8272687: Replace StringBuffer with StringBuilder in RuleBasedCollator

Reviewed-by: lancea, naoto, bchristi, bpb

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

@@ -243,7 +243,7 @@ short getMaxTerOrder() {
      */
     //shemran/Note: this is used for secondary order value reverse, no
     //              need to consider supplementary pair.
-    static void reverse (StringBuffer result, int from, int to)
+    static void reverse (StringBuilder result, int from, int to)
     {
         int i = from;
         char swap;

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2022, 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
@@ -605,9 +605,9 @@ public synchronized CollationKey getCollationKey(String source)
             return null;
 
         if (primResult == null) {
-            primResult = new StringBuffer();
-            secResult = new StringBuffer();
-            terResult = new StringBuffer();
+            primResult = new StringBuilder();
+            secResult = new StringBuilder();
+            terResult = new StringBuilder();
         } else {
             primResult.setLength(0);
             secResult.setLength(0);
@@ -681,8 +681,8 @@ public synchronized CollationKey getCollationKey(String source)
         }
         primResult.append((char)0);
         secResult.append((char)0);
-        secResult.append(terResult.toString());
-        primResult.append(secResult.toString());
+        secResult.append(terResult);
+        primResult.append(secResult);
 
         if (getStrength() == IDENTICAL) {
             primResult.append((char)0);
@@ -762,9 +762,9 @@ RBCollationTables getTables() {
 
     // Internal objects that are cached across calls so that they don't have to
     // be created/destroyed on every call to compare() and getCollationKey()
-    private StringBuffer primResult = null;
-    private StringBuffer secResult = null;
-    private StringBuffer terResult = null;
+    private StringBuilder primResult = null;
+    private StringBuilder secResult = null;
+    private StringBuilder terResult = null;
     private CollationElementIterator sourceCursor = null;
     private CollationElementIterator targetCursor = null;
 }