您没有公开足够的代码来解决您的特定问题。但这里有一些提示和一些示例代码。
我对这方面不在行 Scanner ，但似乎你应该 … s.next(); 而不是 … s.nextLine(); .
总是在应用程序结束前关闭executor服务。否则，后台线程池可能会无限期地继续，就像僵尸一样？‍♂️.
使用现代java可以缩短代码。例如 Map.of , switch 表达式，并尝试使用资源。新的 record feature在合成getter时为不可变对象定义一个类， toString , equals ，和 hashCode 方法。但这只是语法，概念与原始代码中的相同。
通常最好从输入中去掉空白。
添加 default 给你的 switch 捕捉意外输入。
这里是一个完整的工作示例应用程序与代码接近您的原始。

package work.basil.example;

import java.util.*;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class MapOut
{
    public static void main ( String[] args )
    {
        MapOut app = new MapOut();
        app.demo();
    }

    private void demo ( )
    {
        // ----------|  Data  |------------------------------------------
        record City( String name , String code )
        {
        }

        Map < String , City > map = Map.of(
                "MOW" , new City( "Moscow" , "MOW" ) ,
                "LON" , new City( "London" , "LON" ) ,
                "NYC" , new City( "New York" , "NYC" ) ,
                "BER" , new City( "Berlin" , "BER" ) ,
                "DEL" , new City( "New Delhi" , "DEL" )
        );
        System.out.println( "map = " + map );

        // ----------|  Action  |------------------------------------------
        ExecutorService executorService = null;
        try (
                Scanner scanner = new Scanner( System.in ) ;
        )
        {
            executorService = Executors.newFixedThreadPool( 5 );

            for ( String key : map.keySet() )
            {
                City city = map.get( key );
                System.out.println( "City code: " + city.code + " | name: " + city.name );
            }
            System.out.println( "Select a minimum of three and a maximum of five cities listed above. First of all, please specify the number of cities you will choose: " );
            int length = scanner.nextInt();
            System.out.println( "Please enter " + length + " city codes, pressing Return/Enter after each: " );
            List < String > inputCodes = new ArrayList <>( length );
            for ( int i = 0 ; i < length ; i++ )
            {
                String input = scanner.next();
                inputCodes.add( input.strip().trim() );
            }

            for ( String inputCode : inputCodes )
            {
                switch ( inputCode )
                {
                    case "MOW" -> executorService.submit( ( ) -> System.out.println( map.get( inputCode ).name ) );
                    case "LON" -> executorService.submit( ( ) -> System.out.println( map.get( inputCode ).name ) );
                    case "NYC" -> executorService.submit( ( ) -> System.out.println( map.get( inputCode ).name ) );
                    case "BER" -> executorService.submit( ( ) -> System.out.println( map.get( inputCode ).name ) );
                    case "DEL" -> executorService.submit( ( ) -> System.out.println( map.get( inputCode ).name ) );
                    default -> throw new IllegalStateException( "Expected city code: " + inputCode );
                }
            }
        }
        finally
        {
            if ( Objects.nonNull( executorService ) )
            {
                executorService.shutdown(); // Always shutdown your executor service. Otherwise it may continue indefinitely, like a zombie ?‍.
            }
        }
    }
}

正如目前所写的那样，做一个 switch 输入代码。我们可以放下枪 switch 用一条线 executorService.submit( ( ) -> System.out.println( map.get( inputCode ).name ) ); . 但我假设你脑子里还有其他特定于代码的逻辑，所以我把它忘了 switch 到位。
运行时，用户输入： 2 , MOW ，和 LON .

map = {MOW=City[name=Moscow, code=MOW], LON=City[name=London, code=LON], NYC=City[name=New York, code=NYC], DEL=City[name=New Delhi, code=DEL], BER=City[name=Berlin, code=BER]}
City code: MOW | name: Moscow
City code: LON | name: London
City code: NYC | name: New York
City code: DEL | name: New Delhi
City code: BER | name: Berlin
Select a minimum of three and a maximum of five cities listed above. First of all, please specify the number of cities you will choose: 
2
Please enter 2 city codes, pressing Return/Enter after each: 
MOW
LON
Moscow
London