验证Future.get阻塞性，阻塞的是什么

package com.fengjr.p2passet.riskcontrol.web.loan;

import com.fengjr.p2passet.service.auto.thread.pool.ProcessRejectedExecutionHandler;
import com.fengjr.p2passet.service.auto.thread.pool.ThreadPool;
import com.google.common.collect.Lists;
import lombok.Data;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class Test {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService service = new ThreadPoolExecutor(5,10,5,TimeUnit.SECONDS,new LinkedBlockingQueue<Runnable>(20),Executors.defaultThreadFactory(),
                new ProcessRejectedExecutionHandler());
        List<Future<?>> futures = new ArrayList<Future<?>>(100);
        @Data
        class Temp {
            int iT;
        }

        List<Temp> list = new ArrayList(20);
        for (int i=0; i<20; i++) {
            Temp temp = new Temp();
            temp.setIT(i);

            list.add(temp);
        }
        for(int i=0;i<20;i++){
            final Temp temp = list.get(i);
            Future<?> future = service.submit( new Callable<String>() {
                @Override
                public String call() throws Exception {
                    String threadName = Thread.currentThread().getName();
                    System. out.println("线程任务" + temp.getIT() + ",线程"+threadName+"在进行计算");
                    if(temp.getIT() == 2){
                        System. out.println("提交的线程任务"+temp.getIT()+",线程"+threadName+"现在休眠");
                        Thread.sleep(5000);
                        System. out.println("提交的线程任务" + temp.getIT()+",线程"+threadName+",醒来！！！！");
                    }
                    //Thread.sleep(3000);
                    return "线程任务" + temp.getIT()+",线程名称"+threadName;
                }
            });
            futures.add(future);
        }
        //System. out.println("主线程---------------------" + Thread.currentThread ().getName() + "在执行任务" );
        for(Future<?> item:futures){
            try {
                System. out.println("线程运行结果---------------" + item.get());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            }
        }
        //System. out.println("--------------所有任务执行完毕" );
        service.shutdown();
    }
}