// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html
/*
 *******************************************************************************
 * Copyright (C) 2004-2016, Google Inc, International Business Machines
 * Corporation and others. All Rights Reserved.
 *******************************************************************************
 */
package com.ibm.icu.util;

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.io.ObjectStreamException;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import com.ibm.icu.impl.CollectionSet;
import com.ibm.icu.impl.ICUData;
import com.ibm.icu.impl.ICUResourceBundle;
import com.ibm.icu.impl.UResource;
import com.ibm.icu.impl.units.MeasureUnitImpl;
import com.ibm.icu.impl.units.SingleUnitImpl;
import com.ibm.icu.text.UnicodeSet;


/**
 * A unit such as length, mass, volume, currency, etc.  A unit is
 * coupled with a numeric amount to produce a Measure. MeasureUnit objects are immutable.
 * All subclasses must guarantee that. (However, subclassing is discouraged.)

 *
 * @see com.ibm.icu.util.Measure
 * @author Alan Liu
 * @stable ICU 3.0
 */
public class MeasureUnit implements Serializable {
    private static final long serialVersionUID = -1839973855554750484L;

    // Cache of MeasureUnits.
    // All access to the cache or cacheIsPopulated flag must be synchronized on class MeasureUnit,
    // i.e. from synchronized static methods. Beware of non-static methods.
    private static final Map<String, Map<String,MeasureUnit>> cache
        = new HashMap<>();
    private static boolean cacheIsPopulated = false;

    /**
     * If type set to null, measureUnitImpl is in use instead of type and subType.
     * @internal
     * @deprecated This API is ICU internal only.
     */
    @Deprecated
    protected final String type;

    /**
     * If subType set to null, measureUnitImpl is in use instead of type and subType.
     * @internal
     * @deprecated This API is ICU internal only.
     */
    @Deprecated
    protected final String subType;

    /**
     * Used by new draft APIs in ICU 68.
     *
     * @internal
     */
    private MeasureUnitImpl measureUnitImpl;

    /**
     * Enumeration for unit complexity. There are three levels:
     * <p>
     * - SINGLE: A single unit, optionally with a power and/or SI prefix. Examples: hectare,
     * square-kilometer, kilojoule, one-per-second.
     * - COMPOUND: A unit composed of the product of multiple single units. Examples:
     * meter-per-second, kilowatt-hour, kilogram-meter-per-square-second.
     * - MIXED: A unit composed of the sum of multiple single units. Examples: foot-and-inch,
     * hour-and-minute-and-second, degree-and-arcminute-and-arcsecond.
     * <p>
     * The complexity determines which operations are available. For example, you cannot set the power
     * or SI prefix of a compound unit.
     *
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
     */
    public enum Complexity {
        /**
         * A single unit, like kilojoule.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        SINGLE,

        /**
         * A compound unit, like meter-per-second.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        COMPOUND,

        /**
         * A mixed unit, like hour-and-minute.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        MIXED
    }

    /**
     * Enumeration for SI prefixes, such as "kilo".
     *
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
     */
    public enum SIPrefix {

        /**
         * SI prefix: yotta, 10^24.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        YOTTA(24, "yotta"),

        /**
         * SI prefix: zetta, 10^21.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        ZETTA(21, "zetta"),

        /**
         * SI prefix: exa, 10^18.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        EXA(18, "exa"),

        /**
         * SI prefix: peta, 10^15.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        PETA(15, "peta"),

        /**
         * SI prefix: tera, 10^12.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        TERA(12, "tera"),

        /**
         * SI prefix: giga, 10^9.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        GIGA(9, "giga"),

        /**
         * SI prefix: mega, 10^6.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        MEGA(6, "mega"),

        /**
         * SI prefix: kilo, 10^3.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        KILO(3, "kilo"),

        /**
         * SI prefix: hecto, 10^2.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        HECTO(2, "hecto"),

        /**
         * SI prefix: deka, 10^1.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        DEKA(1, "deka"),

        /**
         * The absence of an SI prefix.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        ONE(0, ""),

        /**
         * SI prefix: deci, 10^-1.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        DECI(-1, "deci"),

        /**
         * SI prefix: centi, 10^-2.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        CENTI(-2, "centi"),

        /**
         * SI prefix: milli, 10^-3.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        MILLI(-3, "milli"),

        /**
         * SI prefix: micro, 10^-6.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        MICRO(-6, "micro"),

        /**
         * SI prefix: nano, 10^-9.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        NANO(-9, "nano"),

        /**
         * SI prefix: pico, 10^-12.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        PICO(-12, "pico"),

        /**
         * SI prefix: femto, 10^-15.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        FEMTO(-15, "femto"),

        /**
         * SI prefix: atto, 10^-18.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        ATTO(-18, "atto"),

        /**
         * SI prefix: zepto, 10^-21.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        ZEPTO(-21, "zepto"),

        /**
         * SI prefix: yocto, 10^-24.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        YOCTO(-24, "yocto");

        private final int power;
        private final String identifier;

        SIPrefix(int power, String identifier) {
            this.power = power;
            this.identifier = identifier;
        }

        /**
         * Returns the identifier of the prefix.
         *
         * @internal
         * @deprecated This API is ICU internal only.
         */
        @Deprecated
        public String getIdentifier() {
            return identifier;
        }

        /**
         * Returns the power of 10 of the prefix. For example, if the prefix is "centi", the power will be -2.
         *
         * @draft ICU 68
         * @provisional This API might change or be removed in a future release.
         */
        public int getPower() {
            return power;
        }
    }

    /**
     * @internal
     * @deprecated This API is ICU internal only.
     */
    @Deprecated
    protected MeasureUnit(String type, String subType) {
        this.type = type;
        this.subType = subType;
    }

    /**
     * Construct a MeasureUnit from a CLDR Unit Identifier, defined in UTS 35.
     * Validates and canonicalizes the identifier.
     *
     * Note: dimensionless <code>MeasureUnit</code> is <code>null</code>
     *
     * <pre>
     * MeasureUnit example = MeasureUnit::forIdentifier("furlong-per-nanosecond")
     * </pre>
     *
     * @param identifier The CLDR Sequence Unit Identifier
     * @throws IllegalArgumentException if the identifier is invalid.
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
     */
    public static MeasureUnit forIdentifier(String identifier) {
        if (identifier == null || identifier.isEmpty()) {
            return NoUnit.BASE;
        }

        return MeasureUnitImpl.forIdentifier(identifier).build();
    }

    /**
     * @internal
     * @deprecated Internal API for ICU use only.
     */
    @Deprecated
    public static MeasureUnit fromMeasureUnitImpl(MeasureUnitImpl measureUnitImpl) {
        measureUnitImpl.serialize();
        String identifier = measureUnitImpl.getIdentifier();
        MeasureUnit result = MeasureUnit.findBySubType(identifier);
        if (result != null) {
            return result;
        }

        return new MeasureUnit(measureUnitImpl);
    }

    private MeasureUnit(MeasureUnitImpl measureUnitImpl) {
        type = null;
        subType = null;
        this.measureUnitImpl = measureUnitImpl.copy();
    }


    /**
     * Get the type, such as "length". May return null.
     *
     * @stable ICU 53
     */
    public String getType() {
        return type;
    }


    /**
     * Get the subType, such as “foot”. May return null.
     *
     * @stable ICU 53
     */
    public String getSubtype() {
        return subType;
    }

    /**
     * Gets the CLDR Unit Identifier for this MeasureUnit, as defined in UTS 35.
     *
     * @return The string form of this unit.
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
     */
    public String getIdentifier() {
        String result = measureUnitImpl == null ? getSubtype() : measureUnitImpl.getIdentifier();
        return result == null ? "" : result;
    }

