diff --git a/src/java.base/share/classes/sun/util/calendar/AbstractCalendar.java b/src/java.base/share/classes/sun/util/calendar/AbstractCalendar.java
index 50c8be6e314..f2582b80e47 100644
--- a/src/java.base/share/classes/sun/util/calendar/AbstractCalendar.java
+++ b/src/java.base/share/classes/sun/util/calendar/AbstractCalendar.java
@@ -44,7 +44,8 @@ import java.util.TimeZone;
  * @since 1.5
  */
 
-public abstract class AbstractCalendar extends CalendarSystem {
+public sealed abstract class AbstractCalendar extends CalendarSystem
+        permits BaseCalendar {
 
     // The constants assume no leap seconds support.
     static final int SECOND_IN_MILLIS = 1000;
@@ -60,6 +61,7 @@ public abstract class AbstractCalendar extends CalendarSystem {
     protected AbstractCalendar() {
     }
 
+    @Override
     public Era getEra(String eraName) {
         if (eras != null) {
             for (Era era : eras) {
@@ -71,6 +73,7 @@ public abstract class AbstractCalendar extends CalendarSystem {
         return null;
     }
 
+    @Override
     public Era[] getEras() {
         Era[] e = null;
         if (eras != null) {
@@ -84,19 +87,23 @@ public abstract class AbstractCalendar extends CalendarSystem {
         this.eras = eras;
     }
 
+    @Override
     public CalendarDate getCalendarDate() {
         return getCalendarDate(System.currentTimeMillis(), newCalendarDate());
     }
 
+    @Override
     public CalendarDate getCalendarDate(long millis) {
         return getCalendarDate(millis, newCalendarDate());
     }
 
+    @Override
     public CalendarDate getCalendarDate(long millis, TimeZone zone) {
         CalendarDate date = newCalendarDate(zone);
         return getCalendarDate(millis, date);
     }
 
+    @Override
     public CalendarDate getCalendarDate(long millis, CalendarDate date) {
         int ms = 0;             // time of day
         int zoneOffset = 0;
@@ -156,6 +163,7 @@ public abstract class AbstractCalendar extends CalendarSystem {
         return date;
     }
 
+    @Override
     public long getTime(CalendarDate date) {
         long gd = getFixedDate(date);
         long ms = (gd - EPOCH_OFFSET) * DAY_IN_MILLIS + getTimeOfDay(date);
@@ -232,6 +240,7 @@ public abstract class AbstractCalendar extends CalendarSystem {
 
     protected abstract boolean isLeapYear(CalendarDate date);
 
+    @Override
     public CalendarDate getNthDayOfWeek(int nth, int dayOfWeek, CalendarDate date) {
         CalendarDate ndate = (CalendarDate) date.clone();
         normalize(ndate);
diff --git a/src/java.base/share/classes/sun/util/calendar/BaseCalendar.java b/src/java.base/share/classes/sun/util/calendar/BaseCalendar.java
index efe1b85fc21..9749ab31afd 100644
--- a/src/java.base/share/classes/sun/util/calendar/BaseCalendar.java
+++ b/src/java.base/share/classes/sun/util/calendar/BaseCalendar.java
@@ -36,7 +36,8 @@ import java.util.TimeZone;
  * @since 1.5
  */
 
-public abstract class BaseCalendar extends AbstractCalendar {
+public sealed abstract class BaseCalendar extends AbstractCalendar
+        permits Gregorian, JulianCalendar, LocalGregorianCalendar {
 
     public static final int JANUARY = 1;
     public static final int FEBRUARY = 2;
@@ -140,7 +141,8 @@ public abstract class BaseCalendar extends AbstractCalendar {
         744365, // 2039
     };
 
