Łukasiewicz predicate logic?

Question

Is there a way to emulate ukasiewicz three-digit logic with the Java API?

More specifically, I want to imitate Łukasiewicz ' "M" ("this is not a lie ...") .

For example, I need to build this Predicate<String>one that gives the following results:

predicate.test("0") = false
predicate.test(null) = true
predicate.test("1") = true

which, when denied, gives:

predicate.negate().test("0") = true
predicate.negate().test(null) = true
predicate.negate().test("1") = false

If the value is for the test A, my predicate calculates MA. What it negate()does is compute ¬MA, while I want it to compute M¬A.

PS Do not bother developing a three-digit replacement answer with a three- Predicatedigit replacement boolean, because I know quite well how to do it myself. I ask this question to find out if this is possible with pure Java8 with minimal extra coding effort.

Answer 1

Looks like this is what you want:

static <T> Predicate<T> p(Predicate<? super T> o){ //(I'm not sure what to name this)
    return new Predicate<T>(){
        @Override
        public boolean test(T t) {
            return t == null || o.test(t);
        }
        @Override
        public Predicate<T> negate(){
            return p(o.negate());
        }
    };
}
....
Predicate<String> predicate = p(t -> !"0".equals(t));

If the value for the test is null, we return true, otherwise we will use the original predicate. To deny, we simply deny the original predicate.

---

If null is not always the third value you could pass in another predicate to check for this:

static <T> Predicate<T> p(Predicate<? super T> isUnknown, Predicate<? super T> isTrue){
    return new Predicate<T>(){
        @Override
        public boolean test(T t) {
            return isUnknown.test(t) || isTrue.test(t);
        }
        @Override
        public Predicate<T> negate(){
            return p(isUnknown, isTrue.negate());
        }
    };
}

Answer 2

, negate() Predicate: , , . , , predicate.test(null) predicate.negate().test(null) true.

. negate boolean. trueValue falseValue. thirdValue true. , , t210 > ( , ).

public static void main(String... args) {
    Predicate<String> predicate = lukasiewicz("1", "0", null);

    System.out.println(predicate.test("0"));
    System.out.println(predicate.test(null));
    System.out.println(predicate.test("1"));

    System.out.println(predicate.negate().test("0"));
    System.out.println(predicate.negate().test(null));
    System.out.println(predicate.negate().test("1"));
}

private static <T> Predicate<T> lukasiewicz(T trueValue, T falseValue, T thirdValue) {
    class LukasiewiczPredicate implements Predicate<T> {

        private boolean negate; 

        private LukasiewiczPredicate(boolean negate) {
            this.negate = negate;
        }

        @Override
        public boolean test(T t) {
            if (Objects.equals(trueValue, t)) return negate;
            if (Objects.equals(falseValue, t)) return !negate;
            if (Objects.equals(thirdValue, t)) return true;
            return false;
        }

        @Override
        public Predicate<T> negate() {
            return new LukasiewiczPredicate(!negate);
        }

    };
    return new LukasiewiczPredicate(true);
}