    /**
     * Compute the complexity of the unit. See Complexity for more information.
     *
     * @return The unit complexity.
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
     */
    public Complexity getComplexity() {
        if (measureUnitImpl == null) {
            return MeasureUnitImpl.forIdentifier(getIdentifier()).getComplexity();
        }

        return measureUnitImpl.getComplexity();
    }

    /**
     * Creates a MeasureUnit which is this SINGLE unit augmented with the specified SI prefix.
     * For example, SI_PREFIX_KILO for "kilo".
     * May return this if this unit already has that prefix.
     * <p>
     * There is sufficient locale data to format all standard SI prefixes.
     * <p>
     * NOTE: Only works on SINGLE units. If this is a COMPOUND or MIXED unit, an error will
     * occur. For more information, see `Complexity`.
     *
     * @param prefix The SI prefix, from SIPrefix.
     * @return A new SINGLE unit.
     * @throws UnsupportedOperationException if this unit is a COMPOUND or MIXED unit.
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
     */
    public MeasureUnit withSIPrefix(SIPrefix prefix) {
        SingleUnitImpl singleUnit = getSingleUnitImpl();
        singleUnit.setSiPrefix(prefix);
        return singleUnit.build();
    }

    /**
     * Returns the current SI prefix of this SINGLE unit. For example, if the unit has the SI prefix
     * "kilo", then SI_PREFIX_KILO is returned.
     * <p>
     * NOTE: Only works on SINGLE units. If this is a COMPOUND or MIXED unit, an error will
     * occur. For more information, see `Complexity`.
     *
     * @return The SI prefix of this SINGLE unit, from SIPrefix.
     * @throws UnsupportedOperationException if the unit is COMPOUND or MIXED.
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
     */
    public SIPrefix getSIPrefix() {
        return getSingleUnitImpl().getSiPrefix();
    }

    /**
     * Returns the dimensionality (power) of this MeasureUnit. For example, if the unit is square,
     * then 2 is returned.
     * <p>
     * NOTE: Only works on SINGLE units. If this is a COMPOUND or MIXED unit, an exception will be thrown.
     * For more information, see `Complexity`.
     *
     * @return The dimensionality (power) of this simple unit.
     * @throws UnsupportedOperationException if the unit is COMPOUND or MIXED.
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
     */
    public int getDimensionality() {
        return getSingleUnitImpl().getDimensionality();
    }

    /**
     * Creates a MeasureUnit which is this SINGLE unit augmented with the specified dimensionality
     * (power). For example, if dimensionality is 2, the unit will be squared.
     * <p>
     * NOTE: Only works on SINGLE units. If this is a COMPOUND or MIXED unit, an exception is thrown.
     * For more information, see `Complexity`.
     *
     * @param dimensionality The dimensionality (power).
     * @return A new SINGLE unit.
     * @throws UnsupportedOperationException if the unit is COMPOUND or MIXED.
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
     */
    public MeasureUnit withDimensionality(int dimensionality) {
        SingleUnitImpl singleUnit = getSingleUnitImpl();
        singleUnit.setDimensionality(dimensionality);
        return singleUnit.build();
    }

    /**
     * Computes the reciprocal of this MeasureUnit, with the numerator and denominator flipped.
     * <p>
     * For example, if the receiver is "meter-per-second", the unit "second-per-meter" is returned.
     * <p>
     * NOTE: Only works on SINGLE and COMPOUND units. If this is a MIXED unit, an error will
     * occur. For more information, see `Complexity`.
     *
     * @return The reciprocal of the target unit.
     * @throws UnsupportedOperationException if the unit is MIXED.
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
     */
    public MeasureUnit reciprocal() {
        MeasureUnitImpl measureUnit = getCopyOfMeasureUnitImpl();
        measureUnit.takeReciprocal();
        return measureUnit.build();
    }

    /**
     * Computes the product of this unit with another unit. This is a way to build units from
     * constituent parts.
     * <p>
     * The numerator and denominator are preserved through this operation.
     * <p>
     * For example, if the receiver is "kilowatt" and the argument is "hour-per-day", then the
     * unit "kilowatt-hour-per-day" is returned.
     * <p>
     * NOTE: Only works on SINGLE and COMPOUND units. If either unit (receivee and argument) is a
     * MIXED unit, an error will occur. For more information, see `Complexity`.
     *
     * @param other The MeasureUnit to multiply with the target.
     * @return The product of the target unit with the provided unit.
     * @throws UnsupportedOperationException if the unit is MIXED.
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
     */
    public MeasureUnit product(MeasureUnit other) {
        MeasureUnitImpl implCopy = getCopyOfMeasureUnitImpl();

        if (other == null /* dimensionless */) {
            return implCopy.build();
        }

        final MeasureUnitImpl otherImplRef = other.getMayBeReferenceOfMeasureUnitImpl();
        if (implCopy.getComplexity() == Complexity.MIXED || otherImplRef.getComplexity() == Complexity.MIXED) {
            throw new UnsupportedOperationException();
        }

        for (SingleUnitImpl singleUnit :
                otherImplRef.getSingleUnits()) {
            implCopy.appendSingleUnit(singleUnit);
        }

        return implCopy.build();
    }

    /**
     * Returns the list of SINGLE units contained within a sequence of COMPOUND units.
     * <p>
     * Examples:
     * - Given "meter-kilogram-per-second", three units will be returned: "meter",
     * "kilogram", and "one-per-second".
     * - Given "hour+minute+second", three units will be returned: "hour", "minute",
     * and "second".
     * <p>
     * If this is a SINGLE unit, a list of length 1 will be returned.
     *
     * @return An unmodifiable list of single units
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
     */
    public List<MeasureUnit> splitToSingleUnits() {
        final ArrayList<SingleUnitImpl> singleUnits = getMayBeReferenceOfMeasureUnitImpl().getSingleUnits();
        List<MeasureUnit> result = new ArrayList<>(singleUnits.size());
        for (SingleUnitImpl singleUnit : singleUnits) {
            result.add(singleUnit.build());
        }

        return result;
    }

    /**
     * {@inheritDoc}
     *
     * @stable ICU 3.0
     */
    @Override
    public int hashCode() {
        return 31 * type.hashCode() + subType.hashCode();
    }

    /**
     * {@inheritDoc}
     *
     * @stable ICU 3.0
     */
    @Override
    public boolean equals(Object rhs) {
        if (rhs == this) {
            return true;
        }
        if (!(rhs instanceof MeasureUnit)) {
            return false;
        }

        return this.getIdentifier().equals(((MeasureUnit) rhs).getIdentifier());
    }

    /**
     * {@inheritDoc}
     *
     * @stable ICU 3.0
     */
    @Override
    public String toString() {
        return type + "-" + subType;
    }

    /**
     * Get all of the available units' types. Returned set is unmodifiable.
     *
     * @stable ICU 53
     */
    public synchronized static Set<String> getAvailableTypes() {
        populateCache();
        return Collections.unmodifiableSet(cache.keySet());
    }

    /**
     * For the given type, return the available units.
     * @param type the type
     * @return the available units for type. Returned set is unmodifiable.
     * @stable ICU 53
     */
    public synchronized static Set<MeasureUnit> getAvailable(String type) {
        populateCache();
        Map<String, MeasureUnit> units = cache.get(type);
        // Train users not to modify returned set from the start giving us more
        // flexibility for implementation.
        // Use CollectionSet instead of HashSet for better performance.
        return units == null ? Collections.<MeasureUnit>emptySet()
                : Collections.unmodifiableSet(new CollectionSet<>(units.values()));
    }