-    public abstract static class Date extends CalendarDate {
+    public sealed abstract static class Date extends CalendarDate
+            permits Gregorian.Date, ImmutableGregorianDate, JulianCalendar.Date, LocalGregorianCalendar.Date {
         protected Date() {
             super();
         }
@@ -188,6 +190,7 @@ public abstract class BaseCalendar extends AbstractCalendar {
         }
     }
 
+    @Override
     public boolean validate(CalendarDate date) {
         Date bdate = (Date) date;
         if (bdate.isNormalized()) {
@@ -214,6 +217,7 @@ public abstract class BaseCalendar extends AbstractCalendar {
         return true;
     }
 
+    @Override
     public boolean normalize(CalendarDate date) {
         if (date.isNormalized()) {
             return true;
@@ -303,6 +307,7 @@ public abstract class BaseCalendar extends AbstractCalendar {
      * @throws ClassCastException if the specified date is not a
      * {@link BaseCalendar.Date}
      */
+    @Override
     public int getYearLength(CalendarDate date) {
         return isLeapYear(((Date)date).getNormalizedYear()) ? 366 : 365;
     }
@@ -318,6 +323,7 @@ public abstract class BaseCalendar extends AbstractCalendar {
         //  12/1 1/1 2/1   3/1   4/1   5/1   6/1   7/1   8/1   9/1   10/1   11/1   12/1
         = {  -30,  0, 31, 59+1, 90+1,120+1,151+1,181+1,212+1,243+1, 273+1, 304+1, 334+1};
 
+    @Override
     public int getMonthLength(CalendarDate date) {
         Date gdate = (Date) date;
         int month = gdate.getMonth();
@@ -349,6 +355,7 @@ public abstract class BaseCalendar extends AbstractCalendar {
     }
 
     // protected
+    @Override
     public long getFixedDate(CalendarDate date) {
         if (!date.isNormalized()) {
             normalizeMonth(date);
@@ -415,6 +422,7 @@ public abstract class BaseCalendar extends AbstractCalendar {
      * {@code CalendarDate}.
      */
     // should be 'protected'
+    @Override
     public void getCalendarDateFromFixedDate(CalendarDate date,
                                              long fixedDate) {
         Date gdate = (Date) date;
@@ -473,7 +481,7 @@ public abstract class BaseCalendar extends AbstractCalendar {
         return getDayOfWeekFromFixedDate(fixedDate);
     }
 
-    public static final int getDayOfWeekFromFixedDate(long fixedDate) {
+    public static int getDayOfWeekFromFixedDate(long fixedDate) {
         // The fixed day 1 (January 1, 1 Gregorian) is Monday.
         if (fixedDate >= 0) {
             return (int)(fixedDate % 7) + SUNDAY;
@@ -525,6 +533,7 @@ public abstract class BaseCalendar extends AbstractCalendar {
      * false otherwise.
      * @see CalendarUtils#isGregorianLeapYear
      */
+    @Override
     protected boolean isLeapYear(CalendarDate date) {
         return isLeapYear(((Date)date).getNormalizedYear());
     }
diff --git a/src/java.base/share/classes/sun/util/calendar/CalendarDate.java b/src/java.base/share/classes/sun/util/calendar/CalendarDate.java
index 528baa9e317..7485a9fb37a 100644
--- a/src/java.base/share/classes/sun/util/calendar/CalendarDate.java
+++ b/src/java.base/share/classes/sun/util/calendar/CalendarDate.java
@@ -59,7 +59,8 @@ import java.util.TimeZone;
  * @author Masayoshi Okutsu
  * @since 1.5
  */
-public abstract class CalendarDate implements Cloneable {
+public sealed abstract class CalendarDate implements Cloneable
+        permits BaseCalendar.Date {
     public static final int FIELD_UNDEFINED = Integer.MIN_VALUE;
     public static final long TIME_UNDEFINED = Long.MIN_VALUE;
 
@@ -340,6 +341,7 @@ public abstract class CalendarDate implements Cloneable {
                 && zoneOffset == that.zoneOffset);
     }
 
