java11-predicate

The main goal of this project is to show updated Predicate Interface
from Java 11.

overview

• and: returns a composed predicate that represents a short-circuiting
  logical AND of this predicate and another

    default Predicate<T> and(Predicate<? super T> other) {
        Objects.requireNonNull(other);
        return (t) -> test(t) && other.test(t);
    }

• negate: returns a predicate that represents the logical negation
  of this predicate

    default Predicate<T> negate() {
            return (t) -> !test(t);
        }

• or: returns a composed predicate that represents a short-circuiting
  logical OR of this predicate and another

    default Predicate<T> or(Predicate<? super T> other) {
        Objects.requireNonNull(other);
        return (t) -> test(t) || other.test(t);
    }

• isEqual: returns a predicate that tests if two arguments are equal
  according to Objects.equals(Object, Object)

    static <T> Predicate<T> isEqual(Object targetRef) {
        return (null == targetRef)
                ? Objects::isNull
                : object -> targetRef.equals(object);
    }

• not: returns a predicate that is the negation of the supplied
  predicate

    static <T> Predicate<T> not(Predicate<? super T> target) {
        Objects.requireNonNull(target);
        return (Predicate<T>)target.negate();
    }

best practices

Suppose that we want to filter Stream of objects by some field

class X {
    String value;
    // constructors, getters...
}

• naive approach

    List<X> filtered = xes.stream()
            .filter(x -> Objects.equals(x.value, "test"))
            .collect(Collectors.toList());

• better approach
  1. define static method in X

      static Predicate<X> byValue(String value) {
          return x -> nonNull(x) && Objects.equals(x.value, value);
      }

  2. construct pipeline

      List<X> filtered = xes.stream()
              .filter(X.byValue("test1"))
              .collect(Collectors.toList());

  3. easy to compose

      var filtered = xes.stream()
              .filter(X.byValue("test1").or(X.byValue("test2")))
              .collect(Collectors.toList());