    /**
     * Get all of the available units. Returned set is unmodifiable.
     *
     * @stable ICU 53
     */
    public synchronized static Set<MeasureUnit> getAvailable() {
        Set<MeasureUnit> result = new HashSet<>();
        for (String type : new HashSet<>(MeasureUnit.getAvailableTypes())) {
            for (MeasureUnit unit : MeasureUnit.getAvailable(type)) {
                result.add(unit);
            }
        }
        // Train users not to modify returned set from the start giving us more
        // flexibility for implementation.
        return Collections.unmodifiableSet(result);
    }

    /**
     * Creates a MeasureUnit instance (creates a singleton instance) or returns one from the cache.
     * <p>
     * Normally this method should not be used, since there will be no formatting data
     * available for it, and it may not be returned by getAvailable().
     * However, for special purposes (such as CLDR tooling), it is available.
     *
     * @internal
     * @deprecated This API is ICU internal only.
     */
    @Deprecated
    public static MeasureUnit internalGetInstance(String type, String subType) {
        if (type == null || subType == null) {
            throw new NullPointerException("Type and subType must be non-null");
        }
        if (!"currency".equals(type)) {
            if (!ASCII.containsAll(type) || !ASCII_HYPHEN_DIGITS.containsAll(subType)) {
                throw new IllegalArgumentException("The type or subType are invalid.");
            }
        }
        Factory factory;
        if ("currency".equals(type)) {
            factory = CURRENCY_FACTORY;
        } else if ("duration".equals(type)) {
            factory = TIMEUNIT_FACTORY;
        } else {
            factory = UNIT_FACTORY;
        }
        return MeasureUnit.addUnit(type, subType, factory);
    }

    private static MeasureUnit findBySubType(String subType) {
        populateCache();
        for (Map<String, MeasureUnit> unitsForType : cache.values()) {
            if (unitsForType.containsKey(subType)) {
                return unitsForType.get(subType);
            }
        }
        return null;
    }

    static final UnicodeSet ASCII = new UnicodeSet('a', 'z').freeze();
    static final UnicodeSet ASCII_HYPHEN_DIGITS = new UnicodeSet('-', '-', '0', '9', 'a', 'z').freeze();

    /**
     * @internal
     * @deprecated This API is ICU internal only.
     */
    @Deprecated
    protected interface Factory {
        /**
         * @internal
         * @deprecated This API is ICU internal only.
         */
        @Deprecated
        MeasureUnit create(String type, String subType);
    }

    private static Factory UNIT_FACTORY = new Factory() {
        @Override
        public MeasureUnit create(String type, String subType) {
            return new MeasureUnit(type, subType);
        }
    };

    static Factory CURRENCY_FACTORY = new Factory() {
        @Override
        public MeasureUnit create(String unusedType, String subType) {
            return new Currency(subType);
        }
    };

    static Factory TIMEUNIT_FACTORY = new Factory() {
        @Override
        public MeasureUnit create(String type, String subType) {
           return new TimeUnit(type, subType);
        }
    };

    /**
     * Sink for enumerating the available measure units.
     */
    private static final class MeasureUnitSink extends UResource.Sink {
        @Override
        public void put(UResource.Key key, UResource.Value value, boolean noFallback) {
            UResource.Table unitTypesTable = value.getTable();
            for (int i2 = 0; unitTypesTable.getKeyAndValue(i2, key, value); ++i2) {
                // Skip "compound" and "coordinate" since they are treated differently from the other units
                if (key.contentEquals("compound") || key.contentEquals("coordinate")) {
                    continue;
                }

                String unitType = key.toString();
                UResource.Table unitNamesTable = value.getTable();
                for (int i3 = 0; unitNamesTable.getKeyAndValue(i3, key, value); ++i3) {
                    String unitName = key.toString();
                    internalGetInstance(unitType, unitName);
                }
            }
        }
    }

    /**
     * Sink for enumerating the currency numeric codes.
     */
    private static final class CurrencyNumericCodeSink extends UResource.Sink {
        @Override
        public void put(UResource.Key key, UResource.Value value, boolean noFallback) {
            UResource.Table codesTable = value.getTable();
            for (int i1 = 0; codesTable.getKeyAndValue(i1, key, value); ++i1) {
                internalGetInstance("currency", key.toString());
            }
        }
    }

    /**
     * Populate the MeasureUnit cache with all types from the data.
     * Population is done lazily, in response to MeasureUnit.getAvailable()
     * or other API that expects to see all of the MeasureUnits.
     *
     * <p>At static initialization time the MeasureUnits cache is populated
     * with public static instances (G_FORCE, METER_PER_SECOND_SQUARED, etc.) only.
     * Adding of others is deferred until later to avoid circular static init
     * dependencies with classes Currency and TimeUnit.
     *
     * <p>Synchronization: this function must be called from static synchronized methods only.
     *
     * @internal
     */
    static private void populateCache() {
        if (cacheIsPopulated) {
            return;
        }
        cacheIsPopulated = true;

        /*  Schema:
         *
         *  units{
         *    duration{
         *      day{
         *        one{"{0} ден"}
         *        other{"{0} дена"}
         *      }
         */

        // Load the unit types.  Use English, since we know that that is a superset.
        ICUResourceBundle rb1 = (ICUResourceBundle) UResourceBundle.getBundleInstance(
                ICUData.ICU_UNIT_BASE_NAME,
                "en");
        rb1.getAllItemsWithFallback("units", new MeasureUnitSink());

        // Load the currencies
        ICUResourceBundle rb2 = (ICUResourceBundle) UResourceBundle.getBundleInstance(
                ICUData.ICU_BASE_NAME,
                "currencyNumericCodes",
                ICUResourceBundle.ICU_DATA_CLASS_LOADER);
        rb2.getAllItemsWithFallback("codeMap", new CurrencyNumericCodeSink());
    }

    /**
     * @internal
     * @deprecated This API is ICU internal only.
     */
    @Deprecated
    protected synchronized static MeasureUnit addUnit(String type, String unitName, Factory factory) {
        Map<String, MeasureUnit> tmp = cache.get(type);
        if (tmp == null) {
            cache.put(type, tmp = new HashMap<>());
        } else {
            // "intern" the type by setting to first item's type.
            type = tmp.entrySet().iterator().next().getValue().type;
        }
        MeasureUnit unit = tmp.get(unitName);
        if (unit == null) {
            tmp.put(unitName, unit = factory.create(type, unitName));
        }
        return unit;
    }


    /*
     * Useful constants. Not necessarily complete: see {@link #getAvailable()}.
     */

// All code between the "Start generated MeasureUnit constants" comment and
// the "End generated MeasureUnit constants" comment is auto generated code
// and must not be edited manually. For instructions on how to correctly
// update this code, refer to:
// http://site.icu-project.org/design/formatting/measureformat/updating-measure-unit
//
    // Start generated MeasureUnit constants

    /**
     * Constant for unit of acceleration: g-force
     * @stable ICU 53
     */
    public static final MeasureUnit G_FORCE = MeasureUnit.internalGetInstance("acceleration", "g-force");

    /**
     * Constant for unit of acceleration: meter-per-square-second
     * @stable ICU 54
     */
    public static final MeasureUnit METER_PER_SECOND_SQUARED = MeasureUnit.internalGetInstance("acceleration", "meter-per-square-second");

    /**
     * Constant for unit of angle: arc-minute
     * @stable ICU 53
     */
    public static final MeasureUnit ARC_MINUTE = MeasureUnit.internalGetInstance("angle", "arc-minute");

    /**
     * Constant for unit of angle: arc-second
     * @stable ICU 53
     */
    public static final MeasureUnit ARC_SECOND = MeasureUnit.internalGetInstance("angle", "arc-second");

