Functional Programming Best Practices in Java
| Practice | Description |
|---|---|
| Prefer immutability | Avoid changing object state; use final variables and immutable data structures. |
| Use pure functions | Functions should not have side effects (e.g., modifying global state or I/O). |
| Avoid shared mutable state | Ensures thread-safety and better modularity in concurrent environments. |
| Use functional interfaces effectively | Leverage built-in ones (Function, Predicate, etc.) and create custom ones. |
| Favor declarative over imperative | Describe what to do using Streams, not how (avoid loops and manual logic). |
| Chain operations with Streams | Use operations like map(), filter(), and collect() fluently. |
| Minimize side effects in lambdas | Avoid modifying external variables in lambda expressions. |
| Use method references | Improve readability where lambdas just call existing methods. |
| Use Optional to handle nulls | Avoid null checks by wrapping results in Optional. |
| Avoid stateful operations in streams | Ensure stream operations don’t depend on mutable or external state. |
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Common Functional Coding Patterns in Java
| Pattern | Description | Example Usage |
|---|---|---|
| Map | Transform elements from one type to another. | list.stream().map(String::length) |
| Filter | Select elements based on a condition. | list.stream().filter(s -> s.length() > 3) |
| Reduce | Combine elements to a single value. | stream.reduce(0, Integer::sum) |
| Compose functions | Use andThen() / compose() to chain functions. |
f1.andThen(f2) |
| Lazy evaluation | Streams evaluate elements only when needed (terminal ops like collect). |
Avoid unnecessary computation |
| Currying | Transform a function that takes multiple arguments into a chain of functions. | Simulated with lambdas (manually nested) |
| Memoization | Cache expensive computations (not built-in; implement manually if needed). | Useful for performance in recursive tasks |
| Predicate chaining | Combine conditions with and(), or(), negate(). |
p1.and(p2).negate() |
| Optional chaining | Use map(), flatMap(), orElse() on Optional for safe value handling. |
Optional.of(value).map(...).orElse(...) |
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Functional programming in Java encourages writing clean, modular, testable, and thread-safe code. By adhering to best practices like using pure functions, avoiding shared state, and leveraging powerful coding patterns like map, filter, and reduce, developers can unlock a more expressive and efficient coding style — blending the strengths of both OOP and FP paradigms in modern Java development.