ICU-22781 Support Arbitrary Constant Unit Formatting (Java)

- Added support for constant denominators in MeasureUnit and LongNameHandler
- Implemented test cases for formatting units with arbitrary constant denominators
- Updated MeasureUnit serialization and product methods to handle constant denominators
- Added comprehensive test coverage for complex unit formatting scenarios

icu4j/main/common_tests/src/test/java/com/ibm/icu/dev/test/format/NumberFormatTest.java

@@ -51,6 +51,9 @@
 import com.ibm.icu.impl.number.PatternStringUtils;
 import com.ibm.icu.math.BigDecimal;
 import com.ibm.icu.math.MathContext;
+import com.ibm.icu.number.LocalizedNumberFormatter;
+import com.ibm.icu.number.NumberFormatter;
+import com.ibm.icu.number.NumberFormatter.UnitWidth;
 import com.ibm.icu.text.CompactDecimalFormat;
 import com.ibm.icu.text.CurrencyPluralInfo;
 import com.ibm.icu.text.DecimalFormat;
@@ -66,6 +69,7 @@
 import com.ibm.icu.util.Currency;
 import com.ibm.icu.util.Currency.CurrencyUsage;
 import com.ibm.icu.util.CurrencyAmount;
+import com.ibm.icu.util.MeasureUnit;
 import com.ibm.icu.util.ULocale;
 
 @RunWith(JUnit4.class)
@@ -7056,4 +7060,64 @@ public void TestParseWithEmptyCurr() {
 
         }
     }
+
+    @Test
+    public void TestArbitraryConstantFormatting() {
+
+        class TestData {
+            String unitIdentifier;
+            Integer inputValue;
+            String expectedOutput;
+            UnitWidth width;
+            ULocale locale;
+
+            public TestData(String unitIdentifier, Integer inputValue, UnitWidth width, ULocale locale,
+                    String expectedOutput) {
+                this.unitIdentifier = unitIdentifier;
+                this.inputValue = inputValue;
+                this.expectedOutput = expectedOutput;
+                this.width = width;
+                this.locale = locale;
+            }
+        }
+
+        TestData[] testData = {
+                new TestData("meter-per-kelvin-second", 2, UnitWidth.FULL_NAME, ULocale.ENGLISH,
+                        "2 meters per second-kelvin"),
+                new TestData("meter-per-100-kelvin-second", 3, UnitWidth.FULL_NAME, ULocale.ENGLISH,
+                        "3 meters per 100-second-kelvin"),
+                new TestData("meter-per-kelvin-second", 1, UnitWidth.FULL_NAME, ULocale.ENGLISH,
+                        "1 meter per second-kelvin"),
+                new TestData("meter-per-1000", 1, UnitWidth.FULL_NAME, ULocale.ENGLISH, "1 meter per 1000"),
+                new TestData("meter-per-1000-second", 1, UnitWidth.FULL_NAME, ULocale.ENGLISH,
+                        "1 meter per 1000-second"),
+                new TestData("meter-per-1000-second-kelvin", 1, UnitWidth.FULL_NAME, ULocale.ENGLISH,
+                        "1 meter per 1000-second-kelvin"),
+                new TestData("meter-per-1-second-kelvin-per-kilogram", 1, UnitWidth.FULL_NAME, ULocale.ENGLISH,
+                        "1 meter per 1-kilogram-second-kelvin"),
+                new TestData("meter-second-per-kilogram-kelvin", 1, UnitWidth.FULL_NAME, ULocale.ENGLISH,
+                        "1 meter-second per kilogram-kelvin"),
+                new TestData("meter-second-per-1000-kilogram-kelvin", 1, UnitWidth.FULL_NAME, ULocale.ENGLISH,
+                        "1 meter-second per 1000-kilogram-kelvin"),
+                new TestData("meter-second-per-1000-kilogram-kelvin", 1, UnitWidth.SHORT, ULocale.ENGLISH,
+                        "1 m⋅sec/1000⋅kg⋅K"),
+                new TestData("meter-second-per-1000-kilogram-kelvin", 1, UnitWidth.FULL_NAME, ULocale.GERMAN,
+                        "1 Meter⋅Sekunde pro 1000⋅Kilogramm⋅Kelvin"),
+                new TestData("meter-second-per-1000-kilogram-kelvin", 1, UnitWidth.SHORT, ULocale.GERMAN,
+                        "1 m⋅Sek./1000⋅kg⋅K"),
+        };
+
+        for (TestData testCase : testData) {
+            MeasureUnit unit = MeasureUnit.forIdentifier(testCase.unitIdentifier);
+            LocalizedNumberFormatter formatter = NumberFormatter.withLocale(testCase.locale).unit(unit)
+                    .unitWidth(testCase.width);
+
+            String formatted = formatter.format(testCase.inputValue).toString();
+            assertEquals(
+                    "Unit: " + testCase.unitIdentifier + ", Width: " + testCase.width + ", Input: "
+                            + testCase.inputValue,
+                    testCase.expectedOutput, formatted);
+        }
+
+    }
 }