    /**
     * Constant for unit of angle: degree
     * @stable ICU 53
     */
    public static final MeasureUnit DEGREE = MeasureUnit.internalGetInstance("angle", "degree");

    /**
     * Constant for unit of angle: radian
     * @stable ICU 54
     */
    public static final MeasureUnit RADIAN = MeasureUnit.internalGetInstance("angle", "radian");

    /**
     * Constant for unit of angle: revolution
     * @stable ICU 56
     */
    public static final MeasureUnit REVOLUTION_ANGLE = MeasureUnit.internalGetInstance("angle", "revolution");

    /**
     * Constant for unit of area: acre
     * @stable ICU 53
     */
    public static final MeasureUnit ACRE = MeasureUnit.internalGetInstance("area", "acre");

    /**
     * Constant for unit of area: dunam
     * @stable ICU 64
     */
    public static final MeasureUnit DUNAM = MeasureUnit.internalGetInstance("area", "dunam");

    /**
     * Constant for unit of area: hectare
     * @stable ICU 53
     */
    public static final MeasureUnit HECTARE = MeasureUnit.internalGetInstance("area", "hectare");

    /**
     * Constant for unit of area: square-centimeter
     * @stable ICU 54
     */
    public static final MeasureUnit SQUARE_CENTIMETER = MeasureUnit.internalGetInstance("area", "square-centimeter");

    /**
     * Constant for unit of area: square-foot
     * @stable ICU 53
     */
    public static final MeasureUnit SQUARE_FOOT = MeasureUnit.internalGetInstance("area", "square-foot");

    /**
     * Constant for unit of area: square-inch
     * @stable ICU 54
     */
    public static final MeasureUnit SQUARE_INCH = MeasureUnit.internalGetInstance("area", "square-inch");

    /**
     * Constant for unit of area: square-kilometer
     * @stable ICU 53
     */
    public static final MeasureUnit SQUARE_KILOMETER = MeasureUnit.internalGetInstance("area", "square-kilometer");

    /**
     * Constant for unit of area: square-meter
     * @stable ICU 53
     */
    public static final MeasureUnit SQUARE_METER = MeasureUnit.internalGetInstance("area", "square-meter");

    /**
     * Constant for unit of area: square-mile
     * @stable ICU 53
     */
    public static final MeasureUnit SQUARE_MILE = MeasureUnit.internalGetInstance("area", "square-mile");

    /**
     * Constant for unit of area: square-yard
     * @stable ICU 54
     */
    public static final MeasureUnit SQUARE_YARD = MeasureUnit.internalGetInstance("area", "square-yard");

    /**
     * Constant for unit of concentr: karat
     * @stable ICU 54
     */
    public static final MeasureUnit KARAT = MeasureUnit.internalGetInstance("concentr", "karat");

    /**
     * Constant for unit of concentr: milligram-per-deciliter
     * @stable ICU 57
     */
    public static final MeasureUnit MILLIGRAM_PER_DECILITER = MeasureUnit.internalGetInstance("concentr", "milligram-per-deciliter");

    /**
     * Constant for unit of concentr: millimole-per-liter
     * @stable ICU 57
     */
    public static final MeasureUnit MILLIMOLE_PER_LITER = MeasureUnit.internalGetInstance("concentr", "millimole-per-liter");

    /**
     * Constant for unit of concentr: mole
     * @stable ICU 64
     */
    public static final MeasureUnit MOLE = MeasureUnit.internalGetInstance("concentr", "mole");

    /**
     * Constant for unit of concentr: percent
     * @stable ICU 63
     */
    public static final MeasureUnit PERCENT = MeasureUnit.internalGetInstance("concentr", "percent");

    /**
     * Constant for unit of concentr: permille
     * @stable ICU 63
     */
    public static final MeasureUnit PERMILLE = MeasureUnit.internalGetInstance("concentr", "permille");

    /**
     * Constant for unit of concentr: permillion
     * @stable ICU 57
     */
    public static final MeasureUnit PART_PER_MILLION = MeasureUnit.internalGetInstance("concentr", "permillion");

    /**
     * Constant for unit of concentr: permyriad
     * @stable ICU 64
     */
    public static final MeasureUnit PERMYRIAD = MeasureUnit.internalGetInstance("concentr", "permyriad");

    /**
     * Constant for unit of consumption: liter-per-100-kilometer
     * @stable ICU 56
     */
    public static final MeasureUnit LITER_PER_100KILOMETERS = MeasureUnit.internalGetInstance("consumption", "liter-per-100-kilometer");

    /**
     * Constant for unit of consumption: liter-per-kilometer
     * @stable ICU 54
     */
    public static final MeasureUnit LITER_PER_KILOMETER = MeasureUnit.internalGetInstance("consumption", "liter-per-kilometer");

    /**
     * Constant for unit of consumption: mile-per-gallon
     * @stable ICU 54
     */
    public static final MeasureUnit MILE_PER_GALLON = MeasureUnit.internalGetInstance("consumption", "mile-per-gallon");

    /**
     * Constant for unit of consumption: mile-per-gallon-imperial
     * @stable ICU 57
     */
    public static final MeasureUnit MILE_PER_GALLON_IMPERIAL = MeasureUnit.internalGetInstance("consumption", "mile-per-gallon-imperial");

    /**
     * Constant for unit of digital: bit
     * @stable ICU 54
     */
    public static final MeasureUnit BIT = MeasureUnit.internalGetInstance("digital", "bit");

    /**
     * Constant for unit of digital: byte
     * @stable ICU 54
     */
    public static final MeasureUnit BYTE = MeasureUnit.internalGetInstance("digital", "byte");

    /**
     * Constant for unit of digital: gigabit
     * @stable ICU 54
     */
    public static final MeasureUnit GIGABIT = MeasureUnit.internalGetInstance("digital", "gigabit");

    /**
     * Constant for unit of digital: gigabyte
     * @stable ICU 54
     */
    public static final MeasureUnit GIGABYTE = MeasureUnit.internalGetInstance("digital", "gigabyte");

    /**
     * Constant for unit of digital: kilobit
     * @stable ICU 54
     */
    public static final MeasureUnit KILOBIT = MeasureUnit.internalGetInstance("digital", "kilobit");

    /**
     * Constant for unit of digital: kilobyte
     * @stable ICU 54
     */
    public static final MeasureUnit KILOBYTE = MeasureUnit.internalGetInstance("digital", "kilobyte");

    /**
     * Constant for unit of digital: megabit
     * @stable ICU 54
     */
    public static final MeasureUnit MEGABIT = MeasureUnit.internalGetInstance("digital", "megabit");

    /**
     * Constant for unit of digital: megabyte
     * @stable ICU 54
     */
    public static final MeasureUnit MEGABYTE = MeasureUnit.internalGetInstance("digital", "megabyte");

    /**
     * Constant for unit of digital: petabyte
     * @stable ICU 63
     */
    public static final MeasureUnit PETABYTE = MeasureUnit.internalGetInstance("digital", "petabyte");

    /**
     * Constant for unit of digital: terabit
     * @stable ICU 54
     */
    public static final MeasureUnit TERABIT = MeasureUnit.internalGetInstance("digital", "terabit");

    /**
     * Constant for unit of digital: terabyte
     * @stable ICU 54
     */
    public static final MeasureUnit TERABYTE = MeasureUnit.internalGetInstance("digital", "terabyte");

    /**
     * Constant for unit of duration: century
     * @stable ICU 56
     */
    public static final MeasureUnit CENTURY = MeasureUnit.internalGetInstance("duration", "century");

    /**
     * Constant for unit of duration: day
     * @stable ICU 4.0
     */
    public static final TimeUnit DAY = (TimeUnit) MeasureUnit.internalGetInstance("duration", "day");

