can you help me please?: error whtih inheritance

I tried to compile but i always have the same error. I have 2 class in the same package,one abc and the other is def ; Here you can see my class :
public class abc {
public abc(){}
}

public class def extends abc {
public static void main(String arg[]) {
System.out.println("compiled and executed");
}
}

I have this error:

def.java:1: cannot resolve symbol
symbol : class abc
location: class def
public class def extends abc {
^
1 error
Can you answer please.....thanks a lot!

Are both .java files in the same directory?
How are you compiling these files?
It could be that you don't have your classpath set up correctly.
How are you compiling both of the files?
you should probably be in the same directory as the two files when you type javac, then you can type
javac -classpath ./ def.java
and the compiler will be able to find the referenced abc.java file.

okucuen
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Rob , it's very nice from you?You're right. i had a problem whith my environnement variable. Classpath and path !!I changed it.
Dave , i thanks you so, As you can see , i have my name changed