import java.util.*;
import java.util.stream.Collectors; 

public class HigherOrder {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<Integer>();
        numbers.add(5);
        numbers.add(9);
        numbers.add(8);
        numbers.add(1);
        
        // the forEach function takes a lambda function and does it on all of the items
        numbers.forEach(n -> {System.out.println(n);});
        System.out.println();

        // the map function works on a "Stream" object, not a list directly
        // it also returns a stream, which can be forEach'd
        numbers.stream().map(n -> n * n).forEach(n -> {System.out.println(n);});
        System.out.println();

        // reduce is the same thing as fold
        int result = numbers.stream().reduce(0, (a, b) -> a + b);
        System.out.println("Sum = " + result);
        
        result = numbers.stream().reduce(1, (a, b) -> a * b);
        System.out.println("Product = " + result + "\n");
    
        // filter exists on streams as well
        numbers.stream().filter(x -> x % 2 == 0).forEach(n -> {System.out.println(n);});
    }
}