NullableQuantity.java

package de.hftstuttgart.units;

import java.text.NumberFormat;
import java.text.ParseException;
import java.util.Locale;
import java.util.Optional;

import javax.measure.Quantity;
import javax.measure.Unit;

import tech.units.indriya.format.SimpleQuantityFormat;
import tech.units.indriya.quantity.Quantities;

/**
 * A <code>NullableQuantity</code> wraps a <code>javax.measure.Quantity</code> having
 * a numerical value that is either a <code>Double</code>, a <code>Long</code>,
 * or <code>null</code>. The latter case represents an unknown numerical
 * value of a specific unit. On the other hand, the <code>javax.measure.Unit</code>
 * of the quantity is always defined.
 */
public class NullableQuantity {

	static {
		// TODO Implement specific QuantityFormat to enable custom number format?
		// ensure that editing, (de)serialization and default values of units all work
		// with the same number format (Decimal point etc.)
		Locale.setDefault(Locale.ENGLISH);
		
		// specific additional units for urban simulation like TON (t), PARTS_PER_MILLION (ppm), DECIBEL (dB)
		UrbanSimulationUnits.getInstance();
	}

	public static NullableQuantity create(String str) {
		NullableQuantity newNullableQuantity = null;
		try {
			NumberFormat.getInstance().parse(str);
			newNullableQuantity = new NullableQuantity(str);
		} catch (final ParseException ex) { // no number value present: create NullQuantity just with unit
			try {
				NullableQuantity dummy = new NullableQuantity("1 " + str); //$NON-NLS-1$
				newNullableQuantity = new NullQuantity(dummy.getUnit());
			} catch (final IllegalArgumentException ex1) { // Unit could not be parsed
				System.out.println("Unit '" + str + "'  could not be parsed!"); //TODO
				ex.printStackTrace();
			}
		} catch (final IllegalArgumentException ex) { // Quantity could not be parsed
			System.out.println("Quantity '" + str + "' could not be parsed!");	//TODO
			ex.printStackTrace();
		}
		return newNullableQuantity;
	}

	public static NullableQuantity create(Number number, Unit<?> unit) {
		return number == null ? new NullQuantity(unit) : new NullableQuantity(number, unit);
	}

	private final Quantity<?> quantity;

	private NullableQuantity(String str) {
		quantity = Quantities.getQuantity(str);
	}

	private NullableQuantity(Number number, Unit<?> unit) {
		quantity = Quantities.getQuantity(number, unit);
	}

	/**
	 * In case of an unknown numerical value of the quantity an empty <code>Optional</code> is returned via subclass.
	 * @return the wrapped <code>javax.measure.Quantity</code> if its numerical value is present
	 */