Summary

Make the cached hash code in java.text.DecimalFormatSymbols not serializable by adding transient keyword to its field declaration.

Problem

Since JDK15, java.text.DecimalFormatSymbols started caching the hash code which is lazily initialized at the first hashCode() invocation. As the field is declared as non-transient, the value is serialized and reused when it is read in readObject(). Although it won't cause any issue if serialize/deserialize is being done in JDK15 as the value calculation is fixed, the code should not rely on that implementation detail, as hash codes are not required to remain consistent beyond JVM invocations.

Solution

Add transient keyword to the cached hash code field so that it won't be serialized. The field will always be zero-reset on each object construction so that the value is calculated on its first invocation of hashCode() method.

Specification

Change the cached hash code field declaration as follows:

-- a/src/java.base/share/classes/java/text/DecimalFormatSymbols.java
+++ b/src/java.base/share/classes/java/text/DecimalFormatSymbols.java
@@ -760,7 +760,6 @@
     /**
      * Override hashCode.
      */
-    private volatile int hashCode;
     @Override
     public int hashCode() {
         if (hashCode == 0) {
@@ -1148,6 +1147,11 @@
     private transient Currency currency;
     private transient volatile boolean currencyInitialized;

+    /**
+     * Cached hash code.
+     */
+    private transient volatile int hashCode;
+
     // Proclaim JDK 1.1 FCS compatibility
     @java.io.Serial
     static final long serialVersionUID = 5772796243397350300L;