Summary

Introduce a new static method Predicate::not which will allow developers to negate predicate lambdas trivially.

Problem

The requirement for predicate negation occurs frequently since predicates are defined antipodal to a positive selection; isNull, isEmpty, isBlank.

Presently there is no easy way to negate a predicate lambda without first wrapping in a Predicate Object.

Ex.

    List<String> list = bufferedReader
      .lines()
      .filter(((Predicate<String>)String::isEmpty).negate())
      .collect(toList()); 

Solution

Introduce a method that accepts an unwrapped lambda and returns the negated form.

Ex.

import static java.util.function.Predicate.not;
...

    List<String> list = bufferedReader
      .lines()
      .filter(not(String::isEmpty))
      .collect(toList()); 

Specification

    /**
     * Returns a predicate that is the negation of the
     * supplied predicate.
     * @param <T>     the type of arguments to the
     *                specified predicate
     * @param target  predicate to negate
     *
     * @return a predicate that negates the results
     *         of the supplied predicate
     *
     * @since 11
     */
    static <T> Predicate<T> not(Predicate<? super T> target) {
        return (Predicate<T>)target.negate();
    }