icu4j/main/core/src/main/java/com/ibm/icu/impl/number/LongNameHandler.java

@@ -40,6 +40,7 @@ public class LongNameHandler
     private static final int DNAM_INDEX = StandardPlural.COUNT + i++;
     private static final int PER_INDEX = StandardPlural.COUNT + i++;
     private static final int GENDER_INDEX = StandardPlural.COUNT + i++;
+    private static final int CONSTANT_DENOMINATOR_INDEX = StandardPlural.COUNT + i++;
     static final int ARRAY_LENGTH = StandardPlural.COUNT + i++;
 
     // Returns the array index that corresponds to the given pluralKeyword.
@@ -860,6 +861,13 @@ private static LongNameHandler forArbitraryUnit(ULocale loc,
         MeasureUnitImpl fullUnit = unit.getCopyOfMeasureUnitImpl();
         unit = null;
         MeasureUnit perUnit = null;
+
+        if (fullUnit.getConstantDenominator() != 0) {
+            MeasureUnitImpl perUnitImpl = new MeasureUnitImpl();
+            perUnitImpl.setConstantDenominator(fullUnit.getConstantDenominator());
+            perUnit = perUnitImpl.build();
+        }
+
         // TODO(icu-units#28): lots of inefficiency in the handling of
         // MeasureUnit/MeasureUnitImpl:
         for (SingleUnitImpl subUnit : fullUnit.getSingleUnits()) {
@@ -1053,7 +1061,7 @@ private static void processPatternTimes(MeasureUnitImpl productUnit,
             // TODO(icu-units#28): ensure we have unit tests that change/fail if we
             // assign incorrect case variants here:
             if (singleUnitIndex < singleUnits.size() - 1) {
-                // 4.1. If hasMultiple
+                // 4.1. If hasMultipleUnits is true
                 singlePluralCategory = derivedTimesPlurals.value0(pluralCategory);
                 singleCaseVariant = derivedTimesCases.value0(caseVariant);
                 pluralCategory = derivedTimesPlurals.value1(pluralCategory);
@@ -1116,7 +1124,7 @@ private static void processPatternTimes(MeasureUnitImpl productUnit,
             String prefixPattern = "";
             if (prefix != MeasurePrefix.ONE) {
                 // 4.4.1. set siPrefixPattern to be getValue(that si_prefix, locale,
-                //        length), such as "centy{0}"
+                // length), such as "centy{0}"
                 StringBuilder prefixKey = new StringBuilder();
                 // prefixKey looks like "1024p3" or "10p-2":
                 prefixKey.append(prefix.getBase());
@@ -1143,7 +1151,7 @@ private static void processPatternTimes(MeasureUnitImpl productUnit,
             }
 
             // 4.5. Set corePattern to be the getValue(singleUnit, locale, length,
-            //      singlePluralCategory, singleCaseVariant), such as "{0} metrem"
+            // singlePluralCategory, singleCaseVariant), such as "{0} metrem"
             String[] singleUnitArray = new String[ARRAY_LENGTH];
             // At this point we are left with a Simple Unit:
             assert singleUnit.build().getIdentifier().equals(singleUnit.getSimpleUnitID())
@@ -1238,8 +1246,9 @@ private static void processPatternTimes(MeasureUnitImpl productUnit,
                     String prefixCompiled =
                         SimpleFormatterImpl.compileToStringMinMaxArguments(prefixPattern, sb, 1, 1);
 
