Java collections

Java collection

  // Convert List to Set
  List<String> numbers1 = Arrays.asList("1", "2", "3", "4", "5", "6");
  System.out.println("Output1:" + numbers1.toString());

  Set<String> numbers2 = numbers.stream().collect(Collectors.toSet());
  System.out.println("Output2:" + numbers2.toString());

Output1:[1, 2, 3, 4, 5, 6]
Output2:[1, 2, 3, 4, 5, 6]

Example of stream, map, filter and collect

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class ListTest {
    public static void main(String args[]) {
        List<String> numbers = Arrays.asList("1", "2", "3", "4", "5", "6");
        System.out.println("original list: " + numbers);

        List<Integer> even = numbers.stream()
                .map(s -> Integer.valueOf(s))
                .filter(number -> number % 2 == 0)
                .collect(Collectors.toList());

        System.out.println("processed list, only even numbers: " + even);
    }
}

Result:

original list: [1, 2, 3, 4, 5, 6]
processed list, only even numbers: [2, 4, 6]