You need to create a new file with a file URI like file:/tmp/a.txt, but had this error:

java.io.IOException: No such file or directory
 at java.io.UnixFileSystem.createFileExclusively(Native Method)
 at java.io.File.createNewFile(File.java:947)
 at FileTest.main(FileTest.java:7)

The directory /tmp (or java.io.tmpdir) should already exist and should have write permission for the application. So the error message may be complaining the file (a.txt) does not exist. But a.txt is the new file you are trying to create and of course it doesn't exist. Take another look at the source code:

import java.io.File;
import java.net.URI;

public class FileTest {
    public static void main(String args[]) throws Exception {
        File f = new File(args[0]);
        boolean b = f.createNewFile();
        if(b) {
            System.out.printf("Successfully created new file: %s%n", f);
        } else {
            System.out.printf("Failed to create new file: %s%n", f);
        }
    }
}

Run this class with different input, such as /tmp/a.txt, file:/tmp/a.txt:

$ java FileTest /tmp/a
Successfully created new file: /tmp/a

$ java FileTest /tmp/a
Failed to create new file: /tmp/a
# This failure is expected since /tmp/a already exists.

$ java FileTest file:/tmp/a
Exception in thread "main" java.io.IOException: No such file or directory

So the cause of the IOException is input file URI is not a valid file path. If you have a file URI, then you should use another File constructor to instantiate the File:

//to instantiate a file with URI
//TODO: need to handle java.net.URISyntaxException 
File f = new File(new URI(args[0]));

//to instantiate a filw with path string
File f = new File(args[0]);