pkg19performance

Performance

5 files in study order.

1. 01StringConcatBenchmarkpkg19performance/jmh-demo/src/main/java/pkg19performance/jmh/StringConcatBenchmark.java
2. 02GcAllocationDemopkg19performance/performance1GcAllocationDemo.java
3. 03JvmFlagsGuidepkg19performance/performance2JvmFlagsGuide.java
4. 04JfrConceptspkg19performance/performance3JfrConcepts.java
5. 05GraalVmNativeImagepkg19performance/performance4GraalVmNativeImage.java