8050818: Predicate::not - provide an easier way to negate a predicate
Reviewed-by: chegar, dl, psandoz, forax, smarks, redestad
--- a/src/java.base/share/classes/java/util/function/Predicate.java Wed May 30 17:30:06 2018 +0200
+++ b/src/java.base/share/classes/java/util/function/Predicate.java Wed May 30 12:40:04 2018 -0300
@@ -116,4 +116,20 @@
? Objects::isNull
: object -> targetRef.equals(object);
}
+
+ /**
+ * 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
+ */
+ @SuppressWarnings("unchecked")
+ static <T> Predicate<T> not(Predicate<? super T> target) {
+ return (Predicate<T>)target.negate();
+ }
}
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/test/jdk/java/util/function/PredicateNotTest.java Wed May 30 12:40:04 2018 -0300
@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8050818
+ * @run testng PredicateNotTest
+ */
+
+import java.util.List;
+import java.util.function.Predicate;
+import org.testng.annotations.Test;
+import static java.util.function.Predicate.not;
+import static java.util.stream.Collectors.joining;
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.fail;
+
+@Test(groups = "unit")
+public class PredicateNotTest {
+ static class IsEmptyPredicate implements Predicate<String> {
+ @Override
+ public boolean test(String s) {
+ return s.isEmpty();
+ }
+ }
+
+ public void test() {
+ List<String> test = List.of(
+ "A non-empty line",
+ "",
+ "A non-empty line",
+ "",
+ "A non-empty line",
+ "",
+ "A non-empty line",
+ ""
+ );
+ String expected = "A non-empty line\nA non-empty line\nA non-empty line\nA non-empty line";
+
+ assertEquals(test.stream().filter(not(String::isEmpty)).collect(joining("\n")), expected);
+ assertEquals(test.stream().filter(not(s -> s.isEmpty())).collect(joining("\n")), expected);
+ assertEquals(test.stream().filter(not(new IsEmptyPredicate())).collect(joining("\n")), expected);
+ assertEquals(test.stream().filter(not(not(not(String::isEmpty)))).collect(joining("\n")), expected);
+ assertEquals(test.stream().filter(not(not(not(s -> s.isEmpty())))).collect(joining("\n")), expected);
+ assertEquals(test.stream().filter(not(not(not(new IsEmptyPredicate())))).collect(joining("\n")), expected);
+ }
+}
+