Java circular enum constructors (catch 22)

I have an enum for MeasurementTypes, that says a TEMPERATURE measurement uses units CELSIUS or FAHRENHEIT.

Then I have a Units class which defines CELSIUS and FAHRENHEIT as being TEMPERATURE measurements.

I create a measurement, get the measurement type, and discover in the constructor for MeasurementType the TEMPERATURE measurement type doesn't have the units CELSIUS and FAHRENHEIT filled in.

I suppose because TEMPERATURE needs CELSIUS and FAHRENHEIT to already exist and be initialized, while CELSIUS and FAHRENHEIT need TEMPERATURE to already exist and be initialized.

Well that's a fine mess of spaghetti I've gotten myself into now. Any suggestions how to get around this?

Below is some sample code:
public enum Units {
	
	CELSIUS(MeasurementType.TEMPERATURE),
	FAHRENHEIT(MeasurementType.TEMPERATURE);

	
	private final MeasurementType measurementType;

	//CONSTRUCTORS
	private Units(MeasurementType measurementType) {
		this.measurementType = measurementType;
	}
}

Open in new window

import java.util.ArrayList;
import java.util.List;
import java.util.Arrays;

public enum MeasurementType {
	TEMPERATURE(  new ArrayList<Units>(Arrays.asList( Units.CELSIUS, Units.FAHRENHEIT )) );
	
	private List<Units> unitsList;

	//CONSTRUCTORS
	private MeasurementType(List<Units> ul) {
		System.out.println("MeasurementType:CONSTRUCTOR: ul=" + ul);
		this.unitsList = ul;
	}
}

Open in new window

public class Measurement {

	private final double value;
	private final Units units;
	
	public Measurement(double value, Units units) {
		this.value = value;
		this.units = units;
	}
}

Open in new window

public class Test {

    public static void main(String[] args) {
	    Measurement measurement = new Measurement(13.1, Units.CELSIUS);
    }
}

Open in new window

Output:
MeasurementType:CONSTRUCTOR: ul=[null, null]

(was hoping for ul=[CELSIUS, FAHRENHEIT])
deleydAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

dpearsonCommented:
I think you're trying to store a list of units in two places at once.

First in the Units enum (since that's what an enum is - a list of things) and again in MeasurementType.

To me that's a poor design and at the root of why you're getting circular definitions.  I think you should just have one list - the enum in Units.

Something like this:

public enum Units {

	FEET(MeasurementType.LENGTH),
	CELSIUS(MeasurementType.TEMPERATURE),
	FAHRENHEIT(MeasurementType.TEMPERATURE);

	// You can move this to its own class/file if you prefer but it would only
        // have this one line - don't try to move the other methods as well.
	public enum MeasurementType { TEMPERATURE, LENGTH } ;

	private final MeasurementType measurementType;

	//CONSTRUCTORS
	private Units(MeasurementType measurementType) {
		this.measurementType = measurementType;
	}

	public List<Units> getTemperatureUnits() {
		return getUnitsByMeasurementType(MeasurementType.TEMPERATURE) ;
	}

	public List<Units> getLengthUnits() {
		return getUnitsByMeasurementType(MeasurementType.LENGTH) ;
	}

	private List<Units> getUnitsByMeasurementType(MeasurementType type) {
		List<Units> units = new ArrayList<>() ;

		for (Units unit : values()) {
			if (unit.measurementType == type)
				units.add(unit) ;
		}

		return units ;
	}
}

Open in new window


Any good?

Doug
0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
deleydAuthor Commented:
Yup that's pretty much what I figured after taking a break and eating some dinner.

I was trying to make it easy by having the info right there, and it ended up making it hard.
0
dpearsonCommented:
Dinner solves many a hard problem :)

Doug
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Java

From novice to tech pro — start learning today.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.