Question: I know running `javac file1.java` produces `file1.class` if `file1.java` is the only source file, then I can just say `java file1` to run it.

However, if I have 2 source files, `file1.java` and `file2.java`, then how do I build the program?

Answer: 
Try the following:

```
javac file1.java file2.java

```
OR you could just use `javac file1.java` and then also use `javac file2.java` afterwards.