8371732: [redo] Change java.time month/day field types to 'byte'

Reviewed-by: darcy, alanb

Author: Roger Riggs

src/java.base/share/classes/java/time/LocalDate.java

@@ -79,6 +79,8 @@
 import java.io.IOException;
 import java.io.InvalidObjectException;
 import java.io.ObjectInputStream;
+import java.io.ObjectStreamField;
+import java.io.Serial;
 import java.io.Serializable;
 import java.time.chrono.ChronoLocalDate;
 import java.time.chrono.IsoEra;
@@ -142,6 +144,22 @@
 public final class LocalDate
         implements Temporal, TemporalAdjuster, ChronoLocalDate, Serializable {
 
+    /**
+     * For backward compatibility of the serialized {@code LocalDate.class} object,
+     * explicitly declare the types of the serialized fields as defined in Java SE 8.
+     * Instances of {@code LocalDate} are serialized using the dedicated
+     * serialized form by {@code writeReplace}.
+     * @serialField year int The year.
+     * @serialField month short The month-of-year.
+     * @serialField day short The day-of-month.
+     */
+    @Serial
+    private static final ObjectStreamField[] serialPersistentFields = {
+            new ObjectStreamField("year", int.class),
+            new ObjectStreamField("month", short.class),
+            new ObjectStreamField("day", short.class)
+    };
+
     /**
      * The minimum supported {@code LocalDate}, '-999999999-01-01'.
      * This could be used by an application as a "far past" date.
@@ -178,15 +196,15 @@ public final class LocalDate
     /**
      * @serial The year.
      */
-    private final int year;
+    private final transient int year;
     /**
      * @serial The month-of-year.
      */
-    private final short month;
+    private final transient byte month;
     /**
      * @serial The day-of-month.
      */
-    private final short day;
+    private final transient byte day;
 
     //-----------------------------------------------------------------------
     /**
@@ -490,8 +508,8 @@ private static LocalDate resolvePreviousValid(int year, int month, int day) {
      */
     private LocalDate(int year, int month, int dayOfMonth) {
         this.year = year;
-        this.month = (short) month;
-        this.day = (short) dayOfMonth;
+        this.month = (byte) month;
+        this.day = (byte) dayOfMonth;
     }
 
     //-----------------------------------------------------------------------

src/java.base/share/classes/java/time/MonthDay.java

@@ -69,6 +69,8 @@
 import java.io.IOException;
 import java.io.InvalidObjectException;
 import java.io.ObjectInputStream;
+import java.io.ObjectStreamField;
+import java.io.Serial;
 import java.io.Serializable;
 import java.time.chrono.Chronology;
 import java.time.chrono.IsoChronology;
@@ -133,6 +135,20 @@ public final class MonthDay
      */
     @java.io.Serial
     private static final long serialVersionUID = -939150713474957432L;
+
+    /**
+     * For backward compatibility of the serialized {@code MonthDay.class} object,
+     * explicitly declare the types of the serialized fields as defined in Java SE 8.
+     * Instances of {@code MonthDay} are serialized using the dedicated
+     * serialized form by {@code writeReplace}.
+     * @serialField month int The month-of-year.
+     * @serialField day int The day-of-month.
+     */
+    @Serial
+    private static final ObjectStreamField[] serialPersistentFields = {
+            new ObjectStreamField("month", int.class),
+            new ObjectStreamField("day", int.class)
+    };
     /**
      * Parser.
      */
@@ -144,13 +160,13 @@ public final class MonthDay
         .toFormatter();
 
     /**
-     * @serial The month-of-year, not null.
+     * @serial The month-of-year.
      */
-    private final int month;
+    private final transient byte month;
     /**
      * @serial The day-of-month.
      */
-    private final int day;
+    private final transient byte day;
 
     //-----------------------------------------------------------------------
     /**
@@ -319,8 +335,8 @@ public static MonthDay parse(CharSequence text, DateTimeFormatter formatter) {
      * @param dayOfMonth  the day-of-month to represent, validated from 1 to 29-31
      */
     private MonthDay(int month, int dayOfMonth) {
-        this.month = month;
-        this.day = dayOfMonth;
+        this.month = (byte) month;
+        this.day = (byte) dayOfMonth;
     }
 
     //-----------------------------------------------------------------------

src/java.base/share/classes/java/time/YearMonth.java

@@ -78,6 +78,8 @@
 import java.io.IOException;
 import java.io.InvalidObjectException;
 import java.io.ObjectInputStream;
+import java.io.ObjectStreamField;
+import java.io.Serial;
 import java.io.Serializable;
 import java.time.chrono.Chronology;
 import java.time.chrono.IsoChronology;
@@ -137,6 +139,20 @@ public final class YearMonth
      */
     @java.io.Serial
     private static final long serialVersionUID = 4183400860270640070L;
+
+    /**
+     * For backward compatibility of the serialized {@code YearMonth.class} object,
+     * explicitly declare the types of the serialized fields as defined in Java SE 8.
+     * Instances of {@code YearMonth} are serialized using the dedicated
+     * serialized form by {@code writeReplace}.
+     * @serialField year int The year.
+     * @serialField month int The month-of-year.
+     */
+    @java.io.Serial
+    private static final ObjectStreamField[] serialPersistentFields = {
+            new ObjectStreamField("year", int.class),
+            new ObjectStreamField("month", int.class),
+    };
     /**
      * Parser.
      */
@@ -149,11 +165,11 @@ public final class YearMonth
     /**
      * @serial The year.
      */
-    private final int year;
+    private final transient int year;
     /**
-     * @serial The month-of-year, not null.
+     * @serial The month-of-year..
      */
-    private final int month;
+    private final transient byte month;
 
