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

Reviewed-by: naoto, darcy

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

@@ -698,7 +698,11 @@ public abstract class NumberFormat extends Format  {
     }
 
     /**
-     * Overrides hashCode.
+     * {@return the hash code for this {@code NumberFormat}}
+     *
+     * @implSpec This method calculates the hash code value using the values returned by
+     * {@link #getMaximumIntegerDigits()} and {@link #getMaximumFractionDigits()}.
+     * @see Object#hashCode()
      */
     @Override
     public int hashCode() {
@@ -707,7 +711,17 @@ public abstract class NumberFormat extends Format  {
     }
 
     /**
-     * Overrides equals.
+     * Compares the specified object with this {@code NumberFormat} for equality.
+     * Returns true if the object is also a {@code NumberFormat} and the
+     * two formats would format any value the same.
+     *
+     * @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 NumberFormat}
+     * @see Object#equals(Object)
      */
     @Override
     public boolean equals(Object obj) {