Cherry-pick: ICU-22226 Fix Calendar.getFirstDayOfWeek to honor -u-fw

Upstream commit:
https://github.com/unicode-org/icu/commit/76df897b77fd938abc29c9121dde794300a171e6

Upstream bug:
https://unicode-org.atlassian.net/browse/ICU-11870

Test: m droid
Change-Id: Ic48e20ac9f94eea6246eb37e19b294c375262afe

2 files changed, 51 insertions, 0 deletions

diff --git a/icu4j/main/classes/core/src/com/ibm/icu/util/Calendar.java b/icu4j/main/classes/core/src/com/ibm/icu/util/Calendar.java
index 1441950cc..878f558cb 100644
--- a/icu4j/main/classes/core/src/com/ibm/icu/util/Calendar.java
+++ b/icu4j/main/classes/core/src/com/ibm/icu/util/Calendar.java
@@ -1595,6 +1595,25 @@ public abstract class Calendar implements Serializable, Cloneable, Comparable<Ca
         // week data
         setWeekData(getRegionForCalendar(locale));
 
+        // Check if the locale has a "fw" u extension and we honor it if present.
+        String fw = locale.getKeywordValue("fw");
+        if (fw != null) {
+            int fwOverride;
+            switch (fw) {
+                case "sun": fwOverride = SUNDAY; break;
+                case "mon": fwOverride = MONDAY; break;
+                case "tue": fwOverride = TUESDAY; break;
+                case "wed": fwOverride = WEDNESDAY; break;
+                case "thu": fwOverride = THURSDAY; break;
+                case "fri": fwOverride = FRIDAY; break;
+                case "sat": fwOverride = SATURDAY; break;
+                default: fwOverride = -1;
+            }
+            if (fwOverride != -1) {
+                setFirstDayOfWeek(fwOverride);
+            }
+        }
+
         // set valid/actual locale
         setCalendarLocale(locale);
 
diff --git a/icu4j/main/tests/core/src/com/ibm/icu/dev/test/calendar/CalendarRegressionTest.java b/icu4j/main/tests/core/src/com/ibm/icu/dev/test/calendar/CalendarRegressionTest.java
index 717141fb6..7931d70cf 100644
--- a/icu4j/main/tests/core/src/com/ibm/icu/dev/test/calendar/CalendarRegressionTest.java
+++ b/icu4j/main/tests/core/src/com/ibm/icu/dev/test/calendar/CalendarRegressionTest.java
@@ -2623,5 +2623,37 @@ public class CalendarRegressionTest extends com.ibm.icu.dev.test.TestFmwk {
                          TESTS[i][2], cal.getType());
         }
     }
+
+    @Test
+    public void TestRespectUExtensionFw() { // ICU-22226
+        String[] localeIds = {
+                "en-US",
+                "en-US-u-fw-xyz",
+                "en-US-u-fw-sun",
+                "en-US-u-fw-mon",
+                "en-US-u-fw-thu",
+                "en-US-u-fw-sat"
+        };
+        int[] expectedValues = {
+                Calendar.SUNDAY,
+                Calendar.SUNDAY,
+                Calendar.SUNDAY,
+                Calendar.MONDAY,
+                Calendar.THURSDAY,
+                Calendar.SATURDAY
+        };
+
+        assertEquals(
+                "The localeIds count matches the expectedValues count",
+                localeIds.length,
+                expectedValues.length);
+
+        for (int i = 0; i < localeIds.length; i++) {
+            assertEquals(
+                    "Calendar.getFirstDayOfWeek() does not seem to respect fw extension u in locale id",
+                    expectedValues[i],
+                    Calendar.getInstance(Locale.forLanguageTag(localeIds[i])).getFirstDayOfWeek());
+        }
+    }
 }
 //eof