I would have thought that something like this would be much better, since you're adding a variable, so why not restrict access and make it cleaner? Your getter/setters should do what they say on the tin.
public abstract class ExternalScript extends Script {
private String source;
public void setSource(String file) {
source = file;
}
public String getSource() {
return source;
}
}
Bringing this back to the question, do you ever bother looking at where the getter/setter code is when reading it? If they all do getting and setting then you don't need to worry about what the function 'does' when reading the code. There are a few other reasons to think about too:
Always think whether your class is really a different thing or not, and that should help decide whether you need anything more.