    /**
     * Constant for unit of duration: day-person
     * @stable ICU 64
     */
    public static final MeasureUnit DAY_PERSON = MeasureUnit.internalGetInstance("duration", "day-person");

    /**
     * Constant for unit of duration: decade
     * @stable ICU 65
     */
    public static final MeasureUnit DECADE = MeasureUnit.internalGetInstance("duration", "decade");

    /**
     * Constant for unit of duration: hour
     * @stable ICU 4.0
     */
    public static final TimeUnit HOUR = (TimeUnit) MeasureUnit.internalGetInstance("duration", "hour");

    /**
     * Constant for unit of duration: microsecond
     * @stable ICU 54
     */
    public static final MeasureUnit MICROSECOND = MeasureUnit.internalGetInstance("duration", "microsecond");

    /**
     * Constant for unit of duration: millisecond
     * @stable ICU 53
     */
    public static final MeasureUnit MILLISECOND = MeasureUnit.internalGetInstance("duration", "millisecond");

    /**
     * Constant for unit of duration: minute
     * @stable ICU 4.0
     */
    public static final TimeUnit MINUTE = (TimeUnit) MeasureUnit.internalGetInstance("duration", "minute");

    /**
     * Constant for unit of duration: month
     * @stable ICU 4.0
     */
    public static final TimeUnit MONTH = (TimeUnit) MeasureUnit.internalGetInstance("duration", "month");

    /**
     * Constant for unit of duration: month-person
     * @stable ICU 64
     */
    public static final MeasureUnit MONTH_PERSON = MeasureUnit.internalGetInstance("duration", "month-person");

    /**
     * Constant for unit of duration: nanosecond
     * @stable ICU 54
     */
    public static final MeasureUnit NANOSECOND = MeasureUnit.internalGetInstance("duration", "nanosecond");

    /**
     * Constant for unit of duration: second
     * @stable ICU 4.0
     */
    public static final TimeUnit SECOND = (TimeUnit) MeasureUnit.internalGetInstance("duration", "second");

    /**
     * Constant for unit of duration: week
     * @stable ICU 4.0
     */
    public static final TimeUnit WEEK = (TimeUnit) MeasureUnit.internalGetInstance("duration", "week");

    /**
     * Constant for unit of duration: week-person
     * @stable ICU 64
     */
    public static final MeasureUnit WEEK_PERSON = MeasureUnit.internalGetInstance("duration", "week-person");

    /**
     * Constant for unit of duration: year
     * @stable ICU 4.0
     */
    public static final TimeUnit YEAR = (TimeUnit) MeasureUnit.internalGetInstance("duration", "year");

    /**
     * Constant for unit of duration: year-person
     * @stable ICU 64
     */
    public static final MeasureUnit YEAR_PERSON = MeasureUnit.internalGetInstance("duration", "year-person");

    /**
     * Constant for unit of electric: ampere
     * @stable ICU 54
     */
    public static final MeasureUnit AMPERE = MeasureUnit.internalGetInstance("electric", "ampere");

    /**
     * Constant for unit of electric: milliampere
     * @stable ICU 54
     */
    public static final MeasureUnit MILLIAMPERE = MeasureUnit.internalGetInstance("electric", "milliampere");

    /**
     * Constant for unit of electric: ohm
     * @stable ICU 54
     */
    public static final MeasureUnit OHM = MeasureUnit.internalGetInstance("electric", "ohm");

    /**
     * Constant for unit of electric: volt
     * @stable ICU 54
     */
    public static final MeasureUnit VOLT = MeasureUnit.internalGetInstance("electric", "volt");

    /**
     * Constant for unit of energy: british-thermal-unit
     * @stable ICU 64
     */
    public static final MeasureUnit BRITISH_THERMAL_UNIT = MeasureUnit.internalGetInstance("energy", "british-thermal-unit");

    /**
     * Constant for unit of energy: calorie
     * @stable ICU 54
     */
    public static final MeasureUnit CALORIE = MeasureUnit.internalGetInstance("energy", "calorie");

    /**
     * Constant for unit of energy: electronvolt
     * @stable ICU 64
     */
    public static final MeasureUnit ELECTRONVOLT = MeasureUnit.internalGetInstance("energy", "electronvolt");

    /**
     * Constant for unit of energy: foodcalorie
     * @stable ICU 54
     */
    public static final MeasureUnit FOODCALORIE = MeasureUnit.internalGetInstance("energy", "foodcalorie");

    /**
     * Constant for unit of energy: joule
     * @stable ICU 54
     */
    public static final MeasureUnit JOULE = MeasureUnit.internalGetInstance("energy", "joule");

    /**
     * Constant for unit of energy: kilocalorie
     * @stable ICU 54
     */
    public static final MeasureUnit KILOCALORIE = MeasureUnit.internalGetInstance("energy", "kilocalorie");

    /**
     * Constant for unit of energy: kilojoule
     * @stable ICU 54
     */
    public static final MeasureUnit KILOJOULE = MeasureUnit.internalGetInstance("energy", "kilojoule");

    /**
     * Constant for unit of energy: kilowatt-hour
     * @stable ICU 54
     */
    public static final MeasureUnit KILOWATT_HOUR = MeasureUnit.internalGetInstance("energy", "kilowatt-hour");

    /**
     * Constant for unit of energy: therm-us
     * @stable ICU 65
     */
    public static final MeasureUnit THERM_US = MeasureUnit.internalGetInstance("energy", "therm-us");

    /**
     * Constant for unit of force: newton
     * @stable ICU 64
     */
    public static final MeasureUnit NEWTON = MeasureUnit.internalGetInstance("force", "newton");

    /**
     * Constant for unit of force: pound-force
     * @stable ICU 64
     */
    public static final MeasureUnit POUND_FORCE = MeasureUnit.internalGetInstance("force", "pound-force");

    /**
     * Constant for unit of frequency: gigahertz
     * @stable ICU 54
     */
    public static final MeasureUnit GIGAHERTZ = MeasureUnit.internalGetInstance("frequency", "gigahertz");

    /**
     * Constant for unit of frequency: hertz
     * @stable ICU 54
     */
    public static final MeasureUnit HERTZ = MeasureUnit.internalGetInstance("frequency", "hertz");

    /**
     * Constant for unit of frequency: kilohertz
     * @stable ICU 54
     */
    public static final MeasureUnit KILOHERTZ = MeasureUnit.internalGetInstance("frequency", "kilohertz");

    /**
     * Constant for unit of frequency: megahertz
     * @stable ICU 54
     */
    public static final MeasureUnit MEGAHERTZ = MeasureUnit.internalGetInstance("frequency", "megahertz");

    /**
     * Constant for unit of graphics: dot
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
    */
    public static final MeasureUnit DOT = MeasureUnit.internalGetInstance("graphics", "dot");

    /**
     * Constant for unit of graphics: dot-per-centimeter
     * @stable ICU 65
     */
    public static final MeasureUnit DOT_PER_CENTIMETER = MeasureUnit.internalGetInstance("graphics", "dot-per-centimeter");

    /**
     * Constant for unit of graphics: dot-per-inch
     * @stable ICU 65
     */
    public static final MeasureUnit DOT_PER_INCH = MeasureUnit.internalGetInstance("graphics", "dot-per-inch");

    /**
     * Constant for unit of graphics: em
     * @stable ICU 65
     */
    public static final MeasureUnit EM = MeasureUnit.internalGetInstance("graphics", "em");

    /**
     * Constant for unit of graphics: megapixel
     * @stable ICU 65
     */
    public static final MeasureUnit MEGAPIXEL = MeasureUnit.internalGetInstance("graphics", "megapixel");

