Predicates

A predicate is a higher order function that when applied to an element in the stream, returns true if the condition holds, or false otherwise. Predicates can be used for filtering (ex: filtering by currency). Here's an example.

public class BooleanMonetaryAmount {

    public static void main(String[] args) {
        CurrencyUnit dollar = Monetary.getCurrency("USD");
        CurrencyUnit real = Monetary.getCurrency("BRL");


        MonetaryAmount money = Money.of(10, dollar);
        MonetaryAmount money2 = Money.of(10, real);
        MonetaryAmount money3 = Money.of(10, dollar);
        MonetaryAmount money4 = Money.of(9, real);
        MonetaryAmount money5 = Money.of(8, dollar);

        Stream<MonetaryAmount> justDollars = Stream.of(money, money2, money3, money4, money5)
                .filter(MonetaryFunctions.isCurrency(dollar));

        boolean anyMatch = Stream.of(money, money2, money3, money4, money5)
                .anyMatch(MonetaryFunctions.isCurrency(dollar));//true

        boolean allMatch = Stream.of(money, money2, money3, money4, money5)
                .allMatch(MonetaryFunctions.isCurrency(dollar));//true
    }
}