• Java Collections Framework (JCF) Overview: Since Java's inception, the JCF has been a consistent backbone. It has seen improvements like generics and concurrency but remains largely the same. Collections are essential in Java apps, and learning to use JCF interfaces and classes is a must for Java developers.
• Series Overview: This series dives into Java collections. Starting with general concepts and the collections interface (this article), each primary collection data structure (Lists, Sets, and Queues) will get a dedicated article. By the end, readers will understand the fundamentals and advanced topics of each.
• History of JCF: In Java's early days, no common collection framework existed. Java lagged behind C++ in creating one. Popular collection frameworks before JDK 2 were JGL and Collections Package. Joshua Bloch designed much of the JCF using JGL. JDK 2 introduced a basic collections framework, and JDK 5 added generics and concurrency.
• Concept of a Collection: In Java, a collection represents a group of objects. It has vague definitions regarding element grouping, accessibility, and duplicates. Collections must support adding, removing, and iterating over elements, and provide queries and conversions to arrays. With JDK 8, they must also convert to a stream.
• Collection Interface: The Collection interface in Java captures collection responsibilities. It is parameterized with a generic type E. Methods include size, isEmpty, contains, iterator, toArray, add, remove, etc. Each method has specific behaviors and uses.
• Implicit Rules: While some collection rules are checked at compile-time, others are extra-linguistic. All collection implementations should have a no-args constructor and a conversion constructor. Unsupported destructive methods should throw an UnsupportedOperationException. Synchronization is determined by each implementation.
• Collection Hierarchy: The JCF's power comes from various interfaces, abstract classes, and concrete implementations. Three prominent types are List (ordered collection), Set (no duplicates), and Queue (for processing with specific ordering). Each has its constraints and features, and will be covered in future articles.
• Recommended Resources: If interested in learning more about Java Collections, check out a collection of tutorials and articles on DZone.