefore, you can use that function only with a file. But perhaps there is an overload that takes an InputStream instead?

A File object in Java is a representation of a path to a directory or file, not the file itself. You don't need to have write access to the filesystem to create a File object, you only need it if you intend to actually write to the file (using a FileOutputStream for example)