What does the following Java code demonstrate?

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class Main {
    public static void main(String[] args) {
        List<Integer> numbers = new ArrayList<>();
        numbers.add(3);
        numbers.add(1);
        numbers.add(2);
        Collections.sort(numbers);
        System.out.println(numbers.get(0));
    }
}