ICU-22872 Fix BigDecimal scale in DecimalFormat.parse()

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

@@ -8677,4 +8677,42 @@ public void testStrictParse() throws java.text.ParseException {
             }
         }
     }
+
+    /**
+     * Test that BigDecimal scale is correctly preserved when parsing numbers with trailing zeros.
+     * This is a regression test for ICU-22872.
+     */
+    @Test
+    public void TestParseBigDecimalScale() throws ParseException {
+        DecimalFormat df = new DecimalFormat("0.00");
+        df.setParseBigDecimal(true);
+
+        // Test cases: input string, expected scale
+        Object[][] testCases = {
+            {"0.0", 1},
+            {"1.0", 1},
+            {"1.00", 2},
+            {"1.10", 2},
+            {"0.10", 2},
+            {"123.450", 3},
+            {"5.0000", 4},
+        };
+
+        for (Object[] testCase : testCases) {
+            String input = (String) testCase[0];
+            int expectedScale = (Integer) testCase[1];
+            Number result = df.parse(input);
+            assertTrue("Result should be BigDecimal for input: " + input, result instanceof BigDecimal);
+            BigDecimal bd = (BigDecimal) result;
+            assertEquals("Scale mismatch for input: " + input, expectedScale, bd.scale());
+        }
+
+        // Verify values are correct, not just scales
+        assertEquals("Value check for 0.0",
+                new BigDecimal("0.0"), df.parse("0.0"));
+        assertEquals("Value check for 1.00",
+                new BigDecimal("1.00"), df.parse("1.00"));
+        assertEquals("Value check for 123.450",
+                new BigDecimal("123.450"), df.parse("123.450"));
+    }
 }

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

@@ -432,6 +432,7 @@ public boolean match(StringSegment segment, ParsedNumber result, int exponentSig
         // Set other information into the result and return.
         if (actualDecimalString != null) {
             result.flags |= ParsedNumber.FLAG_HAS_DECIMAL_SEPARATOR;
+            result.fractionDigitCount = digitsAfterDecimalPlace;
         }
         result.setCharsConsumed(segment);
         return segment.length() == 0 || maybeMore;

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

@@ -36,6 +36,13 @@ public class ParsedNumber {
     /** The currency that got consumed. */
     public String currencyCode;
 
+    /** 
+     * The number of digits after the decimal separator, including trailing zeros.
+     * Used to preserve scale when parsing BigDecimals.
+     * A value of -1 means no decimal separator was seen.
+     */
+    public int fractionDigitCount;
+
     public static final int FLAG_NEGATIVE = 0x0001;
     public static final int FLAG_PERCENT = 0x0002;
     public static final int FLAG_PERMILLE = 0x0004;
@@ -67,6 +74,7 @@ public void clear() {
         prefix = null;
         suffix = null;
         currencyCode = null;
+        fractionDigitCount = -1;
     }
 
     public void copyFrom(ParsedNumber other) {
@@ -79,6 +87,7 @@ public void copyFrom(ParsedNumber other) {
         prefix = other.prefix;
         suffix = other.suffix;
         currencyCode = other.currencyCode;
+        fractionDigitCount = other.fractionDigitCount;
     }
 
     /**
@@ -128,6 +137,7 @@ public Number getNumber() {
     public Number getNumber(int parseFlags) {
         boolean sawNaN = 0 != (flags & FLAG_NAN);
         boolean sawInfinity = 0 != (flags & FLAG_INFINITY);
+        boolean sawExponent = 0 != (flags & FLAG_HAS_EXPONENT);
         boolean forceBigDecimal = 0 != (parseFlags & ParsingUtils.PARSE_FLAG_FORCE_BIG_DECIMAL);
         boolean integerOnly = 0 != (parseFlags & ParsingUtils.PARSE_FLAG_INTEGER_ONLY);
 
@@ -150,7 +160,13 @@ public Number getNumber(int parseFlags) {
         if (quantity.fitsInLong() && !forceBigDecimal) {
             return quantity.toLong(false);
         } else {
-            return quantity.toBigDecimal();
+            java.math.BigDecimal result = quantity.toBigDecimal();
+            // Preserve trailing zeros by adjusting scale based on fractionDigitCount
+            // Only do this when no exponent was seen (exponent changes the scale)
+            if (!sawExponent && fractionDigitCount >= 0 && result.scale() < fractionDigitCount) {
+                result = result.setScale(fractionDigitCount);
+            }
+            return result;
         }
     }