8148937: (str) Adapt StringJoiner for Compact Strings

Reviewed-by: redestad, chegar

src/java.base/share/classes/java/util/StringJoiner.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, 2021, 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
@@ -148,12 +148,6 @@ public final class StringJoiner {
         return this;
     }
 
-    private static int getChars(String s, char[] chars, int start) {
-        int len = s.length();
-        s.getChars(0, len, chars, start);
-        return len;
-    }
-
     /**
      * Returns the current value, consisting of the {@code prefix}, the values
      * added so far separated by the {@code delimiter}, and the {@code suffix},
@@ -170,22 +164,21 @@ public final class StringJoiner {
         }
         final int size = this.size;
         final int addLen = prefix.length() + suffix.length();
-        if (addLen == 0) {
+        if (size == 0) {
-            compactElts();
+            if (addLen == 0) {
-            return size == 0 ? "" : elts[0];
+                return "";
+            }
+            return prefix + suffix;
         }
         final String delimiter = this.delimiter;
-        final char[] chars = new char[len + addLen];
+        StringBuilder sb = new StringBuilder(len + addLen).append(prefix);
-        int k = getChars(prefix, chars, 0);
         if (size > 0) {
-            k += getChars(elts[0], chars, k);
+            sb.append(elts[0]);
             for (int i = 1; i < size; i++) {
-                k += getChars(delimiter, chars, k);
+                sb.append(delimiter).append(elts[i]);
-                k += getChars(elts[i], chars, k);
             }
         }
-        k += getChars(suffix, chars, k);
+        return sb.append(suffix).toString();
-        return new String(chars);
     }
 
     /**
@@ -249,15 +242,14 @@ public final class StringJoiner {
 
     private void compactElts() {
         if (size > 1) {
-            final char[] chars = new char[len];
+            StringBuilder sb = new StringBuilder(len).append(elts[0]);
-            int i = 1, k = getChars(elts[0], chars, 0);
+            int i = 1;
             do {
-                k += getChars(delimiter, chars, k);
+                sb.append(delimiter).append(elts[i]);
-                k += getChars(elts[i], chars, k);
                 elts[i] = null;
             } while (++i < size);
             size = 1;
-            elts[0] = new String(chars);
+            elts[0] = sb.toString();
         }
     }
 

test/micro/org/openjdk/bench/java/util/StringJoinerBenchmark.java

@@ -0,0 +1,111 @@
+/*
+ * Copyright (c) 2018, 2021, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package org.openjdk.bench.java.util;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+
+import java.util.StringJoiner;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Trivial benchmark for String joining with {@link java.util.StringJoiner}.
+ */
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@Fork(jvmArgsAppend = {"-Xms2g", "-Xmx2g"})
+public class StringJoinerBenchmark {
+
+    @Benchmark
+    public String stringJoiner(Data data) {
+        String[] stringArray = data.stringArray;
+        return Joiner.joinWithStringJoiner(stringArray);
+    }
+
+    @State(Scope.Thread)
+    public static class Data {
+
+        @Param({"latin", "cyrillic"})
+        private String mode;
+
+        @Param({"8", "32"})
+        private int length;
+
+        @Param({"5", "10"})
+        private int count;
+
+        private String[] stringArray;
+
+        @Setup
+        public void setup() {
+            stringArray = new String[count];
+
+            for (int i = 0; i < count; i++) {
+                String alphabet = getAlphabet(i, mode);
+                stringArray[i] = randomString(alphabet, length);
+            }
+        }
+
+        private String randomString(String alphabet, int length) {
+            var tl = ThreadLocalRandom.current();
+            StringBuilder sb = new StringBuilder();
+            for (int i = 0; i < length; i++) {
+                sb.append(alphabet.charAt(tl.nextInt(alphabet.length())));
+            }
+            return sb.toString();
+        }
+
+        private static String getAlphabet(int index, String mode) {
+            var latin = "abcdefghijklmnopqrstuvwxyz"; //English
+            StringBuilder sb = new StringBuilder();
+            latin.codePoints().forEach(cp -> sb.append(cp - 'a' + '\u0430'));
+            var cyrillic = sb.toString(); // Russian (partial, matching length of latin alphabet)
+
+            String alphabet;
+            switch (mode) {
+                case "latin" -> alphabet = latin;
+                case "cyrillic" -> alphabet = cyrillic;
+                default -> throw new RuntimeException("Illegal mode " + mode);
+            }
+            return alphabet;
+        }
+    }
+}
+
+class Joiner {
+    public static String joinWithStringJoiner(String[] stringArray) {
+        StringJoiner joiner = new StringJoiner(",", "[", "]");
+        for (String str : stringArray) {
+            joiner.add(str);
+        }
+        return joiner.toString();
+    }
+}