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/*
* Copyright (C) Posten Norge AS
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package no.digipost;
import java.util.concurrent.atomic.AtomicLong;
import java.util.function.Predicate;
public final class DiggPredicates {
/**
* Create a new predicate which only yields true on the nth
* {@code true}-yielding invocation of a given predicate.
*
*
* As this is a stateful predicate, it should usually not be kept as a
* reference, but used inline when processing a number of elements,
* with {@link java.util.stream.Stream#filter streams}.
*
* @param n the nth {@code true}-yielding invocation, {@code 1} indicates first,
* {@code 2} second, and so forth. {@code 0} or less will throw an
* {@code IllegalArgumentException}.
* @param predicate the predicate.
* @return the new predicate.
*/
public static Predicate nth(long n, Predicate predicate) {
if (n <= 0) {
throw new IllegalArgumentException(n + " is not a valid number for n. It must be 1 or greater");
}
AtomicLong foundMatches = new AtomicLong();
return t -> predicate.test(t) && foundMatches.incrementAndGet() == n;
}
private DiggPredicates() {}
}