Groovy & Gradle: JVM Automation and Build Engineering · 课时

使用 Groovy 实现函数式模式

应用闭包和集合方法，在 Groovy 代码中实现函数式编程模式。

第 3 / 4 课11 个步骤

使用 Groovy 实现函数式模式 是 CoddyKit 上的免费 Groovy & Gradle: JVM Automation and Build Engineering 课时。这是第 3 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 Groovy & Gradle: JVM Automation and Build Engineering 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Groovy & Gradle: JVM Automation and Build Engineering 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Functional Groovy: An Introduction

Welcome to Functional Patterns with Groovy! In this lesson, we'll explore how to write more expressive and maintainable code using a functional style.

Functional programming is a paradigm that treats computation as the evaluation of mathematical functions and avoids changing state and mutable data. Groovy's closures and enhanced collection methods make it a fantastic language for adopting these patterns.

Why Functional Programming?

Adopting a functional style offers several benefits:

Cleaner Code: Often more concise and readable.
Easier Testing: Functions without 'side effects' are predictable.
Reduced Bugs: Less mutable state means fewer unexpected changes.
Concurrency: Easier to parallelize operations.

We'll focus on patterns that transform data without altering the original collections.

Iteration vs. Transformation

Before diving into functional transformations, let's look at a common imperative way to process a list using each. While useful for side effects (like printing), it doesn't create new, transformed collections.

Functional patterns, on the other hand, focus on producing new collections from existing ones, leaving the originals untouched.

class Main {
  static void main(String[] args) {
    List numbers = [1, 2, 3]
    print("Original: ")
    numbers.each { num ->
      print("$num ")
    }
    println("\nThis doesn't create a new list.")
  }
}

`collect`: Mapping Data

The collect method is Groovy's equivalent of the map operation. It takes a closure and applies it to each element in a collection, returning a new list with the transformed elements.

This is a core functional pattern for data transformation.

class Main {
  static void main(String[] args) {
    List numbers = [1, 2, 3, 4]
    List doubledNumbers = numbers.collect { it * 2 }
    println("Original: $numbers")
    println("Doubled: $doubledNumbers")
  }
}

`findAll`: Filtering Data

The findAll method (similar to filter) selects elements from a collection that satisfy a given condition. The closure you provide should return true or false for each element.

It also returns a new list containing only the elements that passed the filter.

class Main {
  static void main(String[] args) {
    List numbers = [1, 2, 3, 4, 5, 6]
    List evenNumbers = numbers.findAll { it % 2 == 0 }
    println("Original: $numbers")
    println("Evens: $evenNumbers")
  }
}

`inject`: Reducing Collections

The inject method (also known as reduce or fold) is used to combine all elements in a collection into a single result. You provide an initial value and a closure that takes two arguments: the accumulator and the current element.

It's powerful for summing, concatenating, or performing complex aggregations.

class Main {
  static void main(String[] args) {
    List numbers = [1, 2, 3, 4]
    // Calculate sum starting with 0
    def sum = numbers.inject(0) { total, num -> total + num }
    println("Numbers: $numbers")
    println("Sum: $sum")
  }
}

Chaining Functional Calls

One of the great advantages of functional patterns is the ability to chain operations. Since methods like collect and findAll return new collections, you can call another collection method directly on the result.

This creates readable data processing pipelines.

class Main {
  static void main(String[] args) {
    List products = [
      [name: "Laptop", price: 1200, stock: 5],
      [name: "Mouse", price: 25, stock: 20],
      [name: "Keyboard", price: 75, stock: 0]
    ]
    
    def expensiveAvailableProductNames = products
      .findAll { it.stock > 0 && it.price > 50 }
      .collect { it.name.toUpperCase() }
          
    println("Products: $products")
    println("Expensive Available: $expensiveAvailableProductNames")
  }
}

Custom Sorting with `sort`

Groovy's sort method is very flexible. When given a closure, it uses that closure to determine the sorting order. The closure should take two arguments (a and b) and return a negative, zero, or positive integer if a is less than, equal to, or greater than b, respectively.

class Main {
  static void main(String[] args) {
    List words = ["apple", "banana", "cat", "dog"]
    // Sort by length, then alphabetically if lengths are equal
    List sortedWords = words.sort { a, b ->
      def lengthComparison = a.length() <=> b.length()
      return lengthComparison != 0 ? lengthComparison : a <=> b
    }
    println("Original: $words")
    println("Sorted: $sortedWords")
  }
}

`groupBy`: Categorizing Data

The groupBy method is excellent for organizing data into categories. It takes a closure that determines the key for each element. The result is a Map where keys are the values returned by the closure, and values are lists of elements belonging to that category.

class Main {
  static void main(String[] args) {
    List people = [
      [name: "Alice", age: 30, city: "NY"],
      [name: "Bob", age: 25, city: "LA"],
      [name: "Charlie", age: 30, city: "NY"],
      [name: "David", age: 35, city: "LA"]
    ]
    
    def peopleByCity = people.groupBy { it.city }
    println("People: $people")
    println("Grouped by City: $peopleByCity")
  }
}

Functional Flow Challenge

Test your understanding of chaining functional operations!

在交互式课程中回答

Recap: Functional Groovy

Great job! You've explored how to apply functional programming patterns in Groovy:

collect: Transforms elements into a new list.
findAll: Filters elements based on a condition.
inject: Reduces a collection to a single value.
sort: Customizes sorting with closures.
groupBy: Categorizes elements into a map.

By chaining these methods, you can build powerful, readable, and maintainable data processing pipelines. Keep practicing to master this elegant style!

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应用闭包和集合方法，在 Groovy 代码中实现函数式编程模式。你通过在浏览器中直接运行的动手代码来练习 Groovy & Gradle: JVM Automation and Build Engineering，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

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