+    @Override
     public int hashCode() {
         // a pseudo (local standard) time stamp value in milliseconds
         // from the Epoch, assuming Gregorian calendar fields.
@@ -362,6 +364,7 @@ public abstract class CalendarDate implements Cloneable {
      *
      * @return a copy of this <code>CalendarDate</code>
      */
+    @Override
     public Object clone() {
         try {
             return super.clone();
@@ -380,6 +383,7 @@ public abstract class CalendarDate implements Cloneable {
      *
      * @see java.text.SimpleDateFormat
      */
+    @Override
     public String toString() {
         StringBuilder sb = new StringBuilder();
         CalendarUtils.sprintf0d(sb, year, 4).append('-');
diff --git a/src/java.base/share/classes/sun/util/calendar/CalendarSystem.java b/src/java.base/share/classes/sun/util/calendar/CalendarSystem.java
index 885150fc0a4..ea4f76c5bf0 100644
--- a/src/java.base/share/classes/sun/util/calendar/CalendarSystem.java
+++ b/src/java.base/share/classes/sun/util/calendar/CalendarSystem.java
@@ -65,7 +65,7 @@ import java.util.concurrent.ConcurrentMap;
  * @since 1.5
  */
 
-public abstract class CalendarSystem {
+public sealed abstract class CalendarSystem permits AbstractCalendar {
 
     /////////////////////// Calendar Factory Methods /////////////////////////
 
diff --git a/src/java.base/share/classes/sun/util/calendar/CalendarUtils.java b/src/java.base/share/classes/sun/util/calendar/CalendarUtils.java
index 5723ebcbee0..60c2decc48b 100644
--- a/src/java.base/share/classes/sun/util/calendar/CalendarUtils.java
+++ b/src/java.base/share/classes/sun/util/calendar/CalendarUtils.java
@@ -25,7 +25,10 @@
 
 package sun.util.calendar;
 
-public class CalendarUtils {
+public final class CalendarUtils {
+
+    // Utility class should not be instantiated
+    private CalendarUtils() {}
 
     /**
      * Returns whether the specified year is a leap year in the Gregorian
@@ -36,9 +39,9 @@ public class CalendarUtils {
      * calendar system.
      * @see CalendarDate#isLeapYear
      */
-    public static final boolean isGregorianLeapYear(int gregorianYear) {
-        return (((gregorianYear % 4) == 0)
-                && (((gregorianYear % 100) != 0) || ((gregorianYear % 400) == 0)));
+    public static boolean isGregorianLeapYear(int gregorianYear) {
+        return (((gregorianYear % 4) == 0) && (((gregorianYear % 100) != 0)
+                || ((gregorianYear % 400) == 0)));
     }
 
     /**
@@ -51,7 +54,7 @@ public class CalendarUtils {
      * calendar system.
      * @see CalendarDate#isLeapYear
      */
-    public static final boolean isJulianLeapYear(int normalizedJulianYear) {
+    public static boolean isJulianLeapYear(int normalizedJulianYear) {
         return (normalizedJulianYear % 4) == 0;
     }
 
@@ -64,7 +67,7 @@ public class CalendarUtils {
      * @param d a divisor that must be greater than 0
      * @return the floor of the quotient
      */
-    public static final long floorDivide(long n, long d) {
+    public static long floorDivide(long n, long d) {
         return ((n >= 0) ?
                 (n / d) : (((n + 1L) / d) - 1L));
     }
@@ -78,7 +81,7 @@ public class CalendarUtils {
      * @param d a divisor that must be greater than 0
      * @return the floor of the quotient
      */
-    public static final int floorDivide(int n, int d) {
+    public static int floorDivide(int n, int d) {
         return ((n >= 0) ?
                 (n / d) : (((n + 1) / d) - 1));
     }
@@ -96,7 +99,7 @@ public class CalendarUtils {
      * <code>mod(n, d)</code> is returned.
      * @return the floor of the quotient.
      */
-    public static final int floorDivide(int n, int d, int[] r) {
+    public static int floorDivide(int n, int d, int[] r) {
         if (n >= 0) {
             r[0] = n % d;
             return n / d;
@@ -106,20 +109,20 @@ public class CalendarUtils {
         return q;
     }
 
