CODEWITHSUNDEEP
javacollectionsjava-stream
Erick Dunstov
Erick Dunstov

Reputation: 21

How to filter my List with Strings?

Could someone explain me why I can`t filter my strings in List by .stream().filter ? All I receive is unfiltered strings! I will appreciate it.

public static void main(String[] args) throws FileNotFoundException {

        List<Country> countries = CsvToBeanConverterCountry("country.csv");
        countries
                .stream().filter(s -> s.getName().contains("xx")).collect(Collectors.toList());
        countries.forEach(s -> System.out.println(s.getName()));
    }

    private static List CsvToBeanConverterCountry(String csvFilename) throws FileNotFoundException {

        CsvToBean csv = new CsvToBean();
        CSVReader csvReader = new CSVReader(new FileReader(csvFilename), ';', '"', 1);
        List list = csv.parse(setColumMappingCountry(), csvReader);
        return list;
    }

    private static ColumnPositionMappingStrategy setColumMappingCountry() {
        ColumnPositionMappingStrategy strategy = new ColumnPositionMappingStrategy();
        strategy.setType(Country.class);
        String[] columns = new String[]{"country_id", "city_id", "name"};
        strategy.setColumnMapping(columns);
        return strategy;
    }
}

Upvotes: 2

Views: 126

Answers (4)

erickson
erickson

Reputation: 269867

It seems like your intent was to modify the original list, rather than to produce a new list with some of the elements.

In that case, you can simply remove the elements you don't want:

countries.removeIf(c -> !c.getName().contains("xx"));

This is more efficient than creating a stream and a new collection, but it alters the list.

Upvotes: 2

Brother
Brother

Reputation: 2220

Sure, what happens is that: .stream() doesn't change the actual list.

What you can do is:

List<Country> countries = CsvToBeanConverterCountry("country.csv");
countries
    .stream()
    .filter(s -> s.getName().contains("xx"))
    .forEach(s -> System.out.println(s.getName()));

Upvotes: 1

Mạnh Quyết Nguyễn
Mạnh Quyết Nguyễn

Reputation: 18235

You ignored the result of collect:

countries.stream().filter(s -> s.getName().contains("xx"))
         .collect(Collectors.toList());

So you should assign the result to a new list and print that list only

List<Country> result = countries.stream()...
result.forEach(...)

Upvotes: 7

ernest_k
ernest_k

Reputation: 45339

You should assign the result to countries:

countries = countries.stream().filter(s -> s.getName()
             .contains("xx")).collect(Collectors.toList());
countries.forEach(s -> System.out.println(s.getName()));

countries.stream().filter(...) does not filter the countries list inline, it runs a stream and the result is ignored.

Also, you can run forEach on the stream directly without collecting into a list first:

countries.stream().filter(s -> s.getName()
             .contains("xx"))
             .forEach(s -> System.out.println(s.getName()));

Upvotes: 3

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