OpenJDK Proposes Sequenced Collections for Java’s Future
The Java programming language could soon see a significant update to its collections framework with the introduction of sequenced collections, sequenced sets, and sequenced maps. This enhancement would address long-standing concerns about Java’s ability to represent collections with a defined encounter order. The proposal suggests adding new interfaces that establish encounter order as a first-class concept, making collections more intuitive and feature-rich for developers.
Currently under consideration in the OpenJDK community, this proposal aims to define interfaces for sequenced collections and retrofit them into Java’s existing type hierarchy. Java developers have often pointed out that although classes like List and Deque maintain a defined order, the overarching Collection interface does not provide such guarantees. As a result, developers lack a unified way to work with ordered collections, which can lead to inconsistencies and limited flexibility when manipulating data structures.
The proposal identifies two major gaps in Java’s current collections framework: the absence of a generic collection type that consistently represents a sequence with a defined order and the lack of uniform operations applicable across all such collections. These issues have been a source of frustration, and the new interfaces aim to streamline operations on ordered collections. This would bring more cohesion to Java’s design, making it easier for developers to work with collections that maintain a predictable element order.
All new methods introduced in these sequenced collection interfaces would come with default implementations, ensuring backward compatibility and smooth integration into the existing framework. If approved, the sequenced collections feature would be added to the standard edition of Java, with JDK 20 as the earliest potential release. With JDK 19 having just been released, this proposal underscores Java’s commitment to evolving and refining its features as part of the language’s regular six-month release cycle.