使用FutureTask和Callable创建可获取返回值的多线程

import java.util.concurrent.Callable;import java.util.concurrent.FutureTask;public class CallableThread {public static void main(String[] args){FutureTask<Integer> task=new FutureTask<Integer>((Callable<Integer>)()->{int i=0;for(;i<100;i++){System.out.println(Thread.currentThread().getName()+"  i "+i);}return i;});for(int i=0;i<100;i++){System.out.println(Thread.currentThread().getName()+"   "+i);if(i==20){new Thread(task).start();}} try {System.out.println("return value of task "+task.get());} catch (Exception e) {e.printStackTrace();}}}