多线程ForkJoinPool

 import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;
import java.util.concurrent.TimeUnit;

public class ForkJoin {
 private List<String> list = new ArrayList<String>();
 private int groupNum =5; //分成5个小任务,分别获取list中的值
 
 public void init() {
  for(int i=0;i<20;i++) {
   list.add("a" + i);
  }
 }
 
 public static void main(String[] args) {
  
  System.out.println("*");
  ForkJoinPool pool = new ForkJoinPool();
  ForkJoin a = new ForkJoin();
  a.init();
  int size = a.list.size();
  Task task = a.new Task(0, size);
  
  System.out.println("**");
  pool.submit(task);
  System.out.println("***");
  try {
   pool.awaitTermination(2, TimeUnit.SECONDS);
  } catch (InterruptedException e) {
   e.printStackTrace();
  }
  //阻塞当前线程直到 pool 中所有的任务都执行结束
  // 关闭线程池
  System.out.println("****");
  pool.shutdown();
  
 }

 class Task extends RecursiveAction{
  private static final int MIN_SIZE = 8;
  private int start;
  private int end;
  
  public Task(int start, int end) {
   this.start = start;
   this.end = end;
  }

  protected void compute() {
   boolean canCompute = end-start<=MIN_SIZE?true:false;
   if(canCompute) {
    System.out.println("...");
    for(int i=start;i<=end;i++) {
     print(i);
    }
   }else {
    System.out.println("---");
    int pos = start;
    int step = (end - start)/groupNum;
    for(int i=0;i<groupNum;i++) {
     int last = pos + step;
     if(last> end) {
      last = end;
     }
     System.out.println("pos=" + pos + ", end=" + last);
     Task t = new Task(pos, last);
     pos += step + 1;
     t.fork();
    }
    
   }
  }
  
  void print(int i) {
   System.out.println(Thread.currentThread().getName() + "    " +list.get(i));
  }
 }
}