-    public static final long mod(long x, long y) {
+    public static long mod(long x, long y) {
         return (x - y * floorDivide(x, y));
     }
 
-    public static final int mod(int x, int y) {
+    public static int mod(int x, int y) {
         return (x - y * floorDivide(x, y));
     }
 
-    public static final int amod(int x, int y) {
+    public static int amod(int x, int y) {
         int z = mod(x, y);
         return (z == 0) ? y : z;
     }
 
-    public static final long amod(long x, long y) {
+    public static long amod(long x, long y) {
         long z = mod(x, y);
         return (z == 0) ? y : z;
     }
@@ -127,7 +130,7 @@ public class CalendarUtils {
     /**
      * Mimics sprintf(buf, "%0*d", decaimal, width).
      */
-    public static final StringBuilder sprintf0d(StringBuilder sb, int value, int width) {
+    public static StringBuilder sprintf0d(StringBuilder sb, int value, int width) {
         long d = value;
         if (d < 0) {
             sb.append('-');
@@ -146,7 +149,7 @@ public class CalendarUtils {
         return sb;
     }
 
-    public static final StringBuffer sprintf0d(StringBuffer sb, int value, int width) {
+    public static StringBuffer sprintf0d(StringBuffer sb, int value, int width) {
         long d = value;
         if (d < 0) {
             sb.append('-');
diff --git a/src/java.base/share/classes/sun/util/calendar/Gregorian.java b/src/java.base/share/classes/sun/util/calendar/Gregorian.java
index d100687e4f5..c983814cecd 100644
--- a/src/java.base/share/classes/sun/util/calendar/Gregorian.java
+++ b/src/java.base/share/classes/sun/util/calendar/Gregorian.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2005, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -34,21 +34,23 @@ import java.util.TimeZone;
  * @since 1.5
  */
 
-public class Gregorian extends BaseCalendar {
+public final class Gregorian extends BaseCalendar {
 
-    static class Date extends BaseCalendar.Date {
-        protected Date() {
+    static final class Date extends BaseCalendar.Date {
+        Date() {
             super();
         }
 
-        protected Date(TimeZone zone) {
+        Date(TimeZone zone) {
             super(zone);
         }
 
+        @Override
         public int getNormalizedYear() {
             return getYear();
         }
 
+        @Override
         public void setNormalizedYear(int normalizedYear) {
             setYear(normalizedYear);
         }
@@ -57,30 +59,37 @@ public class Gregorian extends BaseCalendar {
     Gregorian() {
     }
 
+    @Override
     public String getName() {
         return "gregorian";
     }
 
+    @Override
     public Date getCalendarDate() {
         return getCalendarDate(System.currentTimeMillis(), newCalendarDate());
     }
 
+    @Override
     public Date getCalendarDate(long millis) {
         return getCalendarDate(millis, newCalendarDate());
     }
 
+    @Override
     public Date getCalendarDate(long millis, CalendarDate date) {
         return (Date) super.getCalendarDate(millis, date);
     }
 
+    @Override
     public Date getCalendarDate(long millis, TimeZone zone) {
         return getCalendarDate(millis, newCalendarDate(zone));
     }
 
+    @Override
     public Date newCalendarDate() {
         return new Date();
     }
 
+    @Override
     public Date newCalendarDate(TimeZone zone) {
         return new Date(zone);
     }
diff --git a/src/java.base/share/classes/sun/util/calendar/ImmutableGregorianDate.java b/src/java.base/share/classes/sun/util/calendar/ImmutableGregorianDate.java
index 3d9b2da548a..4836cab9886 100644
--- a/src/java.base/share/classes/sun/util/calendar/ImmutableGregorianDate.java
+++ b/src/java.base/share/classes/sun/util/calendar/ImmutableGregorianDate.java
@@ -25,192 +25,238 @@
 
 package sun.util.calendar;
 
