4993841: (str) java.lang.Character should have a toString(int) method

Reviewed-by: martin, rriggs, sherman, smarks

src/java.base/share/classes/java/lang/Character.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2002, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2002, 2018, 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
@@ -7568,6 +7568,11 @@ class Character implements java.io.Serializable, Comparable<Character> {
      * specified {@code char}.  The result is a string of length
      * 1 consisting solely of the specified {@code char}.
      *
+     * @apiNote This method cannot handle <a
+     * href="#supplementary"> supplementary characters</a>. To support
+     * all Unicode characters, including supplementary characters, use
+     * the {@link #toString(int)} method.
+     *
      * @param c the {@code char} to be converted
      * @return the string representation of the specified {@code char}
      * @since 1.4
@@ -7576,6 +7581,22 @@ class Character implements java.io.Serializable, Comparable<Character> {
         return String.valueOf(c);
     }
 
+    /**
+     * Returns a {@code String} object representing the
+     * specified character (Unicode code point).  The result is a string of
+     * length 1 or 2, consisting solely of the specified {@code codePoint}.
+     *
+     * @param codePoint the {@code codePoint} to be converted
+     * @return the string representation of the specified {@code codePoint}
+     * @exception IllegalArgumentException if the specified
+     *      {@code codePoint} is not a {@linkplain #isValidCodePoint
+     *      valid Unicode code point}.
+     * @since 11
+     */
+    public static String toString(int codePoint) {
+        return String.valueOfCodePoint(codePoint);
+    }
+
     /**
      * Determines whether the specified code point is a valid
      * <a href="http://www.unicode.org/glossary/#code_point">

src/java.base/share/classes/java/lang/String.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1994, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1994, 2018, 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
@@ -3157,4 +3157,27 @@ public final class String
                 "begin " + begin + ", end " + end + ", length " + length);
         }
     }
+
+    /**
+     * Returns the string representation of the {@code codePoint}
+     * argument.
+     *
+     * @param   codePoint a {@code codePoint}.
+     * @return  a string of length {@code 1} or {@code 2} containing
+     *          as its single character the argument {@code codePoint}.
+     * @throws IllegalArgumentException if the specified
+     *          {@code codePoint} is not a {@linkplain Character#isValidCodePoint
+     *          valid Unicode code point}.
+     */
+    static String valueOfCodePoint(int codePoint) {
+        if (COMPACT_STRINGS && StringLatin1.canEncode(codePoint)) {
+            return new String(StringLatin1.toBytes((char)codePoint), LATIN1);
+        } else if (Character.isBmpCodePoint(codePoint)) {
+            return new String(StringUTF16.toBytes((char)codePoint), UTF16);
+        } else if (Character.isSupplementaryCodePoint(codePoint)) {
+            return new String(StringUTF16.toBytesSupplementary(codePoint), UTF16);
+        }
+
+        throw new IllegalArgumentException("Not a valid Unicode code point");
+    }
 }

src/java.base/share/classes/java/lang/StringUTF16.java

@@ -235,6 +235,13 @@ final class StringUTF16 {
         return result;
     }
 
+    static byte[] toBytesSupplementary(int cp) {
+        byte[] result = new byte[4];
+        putChar(result, 0, Character.highSurrogate(cp));
+        putChar(result, 1, Character.lowSurrogate(cp));
+        return result;
+    }
+
     @HotSpotIntrinsicCandidate
     public static void getChars(byte[] value, int srcBegin, int srcEnd, char dst[], int dstBegin) {
         // We need a range check here because 'getChar' has no checks