SONARJAVA-5589 modify S1643: add performance benchmark table

rules/S1643/java/rule.adoc

@@ -26,6 +26,50 @@ StringBuilder bld = new StringBuilder();
 ----
 
 
+[options="header"]
+|===
+| Method| size| Runtime| Average time| Error margin
+| plus| 100| Temurin 21| 4.19 us/op| ±0.34 us/op
+| plus| 1000| Temurin 21| 377.08 us/op| ±17.36 us/op
+| plus| 10000| Temurin 21| 40221.49 us/op| ±1342.76 us/op
+| plus| 100000| Temurin 21| 5286.84 ms/op| ±185.79 ms/op
+| stringBuilder| 100| Temurin 21| 0.97 us/op| ±0.03 us/op
+| stringBuilder| 1000| Temurin 21| 10.25 us/op| ±1.64 us/op
+| stringBuilder| 10000| Temurin 21| 93.27 us/op| ±16.05 us/op
+| stringBuilder| 100000| Temurin 21| 1.01 ms/op| ±0.06 ms/op
+|===
+
+
+*Benchmarking code*
+
+The results were generated by running the following snippet with https://github.com/openjdk/jmh[JMH].
+
+[source,java]
+----
+@Param({"100", "1000", "10000", "100000"})
+int size;
+private String word = "append";
+
+@Benchmark
+public String plus() {
+  String str = "";
+  for (int i = 0; i < size; i++) {
+    str = str + word;
+  }
+  return str;
+}
+
+@Benchmark
+public String stringBuilder() {
+  StringBuilder builder = new StringBuilder();
+  for (int i = 0; i < size; i++) {
+    builder.append(word);
+  }
+  return builder.toString();
+}
+----
+
+
 ifdef::env-github,rspecator-view[]
 
 '''