+import java.util.Objects;
 import java.util.TimeZone;
 
-class ImmutableGregorianDate extends BaseCalendar.Date {
+/*
+ * This class is immutable, and thus any methods from the base classes
+ * that can modify the state are overridden to throw an exception.
+ */
+final class ImmutableGregorianDate extends BaseCalendar.Date {
     private final BaseCalendar.Date date;
 
     ImmutableGregorianDate(BaseCalendar.Date date) {
-        if (date == null) {
-            throw new NullPointerException();
-        }
-        this.date = date;
+        this.date = Objects.requireNonNull(date);
     }
 
+    @Override
     public Era getEra() {
         return date.getEra();
     }
 
+    @Override
     public CalendarDate setEra(Era era) {
         unsupported(); return this;
     }
 
+    @Override
     public int getYear() {
         return date.getYear();
     }
 
+    @Override
     public CalendarDate setYear(int year) {
         unsupported(); return this;
     }
 
+    @Override
     public CalendarDate addYear(int n) {
         unsupported(); return this;
     }
 
+    @Override
     public boolean isLeapYear() {
         return date.isLeapYear();
     }
 
+    @Override
     void setLeapYear(boolean leapYear) {
         unsupported();
     }
 
+    @Override
     public int getMonth() {
         return date.getMonth();
     }
 
+    @Override
     public CalendarDate setMonth(int month) {
         unsupported(); return this;
     }
 
+    @Override
     public CalendarDate addMonth(int n) {
         unsupported(); return this;
     }
 
+    @Override
     public int getDayOfMonth() {
         return date.getDayOfMonth();
     }
 
+    @Override
     public CalendarDate setDayOfMonth(int date) {
         unsupported(); return this;
     }
 
+    @Override
     public int getDayOfWeek() {
         return date.getDayOfWeek();
     }
 
+    @Override
     public int getHours() {
         return date.getHours();
     }
 
+    @Override
     public CalendarDate setHours(int hours) {
         unsupported(); return this;
     }
 
+    @Override
     public CalendarDate addHours(int n) {
         unsupported(); return this;
     }
 
+    @Override
     public int getMinutes() {
         return date.getMinutes();
     }
 
+    @Override
     public CalendarDate setMinutes(int minutes) {
         unsupported(); return this;
     }
 
+    @Override
     public int getSeconds() {
         return date.getSeconds();
     }
 
+    @Override
     public CalendarDate setSeconds(int seconds) {
         unsupported(); return this;
     }
 
+    @Override
     public int getMillis() {
         return date.getMillis();
     }
 
+    @Override
     public CalendarDate setMillis(int millis) {
         unsupported(); return this;
     }
 
+    @Override
     public long getTimeOfDay() {
         return date.getTimeOfDay();
     }
 
+    @Override
     public CalendarDate setDate(int year, int month, int dayOfMonth) {
         unsupported(); return this;
     }
 
+    @Override
     public CalendarDate setTimeOfDay(int hours, int minutes, int seconds, int millis) {
         unsupported(); return this;
     }
 
+    @Override
     protected void setTimeOfDay(long fraction) {
         unsupported();
     }
 
+    @Override
     public boolean isNormalized() {
         return date.isNormalized();
     }
 
+    @Override
     public boolean isDaylightTime() {
         return date.isDaylightTime();
     }
 
+    @Override
     public TimeZone getZone() {
         return date.getZone();
     }
 
+    @Override
     public CalendarDate setZone(TimeZone zoneinfo) {
         unsupported(); return this;
     }
 
+    @Override
     public boolean isSameDate(CalendarDate date) {
         return date.isSameDate(date);
     }
 
