多个线程同时运行，顺序打印问题

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输入一串字符串；开启三个线程；分别在输入的字符串后面打印  "_A"   "_B"  "_C" 输出结果。

输入：hello

输出：hello_A_B_C

思路：使用Callable 可以返回对应的打印，再在原字符串的基础上拼接。

1）使用join

2）使用线程池里的SingleThreadPool

第一种方法：

import java.util.Scanner;
import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;

public class Main1 {
    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNextLine()) {
            String string = scanner.nextLine();
            FutureTask<String> futureTask1 = new FutureTask<>((Callable<String>) () -> {
                try {

                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    return "_A";
                }

            });
            FutureTask<String> futureTask2 = new FutureTask<String>((Callable<String>) () -> {
                try {


                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    return "_B";
                }

            });
            FutureTask<String> futureTask3 = new FutureTask<String>((Callable<String>) () -> {
                try {

                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    return "_C";
                }

            });

            Thread t1 = new Thread(futureTask1);
            Thread t2 = new Thread(futureTask2);
            Thread t3 = new Thread(futureTask3);

            t1.start();
            t2.start();
            t3.start();

            t1.join();
            t2.join();
            t3.join();

            string += futureTask1.get();
            string += futureTask2.get();
            string += futureTask3.get();

            System.out.println(string);

        }
    }
}

第二种方法：

import java.util.Scanner;
import java.util.concurrent.*;

class main{

    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        while(scanner.hasNextLine()){
            String string = scanner.nextLine();
            //CountDownLatch countDownLatch = new CountDownLatch(3);
            FutureTask<String> task1 = new FutureTask<>((Callable<String>)()->{
                try{

                }catch (Exception e){
                    e.printStackTrace();
                }finally {
                    //countDownLatch.countDown();
                    return "_A";
                }

            });
            FutureTask<String> task2 = new FutureTask<>((Callable<String>)()->{
                try{

                }catch (Exception e){
                    e.printStackTrace();
                }finally {
                    //countDownLatch.countDown();
                    return "_B";
                }
            });
            FutureTask<String> task3 = new FutureTask<>((Callable<String>)()->{
                try{

                }catch (Exception e){
                    e.printStackTrace();
                }finally {
                    //countDownLatch.countDown();
                    return "_C";
                }
            });

            ExecutorService executorService = Executors.newSingleThreadExecutor();

            executorService.submit(task1);
            executorService.submit(task2);
            executorService.submit(task3);

            string += task1.get();
            string += task2.get();
            string += task3.get();


            //countDownLatch.await();
            System.out.println(string);
        }
    }
}