New to Java. Getting an error in using parent abstract class.

I have an abstract class in one file. I am writing a subclass in another file.

FILE1:
package java.classes.mycode;
public abstract class Auto {....}

FILE2:
package java.classes.mycode;
class truck extends Auto {...}

When I try to compile my program, I get an error like:

Superclass java.classes.mycode.Auto of class java.classes.mycode.truck not found.
class truck extends Auto {
                            ^

What am I doing wrong?

Thanks in advance.
Theta.