java : reduce stream of list of maps

package homeWork;
import java.math.BigDecimal;

import java.util.ArrayList;

import java.util.Comparator;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import java.util.stream.Collectors;
public class sumSample {


	public static void main(String[] args) {

		

		List> countries = new ArrayList>();

		Map country;

		country = new HashMap();

		country.put( "name",       "japan" );

		country.put( "currency",   "JPY" );

		country.put( "population", new BigDecimal("127156000"));

		countries.add( country );
		country = new HashMap();

		country.put( "name", "france" );

		country.put( "currency", "EUR" );

		country.put( "population", new BigDecimal("65073482"));

		countries.add( country );

		

		country = new HashMap();

		country.put( "name",       "japan" );

		country.put( "currency",   "JPY" );

		country.put( "population", new BigDecimal("56000"));

		countries.add( country );
		country = new HashMap();

		country.put( "name", "spain" );

		country.put( "currency", "EUR" );

		country.put( "population", new BigDecimal("44904000"));

		countries.add( country );
		country = new HashMap();

		country.put( "name", "russia" );

		country.put( "currency", "RUB" );

		country.put( "population", new BigDecimal("141903979") );

		countries.add( country );

		

		for(Mapct:countries) {

			System.out.println(ct.get("name")+":"+ct.get("population"));

		}

		System.out.println("-----------------------");

	

		BigDecimal totalBg=BigDecimal.ZERO;

		totalBg = countries.stream().map(m -> ((BigDecimal) m.get("population"))).reduce(BigDecimal.ZERO, BigDecimal::add);		

		System.out.println("sum: "+totalBg.toString());

	}	

}
result:
japan:127156000

france:65073482

japan:56000

spain:44904000

russia:141903979












































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sum: 379093461