-                    // 4.9.1. Set coreUnit to be the combineLowercasing(locale, length, siPrefixPattern,
-                    //        coreUnit)
+                    // 4.9.1. Set coreUnit to be the combineLowercasing(locale, length,
+                    // siPrefixPattern,
+                    // coreUnit)
                     // combineLowercasing(locale, length, prefixPattern, coreUnit)
                     //
                     // TODO(icu-units#28): run this only if prefixPattern does not
@@ -1257,7 +1266,7 @@ private static void processPatternTimes(MeasureUnitImpl productUnit,
                         getWithPlural(dimensionalityPrefixPatterns, plural), sb, 1, 1);
 
                     // 4.10.1. Set coreUnit to be the combineLowercasing(locale, length,
-                    //         dimensionalityPrefixPattern, coreUnit)
+                    // dimensionalityPrefixPattern, coreUnit)
                     // combineLowercasing(locale, length, prefixPattern, coreUnit)
                     //
                     // TODO(icu-units#28): run this only if prefixPattern does not
@@ -1280,6 +1289,39 @@ private static void processPatternTimes(MeasureUnitImpl productUnit,
                 }
             }
         }
+
+        // 5. Handling constant denominator if it exists.
+        if (productUnit.getConstantDenominator() != 0) {
+            outArray[CONSTANT_DENOMINATOR_INDEX] = String.valueOf(productUnit.getConstantDenominator());
+            Integer pluralIndex = null;
+            for (StandardPlural plural_ : StandardPlural.values()) {
+                if (outArray[plural_.ordinal()] != null) {
+                    pluralIndex = plural_.ordinal();
+                    break;
+                }
+            }
+
+            assert pluralIndex != null : "No plural form found for constant denominator";
+
+            // TODO(ICU-23039):
+            // Improve the handling of constant_denominator representation.
+            // For instance, a constant_denominator of 1000000 should be adaptable to
+            // formats like
+            // 1,000,000, 1e6, or 1 million.
+            // Furthermore, ensure consistent pluralization rules for units. For example,
+            // "meter per 100 seconds" should be evaluated for correct singular/plural
+            // usage: "second" or "seconds"?
+            // Similarly, "kilogram per 1000 meters" should be checked for "meter" or
+            // "meters"?
+            if (outArray[pluralIndex].length() == 0) {
+                outArray[pluralIndex] = outArray[CONSTANT_DENOMINATOR_INDEX];
+            } else {
+                outArray[pluralIndex] = SimpleFormatterImpl.formatCompiledPattern(
+                        timesPatternFormatter, outArray[CONSTANT_DENOMINATOR_INDEX], outArray[pluralIndex]);
+            }
+
+        }
+
         for (StandardPlural plural : StandardPlural.values()) {
             int pluralIndex = plural.ordinal();
             if (globalPlaceholder[pluralIndex] == PlaceholderPosition.BEGINNING) {

icu4j/main/core/src/main/java/com/ibm/icu/impl/units/MeasureUnitImpl.java

@@ -300,7 +300,7 @@ private String getConstantsString(long constantDenominator) {
      * Normalizes the MeasureUnitImpl and generates the identifier string in place.
      */
     public void serialize() {
-        if (this.getSingleUnits().size() == 0) {
+        if (this.getSingleUnits().size() == 0 && this.constantDenominator == 0) {
             // Dimensionless, constructed by the default constructor: no appending
             // to this.result, we wish it to contain the zero-length string.
             return;

icu4j/main/core/src/main/java/com/ibm/icu/util/MeasureUnit.java

@@ -716,6 +716,13 @@ public MeasureUnit product(MeasureUnit other) {
             implCopy.appendSingleUnit(singleUnit);
         }
 
+        if (this.getConstantDenominator() != 0 && other.getConstantDenominator() != 0) {
+            throw new UnsupportedOperationException(
+                    "Cannot multiply units that both of them have a constant denominator");
+        }
+
+        implCopy.setConstantDenominator(this.getConstantDenominator() + other.getConstantDenominator());
+
         return implCopy.build();
     }