How to denote directory and file in File class?

Question

Why "w3/w3.txt" treated as directory in the File class? If i want to create a file in non existing directory I must create two separate File objects (for directory and file), and create directory explicitly via mkdir() or mkdirs()?

import java.io.*;

public class Test
{
    public static void main(String[] args) throws IOException
    {
        File f1 = new File("w1.txt"); // file
        File f2 = new File("w2/w2"); // directory
        File f3 = new File("w3/w3/"); // directory
        File f4 = new File("w4/w4.txt"); // directory (why treated as directory?)
    }
}