Java 9 introduced several important enhancements that improved modularity, maintainability, developer productivity, and application performance. The most significant addition was the Java Platform Module System (JPMS), which allows applications to be organized into well-defined modules with explicit dependencies.
Key Points: • The Module System (Project Jigsaw) enables better dependency management, stronger encapsulation, and modular application design. • JShell was introduced as an interactive REPL tool, allowing developers to test Java code snippets without creating full programs. • Stream API, Optional, Collection APIs, and Process APIs were enhanced, making code more expressive and easier to maintain.
Major Java 9 Features:
1. Module System (JPMS) • Introduced module-info.java. • Allows applications to be split into independent modules. • Improves maintainability, security, and scalability.
2. JShell • Interactive command-line tool for executing Java statements. • Useful for learning, experimentation, and quick testing.
3. Stream API Enhancements • Added takeWhile(), dropWhile(), and iterate() improvements. • Simplifies data processing operations.
4. Optional API Improvements • Added ifPresentOrElse(), stream(), and or() methods. • Improves null handling and code readability.
5. Factory Methods for Collections • Added List.of(), Set.of(), and Map.of(). • Simplifies immutable collection creation.
6. Process API Enhancements • Improved support for process management and monitoring. • Allows access to process information and child processes.
7. Private Methods in Interfaces • Interfaces can now contain private helper methods. • Reduces code duplication among default methods.
Example: In a large banking application, Java 9 modules allow separate modules such as customer, account, payment, and reporting to expose only necessary APIs while hiding internal implementation details, resulting in a cleaner and more secure architecture.
Code Example:
module com.bank.payment {
requires com.bank.account;
exports com.bank.payment.service;
}Interview Tip: A concise interview answer is: Java 9 introduced the Module System, JShell, Stream API enhancements, Collection factory methods, Optional improvements, and better process management. The Module System had the biggest impact because it enabled modular application development, stronger encapsulation, easier dependency management, and improved maintainability for large-scale applications.