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

@@ -281,14 +281,24 @@
      * @exception        ArithmeticException if rounding is needed with rounding
      *                   mode being set to RoundingMode.UNNECESSARY
      * @see java.text.Format#format
      */
     public final String format(double number) {
+        // Use fast-path for double result if that works
+        String result = fastFormat(number);
+        if (result != null) return result;
+
         return format(number, new StringBuffer(),
                       DontCareFieldPosition.INSTANCE).toString();
     }
 
+    /*
+     * fastFormat() is supposed to be implemented in concrete subclasses only.
+     * Default implem always returns null.
+     */
+    String fastFormat(double number) { return null; }
+
    /**
      * Specialization of format.
      * @exception        ArithmeticException if rounding is needed with rounding
      *                   mode being set to RoundingMode.UNNECESSARY
      * @see java.text.Format#format