5066247: Refine the spec of equals() and hashCode() for j.text.Format classes

Reviewed-by: naoto, darcy

src/java.base/share/classes/java/text/DecimalFormatSymbols.java

@@ -737,7 +737,17 @@ public class DecimalFormatSymbols implements Cloneable, Serializable {
     }
 
     /**
-     * Override equals.
+     * Compares the specified object with this {@code DecimalFormatSymbols} for equality.
+     * Returns true if the object is also a {@code DecimalFormatSymbols} and the two
+     * {@code DecimalFormatSymbols} objects represent the same set of symbols.
+     *
+     * @implSpec This method performs an equality check with a notion of class
+     * identity based on {@code getClass()}, rather than {@code instanceof}.
+     * Therefore, in the equals methods in subclasses, no instance of this class
+     * should compare as equal to an instance of a subclass.
+     * @param  obj object to be compared for equality
+     * @return {@code true} if the specified object is equal to this {@code DecimalFormatSymbols}
+     * @see Object#equals(Object)
      */
     @Override
     public boolean equals(Object obj) {
@@ -767,7 +777,11 @@ public class DecimalFormatSymbols implements Cloneable, Serializable {
     }
 
     /**
-     * Override hashCode.
+     * {@return the hash code for this {@code DecimalFormatSymbols}}
+     *
+     * @implSpec Non-transient instance fields of this class are used to calculate
+     * a hash code value which adheres to the contract defined in {@link Objects#hashCode}.
+     * @see Object#hashCode()
      */
     @Override
     public int hashCode() {