142-java-functional-programming

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Chinese

Java Functional Programming rules

Java 函数式编程规则

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()

Scope: The reference is organized by examples (good/bad code patterns) for each core area. Apply recommendations based on applicable examples.

识别并在Java中应用函数式编程原则，以提升不可变性、表达性和可维护性。

本Skill涵盖哪些内容？

不可变对象与Records（JEP 395）
无副作用的纯函数

函数式接口：

Function

、

Predicate

、

Consumer

、

Supplier

、自定义

@FunctionalInterface

Lambda表达式与方法引用
Stream API：filter/map/reduce管道、并行流、
```
toUnmodifiable*
```
收集器

Optional

的惯用用法：优先使用

map

flatMap

filter

orElse*

而非

isPresent()

get()

函数组合：
```
andThen
```
/
```
compose
```
高阶函数：记忆化、柯里化、部分应用
```
instanceof
```
和switch的模式匹配（Java 21）
密封类与接口（Java 17）：用于穷尽式领域层级
Switch表达式（Java 14）、Stream Gatherers（JEP 461）
副作用边界分离：副作用仅在边缘处理，核心逻辑保持纯函数

不可变集合：

List.of()

、

Collectors.toUnmodifiableList()

范围：参考文档按每个核心领域的示例（好/坏代码模式）组织。请根据适用的示例应用建议。

Constraints

约束条件

Before applying any functional programming changes, ensure the project compiles. If compilation fails, stop immediately — do not proceed until the project compiles successfully. Verify that maven-compiler-plugin source/target supports the Java features being used.

MANDATORY: Run
```
./mvnw compile
```
or
```
mvn compile
```
before applying any changes
SAFETY: If compilation fails, stop immediately — do not proceed until the project compiles successfully
VERIFY: Verify maven-compiler-plugin source/target supports the Java features being used
VERIFY: Run
```
./mvnw clean verify
```
or
```
mvn clean verify
```
after applying improvements
BEFORE APPLYING: Read the reference for detailed good/bad examples, constraints, and safeguards for each functional programming pattern

在应用任何函数式编程变更之前，确保项目能够编译。如果编译失败，请立即停止——在项目成功编译前不要继续。验证maven-compiler-plugin的source/target是否支持所使用的Java特性。

强制要求：在应用任何变更前运行
```
./mvnw compile
```
或
```
mvn compile
```
安全提示：如果编译失败，请立即停止——在项目成功编译前不要继续
验证：确认maven-compiler-plugin的source/target支持所使用的Java特性
验证：在应用改进后运行
```
./mvnw clean verify
```
或
```
mvn clean verify
```
应用前：阅读参考文档，了解每个函数式编程模式的详细好/坏示例、约束条件和防护措施

When to use this skill

何时使用本Skill

Improve the code with Functional Programming
Apply Functional Programming
Refactor the code with Functional Programming

使用函数式编程改进代码
应用函数式编程
使用函数式编程重构代码

Reference

参考资料

For detailed guidance, examples, and constraints, see references/142-java-functional-programming.md.

如需详细指导、示例和约束条件，请查看references/142-java-functional-programming.md。