--- /dev/null	2015-07-25 15:02:20.097409468 -0700
+++ new/test/java/lang/String/CompactString/Concat.java	2015-10-30 14:04:09.683236348 -0700
@@ -0,0 +1,132 @@
+/*
+ * Copyright (c) 2015, 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.
+ */
+
+import org.testng.annotations.DataProvider;
+import org.testng.annotations.Test;
+
+import static org.testng.Assert.assertEquals;
+
+/*
+ * @test
+ * @bug 8077559
+ * @summary Tests Compact String. This one is for String.concat.
+ * @run testng/othervm -XX:+CompactStrings Concat
+ * @run testng/othervm -XX:-CompactStrings Concat
+ */
+
+public class Concat extends CompactString {
+
+    @DataProvider
+    public Object[][] provider() {
+        return new Object[][] {
+                new Object[] { STRING_EMPTY, "ABC", "ABC" },
+                new Object[] { STRING_EMPTY,
+                        "ABC".concat("\uFF21\uFF22\uFF23").concat("DEF"),
+                        "ABC\uFF21\uFF22\uFF23DEF" },
+                new Object[] {
+                        STRING_EMPTY,
+                        "\uFF21\uFF22\uFF23".concat("ABC").concat(
+                                "\uFF24\uFF25\uFF26"),
+                        "\uFF21\uFF22\uFF23ABC\uFF24\uFF25\uFF26" },
+                new Object[] { STRING_L1,
+                        "ABC".concat("\uFF21\uFF22\uFF23").concat("DEF"),
+                        "AABC\uFF21\uFF22\uFF23DEF" },
+                new Object[] {
+                        STRING_L1,
+                        "\uFF21\uFF22\uFF23".concat("ABC").concat(
+                                "\uFF24\uFF25\uFF26"),
+                        "A\uFF21\uFF22\uFF23ABC\uFF24\uFF25\uFF26" },
+                new Object[] { STRING_L2,
+                        "ABC".concat("\uFF21\uFF22\uFF23").concat("DEF"),
+                        "ABABC\uFF21\uFF22\uFF23DEF" },
+                new Object[] {
+                        STRING_L2,
+                        "\uFF21\uFF22\uFF23".concat("ABC").concat(
+                                "\uFF24\uFF25\uFF26"),
+                        "AB\uFF21\uFF22\uFF23ABC\uFF24\uFF25\uFF26" },
+                new Object[] { STRING_L4,
+                        "ABC".concat("\uFF21\uFF22\uFF23").concat("DEF"),
+                        "ABCDABC\uFF21\uFF22\uFF23DEF" },
+                new Object[] {
+                        STRING_L4,
+                        "\uFF21\uFF22\uFF23".concat("ABC").concat(
+                                "\uFF24\uFF25\uFF26"),
+                        "ABCD\uFF21\uFF22\uFF23ABC\uFF24\uFF25\uFF26" },
+                new Object[] { STRING_LLONG,
+                        "ABC".concat("\uFF21\uFF22\uFF23").concat("DEF"),
+                        "ABCDEFGHABC\uFF21\uFF22\uFF23DEF" },
+                new Object[] {
+                        STRING_LLONG,
+                        "\uFF21\uFF22\uFF23".concat("ABC").concat(
+                                "\uFF24\uFF25\uFF26"),
+                        "ABCDEFGH\uFF21\uFF22\uFF23ABC\uFF24\uFF25\uFF26" },
+                new Object[] { STRING_U1,
+                        "ABC".concat("\uFF21\uFF22\uFF23").concat("DEF"),
+                        "\uFF21ABC\uFF21\uFF22\uFF23DEF" },
+                new Object[] {
+                        STRING_U1,
+                        "\uFF21\uFF22\uFF23".concat("ABC").concat(
+                                "\uFF24\uFF25\uFF26"),
+                        "\uFF21\uFF21\uFF22\uFF23ABC\uFF24\uFF25\uFF26" },
+                new Object[] { STRING_U2,
+                        "ABC".concat("\uFF21\uFF22\uFF23").concat("DEF"),
+                        "\uFF21\uFF22ABC\uFF21\uFF22\uFF23DEF" },
+                new Object[] {
+                        STRING_U2,
+                        "\uFF21\uFF22\uFF23".concat("ABC").concat(
+                                "\uFF24\uFF25\uFF26"),
+                        "\uFF21\uFF22\uFF21\uFF22\uFF23ABC\uFF24\uFF25\uFF26" },
+                new Object[] { STRING_M12,
+                        "ABC".concat("\uFF21\uFF22\uFF23").concat("DEF"),
+                        "\uFF21AABC\uFF21\uFF22\uFF23DEF" },
+                new Object[] {
+                        STRING_M12,
+                        "\uFF21\uFF22\uFF23".concat("ABC").concat(
+                                "\uFF24\uFF25\uFF26"),
+                        "\uFF21A\uFF21\uFF22\uFF23ABC\uFF24\uFF25\uFF26" },
+                new Object[] { STRING_M11,
+                        "ABC".concat("\uFF21\uFF22\uFF23").concat("DEF"),
+                        "A\uFF21ABC\uFF21\uFF22\uFF23DEF" },
+                new Object[] {
+                        STRING_M11,
+                        "\uFF21\uFF22\uFF23".concat("ABC").concat(
+                                "\uFF24\uFF25\uFF26"),
+                        "A\uFF21\uFF21\uFF22\uFF23ABC\uFF24\uFF25\uFF26" }, };
+    }
+
+    @Test(dataProvider = "provider")
+    public void testConcat(String str, String anotherString, String expected) {
+        map.get(str)
+                .forEach(
+                        (source, data) -> {
+                            assertEquals(
+                                    data.concat(anotherString),
+                                    expected,
+                                    String.format(
+                                            "testing String(%s).concat(%s), source : %s, ",
+                                            escapeNonASCIIs(data),
+                                            escapeNonASCIIs(anotherString),
+                                            source));
+                        });
+    }
+}