SONARJAVA-5587 S4635 Add benchmark for Java

rules/S4635/java/rule.adoc

@@ -32,4 +32,57 @@ str.substring(beginIndex).indexOf(char1); // Noncompliant; a new String is going
 str.indexOf(char1, beginIndex) - beginIndex; // index for char1 not found is (-1-beginIndex)
 ----
 
+== Resources
+
+=== Benchmarks
+
+[options="header"]
+|===
+| Method| stringSize| Runtime| Average time| Error margin
+| indexOfOnly| 10| Temurin 21| 1.55 ns/op| ±0.12 ns/op
+| indexOfOnly| 100| Temurin 21| 1.78 ns/op| ±0.05 ns/op
+| indexOfOnly| 1000| Temurin 21| 1.82 ns/op| ±0.18 ns/op
+| indexOfOnly| 10000| Temurin 21| 1.77 ns/op| ±0.08 ns/op
+| substringThenIndexOf| 10| Temurin 21| 4.85 ns/op| ±0.41 ns/op
+| substringThenIndexOf| 100| Temurin 21| 6.22 ns/op| ±0.40 ns/op
+| substringThenIndexOf| 1000| Temurin 21| 14.22 ns/op| ±1.66 ns/op
+| substringThenIndexOf| 10000| Temurin 21| 275.00 ns/op| ±20.49 ns/op
+|===
+
+*Benchmarking code*
+
+The results were generated by running the following snippet with https://github.com/openjdk/jmh[JMH].
+
+[source,java]
+----
+@BenchmarkMode({Mode.AverageTime})
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Benchmark)
+public class S4635 {
+  @Param({"10", "100", "1000", "10000"})
+  int stringSize;
+
+  String input;
+
+  @Setup
+  public void setup() {
+    StringBuilder builder = new StringBuilder();
+    for (int i = 0; i < stringSize; i++) {
+      builder.append('a');
+    }
+    input = builder.toString();
+  }
+
+  @Benchmark
+  public int substringThenIndexOf() {
+    return stringSize / 2 + input.substring(stringSize / 2).indexOf('a');
+  }
+
+  @Benchmark
+  public int indexOfOnly() {
+    return input.indexOf('a', stringSize / 2);
+  }
+}
+----
+
 include::../rspecator.adoc[]