+    @Override
     public boolean equals(Object obj) {
         if (this == obj) {
             return true;
         }
-        if (!(obj instanceof ImmutableGregorianDate)) {
+        if (obj instanceof ImmutableGregorianDate igd) {
+            return date.equals(igd.date);
+        } else {
             return false;
         }
-        return date.equals(((ImmutableGregorianDate) obj).date);
     }
 
+    @Override
     public int hashCode() {
         return date.hashCode();
     }
 
+    @Override
     public Object clone() {
         return super.clone();
     }
 
+    @Override
     public String toString() {
         return date.toString();
     }
 
+    @Override
     protected void setDayOfWeek(int dayOfWeek) {
         unsupported();
     }
 
+    @Override
     protected void setNormalized(boolean normalized) {
         unsupported();
     }
 
+    @Override
     public int getZoneOffset() {
         return date.getZoneOffset();
     }
 
+    @Override
     protected void setZoneOffset(int offset) {
         unsupported();
     }
 
+    @Override
     public int getDaylightSaving() {
         return date.getDaylightSaving();
     }
 
+    @Override
     protected void setDaylightSaving(int daylightSaving) {
         unsupported();
     }
 
+    @Override
     public int getNormalizedYear() {
         return date.getNormalizedYear();
     }
 
+    @Override
     public void setNormalizedYear(int normalizedYear) {
         unsupported();
     }
diff --git a/src/java.base/share/classes/sun/util/calendar/JulianCalendar.java b/src/java.base/share/classes/sun/util/calendar/JulianCalendar.java
index 8129090d295..49bdaa60cd9 100644
--- a/src/java.base/share/classes/sun/util/calendar/JulianCalendar.java
+++ b/src/java.base/share/classes/sun/util/calendar/JulianCalendar.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003, 2005, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -33,7 +33,7 @@ import java.util.TimeZone;
  * @author Masayoshi Okutsu
  * @since 1.5
  */
-public class JulianCalendar extends BaseCalendar {
+public final class JulianCalendar extends BaseCalendar {
 
     private static final int BCE = 0;
     private static final int CE = 1;
@@ -44,17 +44,18 @@ public class JulianCalendar extends BaseCalendar {
     };
     private static final int JULIAN_EPOCH = -1;
 
-    private static class Date extends BaseCalendar.Date {
-        protected Date() {
+    static final class Date extends BaseCalendar.Date {
+        Date() {
             super();
             setCache(1, -1L, 365); // January 1, 1 CE (Julian)
         }
 
-        protected Date(TimeZone zone) {
+        Date(TimeZone zone) {
             super(zone);
             setCache(1, -1L, 365); // January 1, 1 CE (Julian)
         }
 
+        @Override
         public Date setEra(Era era) {
             if (era == null) {
                 throw new NullPointerException();
@@ -66,10 +67,11 @@ public class JulianCalendar extends BaseCalendar {
             return this;
         }
 
-        protected void setKnownEra(Era era) {
+        void setKnownEra(Era era) {
             super.setEra(era);
         }
 
+        @Override
         public int getNormalizedYear() {
             if (getEra() == eras[BCE]) {
                 return 1 - getYear();
@@ -81,6 +83,7 @@ public class JulianCalendar extends BaseCalendar {
         // normalized years. This differs from "Calendrical
         // Calculations" in which the numbering is ..., -2, -1, 1, 2,
         // ...
+        @Override
         public void setNormalizedYear(int year) {
             if (year <= 0) {
                 setYear(1 - year);
@@ -91,6 +94,7 @@ public class JulianCalendar extends BaseCalendar {
             }
         }
 
+        @Override
         public String toString() {
             String time = super.toString();
             time = time.substring(time.indexOf('T'));
@@ -114,30 +118,37 @@ public class JulianCalendar extends BaseCalendar {
         setEras(eras);
     }
 
