Doctypes - short for 'document type' - help browsers to understand the version of HTML the document is written in for better interpretability. Doctype declarations are not HTML tags and belong at the very top of a document. This topic explains the structure and declaration of various doctypes in HTML.
Java Atomic Types are simple mutable types that provide basic operations that are thread-safe and atomic without resorting to locking. They are intended for use in cases where locking would be a concurrency bottleneck, or where there is risk of deadlock or livelock.