    /**
     * Constant for unit of graphics: pixel
     * @stable ICU 65
     */
    public static final MeasureUnit PIXEL = MeasureUnit.internalGetInstance("graphics", "pixel");

    /**
     * Constant for unit of graphics: pixel-per-centimeter
     * @stable ICU 65
     */
    public static final MeasureUnit PIXEL_PER_CENTIMETER = MeasureUnit.internalGetInstance("graphics", "pixel-per-centimeter");

    /**
     * Constant for unit of graphics: pixel-per-inch
     * @stable ICU 65
     */
    public static final MeasureUnit PIXEL_PER_INCH = MeasureUnit.internalGetInstance("graphics", "pixel-per-inch");

    /**
     * Constant for unit of length: astronomical-unit
     * @stable ICU 54
     */
    public static final MeasureUnit ASTRONOMICAL_UNIT = MeasureUnit.internalGetInstance("length", "astronomical-unit");

    /**
     * Constant for unit of length: centimeter
     * @stable ICU 53
     */
    public static final MeasureUnit CENTIMETER = MeasureUnit.internalGetInstance("length", "centimeter");

    /**
     * Constant for unit of length: decimeter
     * @stable ICU 54
     */
    public static final MeasureUnit DECIMETER = MeasureUnit.internalGetInstance("length", "decimeter");

    /**
     * Constant for unit of length: earth-radius
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
    */
    public static final MeasureUnit EARTH_RADIUS = MeasureUnit.internalGetInstance("length", "earth-radius");

    /**
     * Constant for unit of length: fathom
     * @stable ICU 54
     */
    public static final MeasureUnit FATHOM = MeasureUnit.internalGetInstance("length", "fathom");

    /**
     * Constant for unit of length: foot
     * @stable ICU 53
     */
    public static final MeasureUnit FOOT = MeasureUnit.internalGetInstance("length", "foot");

    /**
     * Constant for unit of length: furlong
     * @stable ICU 54
     */
    public static final MeasureUnit FURLONG = MeasureUnit.internalGetInstance("length", "furlong");

    /**
     * Constant for unit of length: inch
     * @stable ICU 53
     */
    public static final MeasureUnit INCH = MeasureUnit.internalGetInstance("length", "inch");

    /**
     * Constant for unit of length: kilometer
     * @stable ICU 53
     */
    public static final MeasureUnit KILOMETER = MeasureUnit.internalGetInstance("length", "kilometer");

    /**
     * Constant for unit of length: light-year
     * @stable ICU 53
     */
    public static final MeasureUnit LIGHT_YEAR = MeasureUnit.internalGetInstance("length", "light-year");

    /**
     * Constant for unit of length: meter
     * @stable ICU 53
     */
    public static final MeasureUnit METER = MeasureUnit.internalGetInstance("length", "meter");

    /**
     * Constant for unit of length: micrometer
     * @stable ICU 54
     */
    public static final MeasureUnit MICROMETER = MeasureUnit.internalGetInstance("length", "micrometer");

    /**
     * Constant for unit of length: mile
     * @stable ICU 53
     */
    public static final MeasureUnit MILE = MeasureUnit.internalGetInstance("length", "mile");

    /**
     * Constant for unit of length: mile-scandinavian
     * @stable ICU 56
     */
    public static final MeasureUnit MILE_SCANDINAVIAN = MeasureUnit.internalGetInstance("length", "mile-scandinavian");

    /**
     * Constant for unit of length: millimeter
     * @stable ICU 53
     */
    public static final MeasureUnit MILLIMETER = MeasureUnit.internalGetInstance("length", "millimeter");

    /**
     * Constant for unit of length: nanometer
     * @stable ICU 54
     */
    public static final MeasureUnit NANOMETER = MeasureUnit.internalGetInstance("length", "nanometer");

    /**
     * Constant for unit of length: nautical-mile
     * @stable ICU 54
     */
    public static final MeasureUnit NAUTICAL_MILE = MeasureUnit.internalGetInstance("length", "nautical-mile");

    /**
     * Constant for unit of length: parsec
     * @stable ICU 54
     */
    public static final MeasureUnit PARSEC = MeasureUnit.internalGetInstance("length", "parsec");

    /**
     * Constant for unit of length: picometer
     * @stable ICU 53
     */
    public static final MeasureUnit PICOMETER = MeasureUnit.internalGetInstance("length", "picometer");

    /**
     * Constant for unit of length: point
     * @stable ICU 59
     */
    public static final MeasureUnit POINT = MeasureUnit.internalGetInstance("length", "point");

    /**
     * Constant for unit of length: solar-radius
     * @stable ICU 64
     */
    public static final MeasureUnit SOLAR_RADIUS = MeasureUnit.internalGetInstance("length", "solar-radius");

    /**
     * Constant for unit of length: yard
     * @stable ICU 53
     */
    public static final MeasureUnit YARD = MeasureUnit.internalGetInstance("length", "yard");

    /**
     * Constant for unit of light: candela
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
    */
    public static final MeasureUnit CANDELA = MeasureUnit.internalGetInstance("light", "candela");

    /**
     * Constant for unit of light: lumen
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
    */
    public static final MeasureUnit LUMEN = MeasureUnit.internalGetInstance("light", "lumen");

    /**
     * Constant for unit of light: lux
     * @stable ICU 54
     */
    public static final MeasureUnit LUX = MeasureUnit.internalGetInstance("light", "lux");

    /**
     * Constant for unit of light: solar-luminosity
     * @stable ICU 64
     */
    public static final MeasureUnit SOLAR_LUMINOSITY = MeasureUnit.internalGetInstance("light", "solar-luminosity");

    /**
     * Constant for unit of mass: carat
     * @stable ICU 54
     */
    public static final MeasureUnit CARAT = MeasureUnit.internalGetInstance("mass", "carat");

    /**
     * Constant for unit of mass: dalton
     * @stable ICU 64
     */
    public static final MeasureUnit DALTON = MeasureUnit.internalGetInstance("mass", "dalton");

    /**
     * Constant for unit of mass: earth-mass
     * @stable ICU 64
     */
    public static final MeasureUnit EARTH_MASS = MeasureUnit.internalGetInstance("mass", "earth-mass");

    /**
     * Constant for unit of mass: grain
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
    */
    public static final MeasureUnit GRAIN = MeasureUnit.internalGetInstance("mass", "grain");

    /**
     * Constant for unit of mass: gram
     * @stable ICU 53
     */
    public static final MeasureUnit GRAM = MeasureUnit.internalGetInstance("mass", "gram");

    /**
     * Constant for unit of mass: kilogram
     * @stable ICU 53
     */
    public static final MeasureUnit KILOGRAM = MeasureUnit.internalGetInstance("mass", "kilogram");

    /**
     * Constant for unit of mass: metric-ton
     * @stable ICU 54
     */
    public static final MeasureUnit METRIC_TON = MeasureUnit.internalGetInstance("mass", "metric-ton");

    /**
     * Constant for unit of mass: microgram
     * @stable ICU 54
     */
    public static final MeasureUnit MICROGRAM = MeasureUnit.internalGetInstance("mass", "microgram");

    /**
     * Constant for unit of mass: milligram
     * @stable ICU 54
     */
    public static final MeasureUnit MILLIGRAM = MeasureUnit.internalGetInstance("mass", "milligram");

    /**
     * Constant for unit of mass: ounce
     * @stable ICU 53
     */
    public static final MeasureUnit OUNCE = MeasureUnit.internalGetInstance("mass", "ounce");

    /**
     * Constant for unit of mass: ounce-troy
     * @stable ICU 54
     */
    public static final MeasureUnit OUNCE_TROY = MeasureUnit.internalGetInstance("mass", "ounce-troy");

