When building complex applications, you need to manipulate collections of objects in different ways. Initially, the core Java library was limited to only three options: Array, Vector, and Hashtable. All of them are powerful in their own way, but with time, it became clear that wasn't enough. People started building their own frameworks to deal with more complex use cases such as grouping, sorting, and comparing.
The Java Collections Framework was added to Java Standard Edition to reduce programming effort and improve the performance and interoperability of Java applications by providing data structures and algorithms that are efficient and easy to use. This set of interfaces and implementing classes were designed to provide an easy way for Java developers to build APIs that could be shared and reused.