142 Java Functional Programming

This is a comprehensive refactoring assistant that applies modern Java functional programming patterns to your codebase. It covers the essentials like immutable Records, Streams, and Optional, plus newer features like pattern matching, sealed classes, and Stream Gatherers from Java 21. What makes it solid is the safety-first approach: it won't touch your code unless the project compiles first, and it verifies everything afterward with a full Maven build. The reference material includes good and bad examples for each pattern, so you get concrete guidance on moving side effects to boundaries and keeping your core logic pure. If you're modernizing a Java codebase or just tired of null checks and mutable state, this walks you through the transformation methodically.

skills.sh installs: 135
GitHub stars: 393
last updated: Jun 3, 2026

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Install

$ npx -y skills add jabrena/cursor-rules-java --skill 142-java-functional-programming --agent claude-code

Installs into .claude/skills of the current project.

Files

Java Functional Programming rules

Identify and apply functional programming principles in Java to improve immutability, expressiveness, and maintainability.

What is covered in this Skill?

Immutable objects and Records (JEP 395)
Pure functions free of side effects
Functional interfaces: Function, Predicate, Consumer, Supplier, custom @FunctionalInterface
Lambda expressions and method references
Stream API: filter/map/reduce pipelines, parallel streams, toUnmodifiable* collectors
Optional idiomatic usage: map/flatMap/filter/orElse* over isPresent()+get()
Function composition: andThen/compose
Higher-order functions: memoization, currying, partial application
Pattern Matching for instanceof and switch (Java 21)
Sealed classes and interfaces (Java 17) for exhaustive domain hierarchies
Switch Expressions (Java 14), Stream Gatherers (JEP 461)
Effect-boundary separation: side effects at edges, pure core logic
Immutable collections: List.of(), Collectors.toUnmodifiableList()