Java 9, released in September 2017, introduced several significant features to enhance the Java programming language. One of the most notable additions is the Java Platform Module System, which allows developers to modularize their applications, improving maintainability and scalability. This modularity helps in managing dependencies more effectively. Another key feature of Java 9 is the JShell, a Read-Eval-Print Loop (REPL) tool that enables developers to test code snippets interactively. Additionally, Java 9 includes improvements to the Stream API, making it easier to work with collections of data. These enhancements aim to streamline development and improve performance.