Java 函数式编程 - 并行执行

并行执行是函数式编程的一个关键概念，它通过把大任务分解成更小的独立任务来完成，然后以并行方式完成这些小任务，最后将结果合并在一起得到完整的结果。随着多核处理器的出现，此技术有助于更快地执行代码。Java 有基于线程的编程支持以实现并行处理，但它比较难学，而且不借助错误很难实现。从 Java 8 起，流有 parallel 方法，集合有 parallelStream() 方法，可并行完成任务。请看以下示例

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class FunctionTester {
   public static void main(String[] args) {

      Integer[] intArray = {1, 2, 3, 4, 5, 6, 7, 8 };
      List<Integer> listOfIntegers = new ArrayList<>(Arrays.asList(intArray));

      System.out.println("List using Serial Stream:");
      listOfIntegers
         .stream()
         .forEach(e -> System.out.print(e + " "));
      System.out.println("");

      System.out.println("List using Parallel Stream:");
      listOfIntegers
         .parallelStream()
         .forEach(e -> System.out.print(e + " "));
      System.out.println("");

      System.out.println("List using Another Parallel Stream:");
      listOfIntegers
         .stream()
         .parallel()
         .forEach(e -> System.out.print(e + " "));
      System.out.println("");

      System.out.println("List using Parallel Stream but Ordered:");
      listOfIntegers
         .parallelStream()
         .forEachOrdered(e -> System.out.print(e + " "));
         System.out.println(""); 
   } 
}

输出

List using Serial Stream:
1 2 3 4 5 6 7 8 
List using Parallel Stream:
6 5 8 7 3 4 2 1 
List using Another Parallel Stream:
6 2 1 7 4 3 8 5 
List using Parallel Stream but Ordered:
1 2 3 4 5 6 7 8