jdk/src/share/classes/java/util/function/Predicate.java

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package java.util.function;

import java.util.Objects;

/**
 * Determines if the input object matches some criteria.
 *
 * @param <T> the type of argument to {@code test}
 *
 * @since 1.8
 */
@FunctionalInterface
public interface Predicate<T> {

    /**
     * Returns {@code true} if the input object matches some criteria.
     *
     * @param t the input object
     * @return {@code true} if the input object matches some criteria, otherwise
     * {@code false}
     */
    boolean test(T t);

    /**
     * Returns a predicate which evaluates to {@code true} only if this
     * predicate and the provided predicate both evaluate to {@code true}. If
     * this predicate returns {@code false} then the remaining predicate is not
     * evaluated.
     *
     * <p>Any exceptions thrown by either {@code test} method are relayed
     * to the caller; if performing first operation throws an exception, the
     * second operation will not be performed.
     *
     * @param p a predicate which will be logically-ANDed with this predicate
     * @return a new predicate which returns {@code true} only if both
     * predicates return {@code true}
     * @throws NullPointerException if p is null
     */
    default Predicate<T> and(Predicate<? super T> p) {
        Objects.requireNonNull(p);
        return (t) -> test(t) && p.test(t);
    }

    /**
     * Returns a predicate which negates the result of this predicate.
     *
     * @return a new predicate who's result is always the opposite of this
     * predicate.
     */
    default Predicate<T> negate() {
        return (t) -> !test(t);
    }

    /**
     * Returns a predicate which evaluates to {@code true} if either this
     * predicate or the provided predicate evaluates to {@code true}. If this
     * predicate returns {@code true} then the remaining predicate is not
     * evaluated.
     *
     * <p>Any exceptions thrown by either {@code test} method are relayed
     * to the caller; if performing first operation throws an exception, the
     * second operation will not be performed.
     *
     * @param p a predicate which will be logically-ORed with this predicate
     * @return a new predicate which returns {@code true} if either predicate
     * returns {@code true}
     * @throws NullPointerException if p is null
     */
    default Predicate<T> or(Predicate<? super T> p) {
        Objects.requireNonNull(p);
        return (t) -> test(t) || p.test(t);
    }

    /**
     * Returns a predicate who's result matches
     * {@code Objects.equals(target, t)}.
     *
     * @param <T> the type of values evaluated by the predicate
     * @param target the target value to be compared for equality
     * @return a predicate who's result matches
     * {@code Objects.equals(target, t)}
     */
    static <T> Predicate<T> isEqual(Object target) {
        return (null == target)
                ? Objects::isNull
                : object -> target.equals(object);
    }
}