In this article "Improvements in Java Collection API" we will learn about the origin of classes in different versions of jdk. Also, If any new class or interface introduced, what was the purpose of introducing that? What was the weakness of previous version of it? Why the new class/interface introduced? What all new features introduced in Collection classes/interfaces? and so on. We are going to discuss about these kinds of questions in this article accordingly. In fact, we will learn about Enhancement of java collection classes step by step & also version by version simultaneously. Primarily, we will focus on Java collection features in JDK 1.0, 1.2, 1.4, 1.5, 1.6 and 1.8, 9 10, 11, 21 respectively. Improvements in Java Collection