    /**
     * Constant for unit of mass: pound
     * @stable ICU 53
     */
    public static final MeasureUnit POUND = MeasureUnit.internalGetInstance("mass", "pound");

    /**
     * Constant for unit of mass: solar-mass
     * @stable ICU 64
     */
    public static final MeasureUnit SOLAR_MASS = MeasureUnit.internalGetInstance("mass", "solar-mass");

    /**
     * Constant for unit of mass: stone
     * @stable ICU 54
     */
    public static final MeasureUnit STONE = MeasureUnit.internalGetInstance("mass", "stone");

    /**
     * Constant for unit of mass: ton
     * @stable ICU 54
     */
    public static final MeasureUnit TON = MeasureUnit.internalGetInstance("mass", "ton");

    /**
     * Constant for unit of power: gigawatt
     * @stable ICU 54
     */
    public static final MeasureUnit GIGAWATT = MeasureUnit.internalGetInstance("power", "gigawatt");

    /**
     * Constant for unit of power: horsepower
     * @stable ICU 53
     */
    public static final MeasureUnit HORSEPOWER = MeasureUnit.internalGetInstance("power", "horsepower");

    /**
     * Constant for unit of power: kilowatt
     * @stable ICU 53
     */
    public static final MeasureUnit KILOWATT = MeasureUnit.internalGetInstance("power", "kilowatt");

    /**
     * Constant for unit of power: megawatt
     * @stable ICU 54
     */
    public static final MeasureUnit MEGAWATT = MeasureUnit.internalGetInstance("power", "megawatt");

    /**
     * Constant for unit of power: milliwatt
     * @stable ICU 54
     */
    public static final MeasureUnit MILLIWATT = MeasureUnit.internalGetInstance("power", "milliwatt");

    /**
     * Constant for unit of power: watt
     * @stable ICU 53
     */
    public static final MeasureUnit WATT = MeasureUnit.internalGetInstance("power", "watt");

    /**
     * Constant for unit of pressure: atmosphere
     * @stable ICU 63
     */
    public static final MeasureUnit ATMOSPHERE = MeasureUnit.internalGetInstance("pressure", "atmosphere");

    /**
     * Constant for unit of pressure: bar
     * @stable ICU 65
     */
    public static final MeasureUnit BAR = MeasureUnit.internalGetInstance("pressure", "bar");

    /**
     * Constant for unit of pressure: hectopascal
     * @stable ICU 53
     */
    public static final MeasureUnit HECTOPASCAL = MeasureUnit.internalGetInstance("pressure", "hectopascal");

    /**
     * Constant for unit of pressure: inch-ofhg
     * @stable ICU 53
     */
    public static final MeasureUnit INCH_HG = MeasureUnit.internalGetInstance("pressure", "inch-ofhg");

    /**
     * Constant for unit of pressure: kilopascal
     * @stable ICU 64
     */
    public static final MeasureUnit KILOPASCAL = MeasureUnit.internalGetInstance("pressure", "kilopascal");

    /**
     * Constant for unit of pressure: megapascal
     * @stable ICU 64
     */
    public static final MeasureUnit MEGAPASCAL = MeasureUnit.internalGetInstance("pressure", "megapascal");

    /**
     * Constant for unit of pressure: millibar
     * @stable ICU 53
     */
    public static final MeasureUnit MILLIBAR = MeasureUnit.internalGetInstance("pressure", "millibar");

    /**
     * Constant for unit of pressure: millimeter-ofhg
     * @stable ICU 54
     */
    public static final MeasureUnit MILLIMETER_OF_MERCURY = MeasureUnit.internalGetInstance("pressure", "millimeter-ofhg");

    /**
     * Constant for unit of pressure: pascal
     * @stable ICU 65
     */
    public static final MeasureUnit PASCAL = MeasureUnit.internalGetInstance("pressure", "pascal");

    /**
     * Constant for unit of pressure: pound-force-per-square-inch
     * @stable ICU 54
     */
    public static final MeasureUnit POUND_PER_SQUARE_INCH = MeasureUnit.internalGetInstance("pressure", "pound-force-per-square-inch");

    /**
     * Constant for unit of speed: kilometer-per-hour
     * @stable ICU 53
     */
    public static final MeasureUnit KILOMETER_PER_HOUR = MeasureUnit.internalGetInstance("speed", "kilometer-per-hour");

    /**
     * Constant for unit of speed: knot
     * @stable ICU 56
     */
    public static final MeasureUnit KNOT = MeasureUnit.internalGetInstance("speed", "knot");

    /**
     * Constant for unit of speed: meter-per-second
     * @stable ICU 53
     */
    public static final MeasureUnit METER_PER_SECOND = MeasureUnit.internalGetInstance("speed", "meter-per-second");

    /**
     * Constant for unit of speed: mile-per-hour
     * @stable ICU 53
     */
    public static final MeasureUnit MILE_PER_HOUR = MeasureUnit.internalGetInstance("speed", "mile-per-hour");

    /**
     * Constant for unit of temperature: celsius
     * @stable ICU 53
     */
    public static final MeasureUnit CELSIUS = MeasureUnit.internalGetInstance("temperature", "celsius");

    /**
     * Constant for unit of temperature: fahrenheit
     * @stable ICU 53
     */
    public static final MeasureUnit FAHRENHEIT = MeasureUnit.internalGetInstance("temperature", "fahrenheit");

    /**
     * Constant for unit of temperature: generic
     * @stable ICU 56
     */
    public static final MeasureUnit GENERIC_TEMPERATURE = MeasureUnit.internalGetInstance("temperature", "generic");

    /**
     * Constant for unit of temperature: kelvin
     * @stable ICU 54
     */
    public static final MeasureUnit KELVIN = MeasureUnit.internalGetInstance("temperature", "kelvin");

    /**
     * Constant for unit of torque: newton-meter
     * @stable ICU 64
     */
    public static final MeasureUnit NEWTON_METER = MeasureUnit.internalGetInstance("torque", "newton-meter");

    /**
     * Constant for unit of torque: pound-force-foot
     * @stable ICU 64
     */
    public static final MeasureUnit POUND_FOOT = MeasureUnit.internalGetInstance("torque", "pound-force-foot");

    /**
     * Constant for unit of volume: acre-foot
     * @stable ICU 54
     */
    public static final MeasureUnit ACRE_FOOT = MeasureUnit.internalGetInstance("volume", "acre-foot");

    /**
     * Constant for unit of volume: barrel
     * @stable ICU 64
     */
    public static final MeasureUnit BARREL = MeasureUnit.internalGetInstance("volume", "barrel");

    /**
     * Constant for unit of volume: bushel
     * @stable ICU 54
     */
    public static final MeasureUnit BUSHEL = MeasureUnit.internalGetInstance("volume", "bushel");

    /**
     * Constant for unit of volume: centiliter
     * @stable ICU 54
     */
    public static final MeasureUnit CENTILITER = MeasureUnit.internalGetInstance("volume", "centiliter");

    /**
     * Constant for unit of volume: cubic-centimeter
     * @stable ICU 54
     */
    public static final MeasureUnit CUBIC_CENTIMETER = MeasureUnit.internalGetInstance("volume", "cubic-centimeter");

    /**
     * Constant for unit of volume: cubic-foot
     * @stable ICU 54
     */
    public static final MeasureUnit CUBIC_FOOT = MeasureUnit.internalGetInstance("volume", "cubic-foot");

    /**
     * Constant for unit of volume: cubic-inch
     * @stable ICU 54
     */
    public static final MeasureUnit CUBIC_INCH = MeasureUnit.internalGetInstance("volume", "cubic-inch");

