(Update 05-19-2020) There are a lot of online code playground or white boarding tools for code testing on the spot.
(Original ) Hibernate map one to many (Vlad Mihalcea)
A collection of the posts I saw recently.
Introduction to Java threads
Java Callable Future Example
Vaadin chat example
It needs multi session (thread) support when we need to use tabs to chat back and forth. The app description is here.
The annotation to support this: @VaadinSessionScope
Java interview questions
Placeholder: I still need to clean up the list below (to incorporate my recent interview experience).
code review (what to look)
static vs. final
tree set vs hash set
tree map vs linked hash map
.equals() vs ==