8318761: MessageFormat pattern support for CompactNumberFormat, ListFormat, and DateTimeFormatter

Reviewed-by: naoto, rriggs

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

@@ -482,6 +482,31 @@ public abstract class DateFormat extends Format {
      */
     public static final int DEFAULT = MEDIUM;
 
+    /**
+     * A DateFormat style.
+     * {@code Style} is an enum which corresponds to the DateFormat style
+     * constants. Use {@code getValue()} to retrieve the associated int style
+     * value.
+     */
+    enum Style {
+
+        FULL(DateFormat.FULL),
+        LONG(DateFormat.LONG),
+        MEDIUM(DateFormat.MEDIUM),
+        SHORT(DateFormat.SHORT),
+        DEFAULT(DateFormat.MEDIUM);
+
+        private final int value;
+
+        Style(int value){
+            this.value = value;
+        }
+
+        int getValue() {
+            return value;
+        }
+    }
+
     /**
      * Gets the time formatter with the default formatting style
      * for the default {@link java.util.Locale.Category#FORMAT FORMAT} locale.

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1996, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1996, 2024, 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
@@ -677,6 +677,33 @@ public abstract class NumberFormat extends Format  {
         return getInstance(locale, formatStyle, COMPACTSTYLE);
     }
 
+    /**
+     * This method compares the passed NumberFormat to a number of pre-defined
+     * style NumberFormat instances, (created with the passed locale). Returns a
+     * matching FormatStyle string if found, otherwise null.
+     * This method is used by MessageFormat to provide string pattens for NumberFormat
+     * Subformats. Any future pre-defined NumberFormat styles should be added to this method.
+     */
+    static String matchToStyle(NumberFormat fmt, Locale locale) {
+        if (fmt.equals(NumberFormat.getInstance(locale))) {
+            return "";
+        } else if (fmt.equals(NumberFormat.getCurrencyInstance(locale))) {
+            return "currency";
+        } else if (fmt.equals(NumberFormat.getPercentInstance(locale))) {
+            return "percent";
+        } else if (fmt.equals(NumberFormat.getIntegerInstance(locale))) {
+            return "integer";
+        } else if (fmt.equals(NumberFormat.getCompactNumberInstance(locale,
+                NumberFormat.Style.SHORT))) {
+            return "compact_short";
+        } else if (fmt.equals(NumberFormat.getCompactNumberInstance(locale,
+                NumberFormat.Style.LONG))) {
+            return "compact_long";
+        } else {
+            return null;
+        }
+    }
+
     /**
      * Returns an array of all locales for which the
      * {@code get*Instance} methods of this class can return