15: Implemented reject method

Author: smithros

readme.md

@@ -28,6 +28,7 @@
     *   [.select](#select)
     *   [.map](#map)
     *   [.count](#count)
+    *   [.reject](#reject)
 
 *   [How to contribute?](#how-to-contribute)
 
@@ -77,6 +78,7 @@ enumerable4j (MIT) | Java 8 | [cactoos](https://github.com/yegor256/cactoos) (MI
 `.any(...)` | `.stream().anyMatch(...);` | `new Or<>(...,...).value()`| tbd |
 `.none(...)` | `.stream().noneMatch(...);` | `new And<>(...,...).value()`| tbd |
 `.select(...)` | `.stream().filter(...).collect(Collectors.toList())` | `new Filtered<>(...,...)` | tbd |
+`.reject(...)` | `.stream().filter((...).negate()).collect(Collectors.toList())` | `new Filtered<>(...,...)` | tbd |
 `.map(...)` | `.stream().map(...).collect(Collectors.toList())` | `new Mapped<>(...,...)` | tbd |
 `.count(...)` | `.stream().filter(...).count()` | `-` | tbd |
 
@@ -108,6 +110,13 @@ Enumerable<Integer> src = new EnumerableOf<>(-1, 1, 2); // [java.util.Collection
 Enumerable<Integer> positive = src.select(v -> v > 0);  // [1, 2] 
 ```
 
+#### .reject
+
+```java
+Enumerable<Integer> src = new EnumerableOf<>(-1, 1, 2); // [java.util.Collection] => [-1, 1, 2]
+Enumerable<Integer> negative = src.reject(v -> v > 0);  // [-1]
+```
+
 #### .map
 
 ```java

src/main/java/io/github/dgroup/enumerable4j/Enumerable.java

@@ -72,6 +72,15 @@ public interface Enumerable<T> extends Collection<T> {
      */
     Enumerable<T> select(Predicate<T> prd);
 
+    /**
+     * Returns an enumerable containing all elements of enumerable for which the given function
+     *  returns a false value.
+     * If no function (null) is given, then 'this' is returned instead.
+     * @param prd The function to match each element.
+     * @return The enumerable.
+     */
+    Enumerable<T> reject(Predicate<T> prd);
+
     /**
      * Returns an enumerable containing all elements, on which given function was applied.
      * If no function (null) is given, then 'this' is returned instead.

src/main/java/io/github/dgroup/enumerable4j/EnumerableOf.java

@@ -100,6 +100,19 @@ public final Enumerable<T> select(final Predicate<T> prd) {
         return out;
     }
 
+    @Override
+    public final Enumerable<T> reject(final Predicate<T> prd) {
+        final Enumerable<T> out;
+        if (prd == null) {
+            out = this;
+        } else {
+            out = new EnumerableOf<>(
+                this.stream().filter(prd.negate()).collect(Collectors.toList())
+            );
+        }
+        return out;
+    }
+
     @Override
     public final <Y> Enumerable<Y> map(final Function<? super T, ? extends Y> fnc) {
         final Enumerable<Y> out;

src/test/java/io/github/dgroup/enumerable4j/RejectTest.java

@@ -0,0 +1,63 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2019-2021 Yurii Dubinka
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom
+ * the Software is  furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE
+ * OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package io.github.dgroup.enumerable4j;
+
+import org.hamcrest.core.AllOf;
+import org.junit.jupiter.api.Test;
+import org.llorllale.cactoos.matchers.Assertion;
+import org.llorllale.cactoos.matchers.HasSize;
+import org.llorllale.cactoos.matchers.HasValues;
+
+/**
+ * Test cases for {@link EnumerableOf#reject}.
+ *
+ * @since 0.1.0
+ * @checkstyle MagicNumberCheck (500 lines)
+ * @checkstyle JavadocMethodCheck (500 lines)
+ */
+@SuppressWarnings("PMD.AvoidDuplicateLiterals")
+final class RejectTest {
+
+    @Test
+    void reject() {
+        new Assertion<>(
+            "Negative values from enumerable found",
+            new EnumerableOf<>(1, 2, 3, -1).reject(val -> val > 0),
+            new AllOf<>(
+                new HasSize(1),
+                new HasValues<>(-1)
+            )
+        ).affirm();
+    }
+
+    @Test
+    void nullFunction() {
+        new Assertion<>(
+            "In case null-function the self enumerable is expected",
+            new EnumerableOf<>(3, 0, 2, -1).select(null),
+            new HasValues<>(3, 0, 2, -1)
+        ).affirm();
+    }
+}