File.mkdirs() creating a directory instead of a file

Question

I am trying to serialize the following class:

public class Library extends ArrayList<Book> implements Serializable{

public Library(){
    check();
}

using the following method of that class:

void save() throws IOException {
    String path = System.getProperty("user.home");
    File f = new File(path + "\\Documents\\CardCat\\library.ser");    

    ObjectOutputStream oos = new ObjectOutputStream (new FileOutputStream (f));  
    oos.writeObject(this);
    oos.close();
}

However, rather than creating a file called library.ser, the program is creating a directory named library.ser with nothing in it. Why is this?

If its helpful, the save() method is initially called from this method (of the same class):

void checkFile() {
    String path = System.getProperty("user.home");
    File f = new File(path + "\\Documents\\CardCat\\library.ser");    

    try {    
         if (f.exists()){
             load(f);
         }
         else if (!f.exists()){
             f.mkdirs();
             save();
         }
    } catch (IOException | ClassNotFoundException ex) {
         Logger.getLogger(Library.class.getName()).log(Level.SEVERE, null, ex);
    }
}

Answer 1

File.mkdirs() creating a directory instead of a file

That's what it's supposed to do. Read the Javadoc. Nothing there about creating a file.

f.mkdirs();

It is this line that creates the directory. It should be

f.getParentFile().mkdirs();