Why IntelliJ IDEA 2025.3’s New Islands Theme and AI Features Matter for Java Developers

Core Feature Highlights

01 Islands New Theme

IntelliJ IDEA 2025.3 switches the default theme to Islands, offering a softer look with higher contrast and clear workspace separation. The theme improves focus and readability compared to the previous Dark theme.

The new theme’s design aims to help developers stay focused and code comfortably.

Screenshot comparisons illustrate the Islands Dark appearance versus the classic Dark theme.

02 Support for Spring Boot 4 and Java 25

The update adds native support for Spring Boot 4 and JDK 25, enabling developers to start projects with the latest stack. Notable enhancements include:

API version control using the @GetMapping annotation’s version field.

Improved Java 25 support, the upcoming LTS release scheduled for September 2025.

Compatibility with newer tools such as JUnit 6 and Gradle 9.

Reference link to JetBrains blog for Java 25 LTS details.

03 Full‑Line Code Completion

After updating to 2025.3, a prompt appears to download a code‑completion patch. Enabling “full line code completion” allows developers to trigger suggestions with . or .., view context actions, and preview changes.

Press . to see code and suffix completions.

Press .. to filter results to actions only.

Select an action to view detailed context and preview the resulting code.

04 Integration of Claude Code AI Plugin

The official Claude Code plugin can be installed from the marketplace. If the Claude Code tool is already installed via NPM, it can be used directly within IDEA. The author recommends generating code in a terminal with Claude Code and reviewing/optimizing it in IDEA.

Images show the plugin installation and usage UI.

Conclusion

After more than ten years with IDEA, the author finds the 2025.3 release impressive: the Islands theme improves visual comfort, Spring Boot 4 and Java 25 support enables early adoption of new technologies, and full‑line code completion narrows the gap between traditional IDEs and AI‑first editors.

While AI capabilities still lag behind dedicated AI editors, IDEA remains a robust, enterprise‑grade IDE for refactoring, debugging, and performance analysis.