+    @Override
     public String getName() {
         return "julian";
     }
 
+    @Override
     public Date getCalendarDate() {
         return getCalendarDate(System.currentTimeMillis(), newCalendarDate());
     }
 
+    @Override
     public Date getCalendarDate(long millis) {
         return getCalendarDate(millis, newCalendarDate());
     }
 
+    @Override
     public Date getCalendarDate(long millis, CalendarDate date) {
         return (Date) super.getCalendarDate(millis, date);
     }
 
+    @Override
     public Date getCalendarDate(long millis, TimeZone zone) {
         return getCalendarDate(millis, newCalendarDate(zone));
     }
 
+    @Override
     public Date newCalendarDate() {
         return new Date();
     }
 
+    @Override
     public Date newCalendarDate(TimeZone zone) {
         return new Date(zone);
     }
@@ -145,6 +156,7 @@ public class JulianCalendar extends BaseCalendar {
     /**
      * @param jyear normalized Julian year
      */
+    @Override
     public long getFixedDate(int jyear, int month, int dayOfMonth, BaseCalendar.Date cache) {
         boolean isJan1 = month == JANUARY && dayOfMonth == 1;
 
@@ -182,6 +194,7 @@ public class JulianCalendar extends BaseCalendar {
         return days;
     }
 
+    @Override
     public void getCalendarDateFromFixedDate(CalendarDate date, long fixedDate) {
         Date jdate = (Date) date;
         long fd = 4 * (fixedDate - JULIAN_EPOCH) + 1464;
@@ -216,18 +229,18 @@ public class JulianCalendar extends BaseCalendar {
     /**
      * Returns the normalized Julian year number of the given fixed date.
      */
+    @Override
     public int getYearFromFixedDate(long fixedDate) {
-        int year = (int) CalendarUtils.floorDivide(4 * (fixedDate - JULIAN_EPOCH) + 1464, 1461);
-        return year;
+        return (int) CalendarUtils.floorDivide(4 * (fixedDate - JULIAN_EPOCH) + 1464, 1461);
     }
 
+    @Override
     public int getDayOfWeek(CalendarDate date) {
-        // TODO: should replace this with a faster calculation, such
-        // as cache table lookup
-        long fixedDate = getFixedDate(date);
-        return getDayOfWeekFromFixedDate(fixedDate);
+        // TODO: should replace with faster calculation, e.g. cache table lookup
+        return getDayOfWeekFromFixedDate(getFixedDate(date));
     }
 
+    @Override
     boolean isLeapYear(int jyear) {
         return CalendarUtils.isJulianLeapYear(jyear);
     }
diff --git a/src/java.base/share/classes/sun/util/calendar/LocalGregorianCalendar.java b/src/java.base/share/classes/sun/util/calendar/LocalGregorianCalendar.java
index 283adca6b59..cb567e8c052 100644
--- a/src/java.base/share/classes/sun/util/calendar/LocalGregorianCalendar.java
+++ b/src/java.base/share/classes/sun/util/calendar/LocalGregorianCalendar.java
@@ -36,7 +36,7 @@ import sun.security.action.GetPropertyAction;
  * @since 1.6
  */
 
-public class LocalGregorianCalendar extends BaseCalendar {
+public final class LocalGregorianCalendar extends BaseCalendar {
     private static final Era[] JAPANESE_ERAS = {
         new Era("Meiji",  "M", -3218832000000L, true),
         new Era("Taisho", "T", -1812153600000L, true),
@@ -63,13 +63,14 @@ public class LocalGregorianCalendar extends BaseCalendar {
     private String name;
     private Era[] eras;
 
-    public static class Date extends BaseCalendar.Date {
+    // Used within java.time and java.util
+    public static final class Date extends BaseCalendar.Date {
 
-        protected Date() {
+        Date() {
             super();
         }
 
-        protected Date(TimeZone zone) {
+        Date(TimeZone zone) {
             super(zone);
         }