    /**
     * Constant for unit of volume: cubic-kilometer
     * @stable ICU 53
     */
    public static final MeasureUnit CUBIC_KILOMETER = MeasureUnit.internalGetInstance("volume", "cubic-kilometer");

    /**
     * Constant for unit of volume: cubic-meter
     * @stable ICU 54
     */
    public static final MeasureUnit CUBIC_METER = MeasureUnit.internalGetInstance("volume", "cubic-meter");

    /**
     * Constant for unit of volume: cubic-mile
     * @stable ICU 53
     */
    public static final MeasureUnit CUBIC_MILE = MeasureUnit.internalGetInstance("volume", "cubic-mile");

    /**
     * Constant for unit of volume: cubic-yard
     * @stable ICU 54
     */
    public static final MeasureUnit CUBIC_YARD = MeasureUnit.internalGetInstance("volume", "cubic-yard");

    /**
     * Constant for unit of volume: cup
     * @stable ICU 54
     */
    public static final MeasureUnit CUP = MeasureUnit.internalGetInstance("volume", "cup");

    /**
     * Constant for unit of volume: cup-metric
     * @stable ICU 56
     */
    public static final MeasureUnit CUP_METRIC = MeasureUnit.internalGetInstance("volume", "cup-metric");

    /**
     * Constant for unit of volume: deciliter
     * @stable ICU 54
     */
    public static final MeasureUnit DECILITER = MeasureUnit.internalGetInstance("volume", "deciliter");

    /**
     * Constant for unit of volume: dessert-spoon
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
    */
    public static final MeasureUnit DESSERT_SPOON = MeasureUnit.internalGetInstance("volume", "dessert-spoon");

    /**
     * Constant for unit of volume: dessert-spoon-imperial
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
    */
    public static final MeasureUnit DESSERT_SPOON_IMPERIAL = MeasureUnit.internalGetInstance("volume", "dessert-spoon-imperial");

    /**
     * Constant for unit of volume: dram
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
    */
    public static final MeasureUnit DRAM = MeasureUnit.internalGetInstance("volume", "dram");

    /**
     * Constant for unit of volume: drop
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
    */
    public static final MeasureUnit DROP = MeasureUnit.internalGetInstance("volume", "drop");

    /**
     * Constant for unit of volume: fluid-ounce
     * @stable ICU 54
     */
    public static final MeasureUnit FLUID_OUNCE = MeasureUnit.internalGetInstance("volume", "fluid-ounce");

    /**
     * Constant for unit of volume: fluid-ounce-imperial
     * @stable ICU 64
     */
    public static final MeasureUnit FLUID_OUNCE_IMPERIAL = MeasureUnit.internalGetInstance("volume", "fluid-ounce-imperial");

    /**
     * Constant for unit of volume: gallon
     * @stable ICU 54
     */
    public static final MeasureUnit GALLON = MeasureUnit.internalGetInstance("volume", "gallon");

    /**
     * Constant for unit of volume: gallon-imperial
     * @stable ICU 57
     */
    public static final MeasureUnit GALLON_IMPERIAL = MeasureUnit.internalGetInstance("volume", "gallon-imperial");

    /**
     * Constant for unit of volume: hectoliter
     * @stable ICU 54
     */
    public static final MeasureUnit HECTOLITER = MeasureUnit.internalGetInstance("volume", "hectoliter");

    /**
     * Constant for unit of volume: jigger
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
    */
    public static final MeasureUnit JIGGER = MeasureUnit.internalGetInstance("volume", "jigger");

    /**
     * Constant for unit of volume: liter
     * @stable ICU 53
     */
    public static final MeasureUnit LITER = MeasureUnit.internalGetInstance("volume", "liter");

    /**
     * Constant for unit of volume: megaliter
     * @stable ICU 54
     */
    public static final MeasureUnit MEGALITER = MeasureUnit.internalGetInstance("volume", "megaliter");

    /**
     * Constant for unit of volume: milliliter
     * @stable ICU 54
     */
    public static final MeasureUnit MILLILITER = MeasureUnit.internalGetInstance("volume", "milliliter");

    /**
     * Constant for unit of volume: pinch
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
    */
    public static final MeasureUnit PINCH = MeasureUnit.internalGetInstance("volume", "pinch");

    /**
     * Constant for unit of volume: pint
     * @stable ICU 54
     */
    public static final MeasureUnit PINT = MeasureUnit.internalGetInstance("volume", "pint");

    /**
     * Constant for unit of volume: pint-metric
     * @stable ICU 56
     */
    public static final MeasureUnit PINT_METRIC = MeasureUnit.internalGetInstance("volume", "pint-metric");

    /**
     * Constant for unit of volume: quart
     * @stable ICU 54
     */
    public static final MeasureUnit QUART = MeasureUnit.internalGetInstance("volume", "quart");

    /**
     * Constant for unit of volume: quart-imperial
     * @draft ICU 68
     * @provisional This API might change or be removed in a future release.
    */
    public static final MeasureUnit QUART_IMPERIAL = MeasureUnit.internalGetInstance("volume", "quart-imperial");

    /**
     * Constant for unit of volume: tablespoon
     * @stable ICU 54
     */
    public static final MeasureUnit TABLESPOON = MeasureUnit.internalGetInstance("volume", "tablespoon");

    /**
     * Constant for unit of volume: teaspoon
     * @stable ICU 54
     */
    public static final MeasureUnit TEASPOON = MeasureUnit.internalGetInstance("volume", "teaspoon");

    // unitPerUnitToSingleUnit no longer in use! TODO: remove from code-generation code.

    // End generated MeasureUnit constants
    /* Private */

    private Object writeReplace() throws ObjectStreamException {
        return new MeasureUnitProxy(type, subType);
    }

    /**
     *
     * @return this object as a SingleUnitImpl.
     * @throws UnsupportedOperationException if this object could not be converted to a single unit.
     */
    private SingleUnitImpl getSingleUnitImpl() {
        if (measureUnitImpl == null) {
            return MeasureUnitImpl.forIdentifier(getIdentifier()).getSingleUnitImpl();
        }

        return measureUnitImpl.getSingleUnitImpl();
    }

    /**
     *
     * @return this object in a MeasureUnitImpl form.
     */
    private MeasureUnitImpl getCopyOfMeasureUnitImpl() {
        return this.measureUnitImpl == null ?
                MeasureUnitImpl.forIdentifier(getIdentifier()) :
                this.measureUnitImpl.copy();
    }

    /**
     *
     * @return this object in a MeasureUnitImpl form.
     */
    private MeasureUnitImpl getMayBeReferenceOfMeasureUnitImpl(){
        return this.measureUnitImpl == null ?
                MeasureUnitImpl.forIdentifier(getIdentifier()) :
                this.measureUnitImpl;
    }

    static final class MeasureUnitProxy implements Externalizable {
        private static final long serialVersionUID = -3910681415330989598L;

        private String type;
        private String subType;

        public MeasureUnitProxy(String type, String subType) {
            this.type = type;
            this.subType = subType;
        }

        // Must have public constructor, to enable Externalizable
        public MeasureUnitProxy() {
        }

        @Override
        public void writeExternal(ObjectOutput out) throws IOException {
            out.writeByte(0); // version
            out.writeUTF(type);
            out.writeUTF(subType);
            out.writeShort(0); // allow for more data.
        }

        @Override
        public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
            /* byte version = */ in.readByte(); // version
            type = in.readUTF();
            subType = in.readUTF();
            // allow for more data from future version
            int extra = in.readShort();
            if (extra > 0) {
                byte[] extraBytes = new byte[extra];
                in.read(extraBytes, 0, extra);
            }
        }

        private Object readResolve() throws ObjectStreamException {
            return MeasureUnit.internalGetInstance(type, subType);
        }
    }
}