     //-----------------------------------------------------------------------
     /**
@@ -306,7 +322,7 @@ public static YearMonth parse(CharSequence text, DateTimeFormatter formatter) {
      */
     private YearMonth(int year, int month) {
         this.year = year;
-        this.month = month;
+        this.month = (byte) month;
     }
 
     /**

src/java.base/share/classes/java/time/chrono/HijrahDate.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2025, 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
@@ -137,11 +137,11 @@ public final class HijrahDate
     /**
      * The month-of-year.
      */
-    private final transient int monthOfYear;
+    private final transient byte monthOfYear;
     /**
      * The day-of-month.
      */
-    private final transient int dayOfMonth;
+    private final transient byte dayOfMonth;
 
     //-------------------------------------------------------------------------
     /**
@@ -273,8 +273,8 @@ private HijrahDate(HijrahChronology chrono, int prolepticYear, int monthOfYear,
 
         this.chrono = chrono;
         this.prolepticYear = prolepticYear;
-        this.monthOfYear = monthOfYear;
-        this.dayOfMonth = dayOfMonth;
+        this.monthOfYear = (byte) monthOfYear;
+        this.dayOfMonth = (byte) dayOfMonth;
     }
 
     /**
@@ -287,8 +287,8 @@ private HijrahDate(HijrahChronology chrono, long epochDay) {
 
         this.chrono = chrono;
         this.prolepticYear = dateInfo[0];
-        this.monthOfYear = dateInfo[1];
-        this.dayOfMonth = dateInfo[2];
+        this.monthOfYear = (byte) dateInfo[1];
+        this.dayOfMonth = (byte) dateInfo[2];
     }
 
     //-----------------------------------------------------------------------

test/jdk/java/time/test/java/time/TestLocalDate.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2025, 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
@@ -65,6 +65,8 @@
 import static org.testng.Assert.assertTrue;
 import static org.testng.Assert.fail;
 
+import java.io.ObjectStreamClass;
+import java.io.ObjectStreamField;
 import java.time.DateTimeException;
 import java.time.LocalDate;
 import java.time.Month;
@@ -515,4 +517,18 @@ public void test_minus_QuarterYears(long quarterYears) {
                 .minus(quarterYears, ChronoUnit.MONTHS);
         assertEquals(t0, t1);
     }
+
+    // Verify serialized fields types are backward compatible
+    @Test
+    public void verifySerialFields() {
+        var osc = ObjectStreamClass.lookup(LocalDate.class);
+        for (ObjectStreamField f : osc.getFields()) {
+            switch (f.getName()) {
+                case "year" -> assertEquals(f.getType(), int.class, f.getName());
+                case "month",
+                     "day" -> assertEquals(f.getType(), short.class);
+                default -> fail("unknown field in LocalDate: " + f.getName());
+            }
+        }
+    }
 }

test/jdk/java/time/test/java/time/TestMonthDay.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2025, 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
@@ -62,7 +62,10 @@
 import static org.testng.Assert.assertEquals;
 import static org.testng.Assert.assertSame;
 import static org.testng.Assert.assertTrue;
+import static org.testng.Assert.fail;
 
+import java.io.ObjectStreamClass;
+import java.io.ObjectStreamField;
 import java.time.LocalDate;
 import java.time.Month;
 import java.time.MonthDay;
@@ -144,4 +147,17 @@ void doTest_comparisons_MonthDay(MonthDay... localDates) {
         }
     }
 
+
+    // Verify serialized fields types are backward compatible
+    @Test
+    public void verifySerialFields() {
+        var osc = ObjectStreamClass.lookup(MonthDay.class);
+        for (ObjectStreamField f : osc.getFields()) {
+            switch (f.getName()) {
+                case "month",
+                     "day" -> assertEquals(f.getType(), int.class, f.getName());
+                default -> fail("unknown field in MonthDay: " + f.getName());
+            }
+        }
+    }
 }

test/jdk/java/time/test/java/time/TestYearMonth.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2025, 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
@@ -59,10 +59,16 @@
  */
 package test.java.time;
 
+import java.io.ObjectStreamClass;
+import java.io.ObjectStreamField;
+import java.time.LocalDate;
 import java.time.YearMonth;
 
 import org.testng.annotations.Test;
 
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.fail;
+
 /**
  * Test YearMonth.
  */
@@ -75,4 +81,16 @@ public void test_immutable() {
         assertImmutable(YearMonth.class);
     }
 
+    // Verify serialized fields types are backward compatible
+    @Test
+    public void verifySerialFields() {
+        var osc = ObjectStreamClass.lookup(YearMonth.class);
+        for (ObjectStreamField f : osc.getFields()) {
+            switch (f.getName()) {
+                case "year" -> assertEquals(f.getType(), int.class, f.getName());
+                case "month" -> assertEquals(f.getType(), int.class, f.getName());
+                default -> fail("unknown field in YearMonth: " + f.getName());
+            }
+        }
+    }
 }