Hi Ganesh,
Responses to your fine questions.
> Will The Java Performance Companion book be useful for 2+ year experienced Java developer?
It might ;-)
If you have interest in wanting to know more details of the G1 garbage collector, how it works, how to tune it, then yes it should be useful.
If you have interest in either wanting to learn about some of the internal parts of the HotSpot JVM, or have interest in how to triage a situation that resulted in an unexpected JVM failure, then the content on the HotSpot Serviceability Agent would be useful.
If there are other areas of Java performance that may be of interest, than a look at the table of content of the Java Performance might be of some interest.
> Does this book provide examples to show, how to write code to improve the performance of an application?
No it does not provide examples on how to write code to improve the performance of an application. It focuses more on either tuning G1 GC, through some examples, or how to use the Serviceability Agent, again through examples.
As for how to write code to improve performance of an application ... you may have seen in one of the other threads here there is a suggestion to write code in its most natural form along with a couple suggestions to think about? I suppose I could add to that and say that choosing / using the most appropriate data structures and algorithms fit into that "writing code in its natural form" description.
> Does this book provide diagrammtic representation where necessary to understand the concepts like GC mechanism?
Yes there are diagrams in both the GC content and Serviceability Agent content.