Something

JpegFile.java:

import java.io.*; 

public class JpegFile extends File {
	public JpegFile(String pathname) {
		super(pathname);
	}
}

TestCase.java:

public class TestCase {
	
	public static void main(String[] args) {
		JpegFile myFile = new JpegFile("./");
		for (JpegFile j : myFile.listFiles())
			System.out.println(j);
	}
	
}

--output:
javac TestCase.java
TestCase.java:5: inconvertible types
found   : java.io.File[]
required: JpegFile
                for (JpegFile j : ((JpegFile) myFile.listFiles()))
                                                              ^
1 error