Add a new test with String.join()

Author: Arthur Aukhatov

README.md

@@ -22,6 +22,9 @@ StringBenchmark.stringConcat                            50  avgt   10   76.619 
 StringBenchmark.stringFormat                            10  avgt   10  673.458 ± 26.151  ns/op
 StringBenchmark.stringFormat                            20  avgt   10  711.718 ± 50.907  ns/op
 StringBenchmark.stringFormat                            50  avgt   10  733.963 ± 29.483  ns/op
+StringBenchmark.stringJoin                              10  avgt   10   92.567 ±  1.582  ns/op
+StringBenchmark.stringJoin                              20  avgt   10  121.745 ±  5.397  ns/op
+StringBenchmark.stringJoin                              50  avgt   10  182.598 ±  1.253  ns/op
 ```
 
 ### Conclusion

src/main/java/art/aukhatov/string/StringBenchmark.java

@@ -58,6 +58,13 @@ public String stringBuilder(Dictionary dictionary, Blackhole bh) {
         return message;
     }
 
+    @Benchmark
+    public String stringJoin(Dictionary dictionary, Blackhole bh) {
+        String message = String.join("Hello", dictionary.word, dictionary.word);
+        bh.consume(message);
+        return message;
+    }
+
     @State(Scope.Thread)
     public static class Dictionary {