Clean Code

Args Implementation
you should understand what the 
ArgumentMarshaler
interface is and what its derivatives do.
I’ll show a few of them to you now (Listing 14-3 through Listing 14-6).
Listing 14-3 
ArgumentMarshaler.java
public interface ArgumentMarshaler {
void set(Iterator currentArgument) throws ArgsException;
}
Listing 14-4 
BooleanArgumentMarshaler.java
public class BooleanArgumentMarshaler implements ArgumentMarshaler {
private boolean booleanValue = false;
public void set(Iterator currentArgument) throws ArgsException {
booleanValue = true;
}
public static boolean getValue(ArgumentMarshaler am) {
if (am != null && am instanceof BooleanArgumentMarshaler)
return ((BooleanArgumentMarshaler) am).booleanValue;
else
return false;
}
}
Listing 14-5 
StringArgumentMarshaler.java
import static com.objectmentor.utilities.args.ArgsException.ErrorCode.*;
public class StringArgumentMarshaler implements ArgumentMarshaler {
private String stringValue = "";
public void set(Iterator currentArgument) throws ArgsException {
try {
stringValue = currentArgument.next();
} catch (NoSuchElementException e) {
throw new ArgsException(MISSING_STRING);
}
}
public static String getValue(ArgumentMarshaler am) {
if (am != null && am instanceof StringArgumentMarshaler)
return ((StringArgumentMarshaler) am).stringValue;
else
return "";
}
}

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198
Chapter 14: Successive Refinement
The other 
ArgumentMarshaler
derivatives simply replicate this pattern for 
doubles
and
String
arrays and would serve to clutter this chapter. I’ll leave them to you as an exercise.
One other bit of information might be troubling you: the definition of the error code
constants. They are in the 
ArgsException
class (Listing 14-7).