feat: Add andThen and compose to japi function (#2147)

* feat: Add andThen and compose to japi function

* Update actor/src/main/scala/org/apache/pekko/japi/function/Function.scala

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update actor/src/main/scala/org/apache/pekko/japi/function/Function.scala

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update actor/src/main/scala/org/apache/pekko/japi/function/Function.scala

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update actor/src/main/scala/org/apache/pekko/japi/function/Function.scala

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* .

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

actor-tests/src/test/java/org/apache/pekko/japi/FunctionLawTest.java

@@ -0,0 +1,72 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.pekko.japi;
+
+import org.apache.pekko.japi.function.Function;
+import org.apache.pekko.japi.function.Function2;
+import org.apache.pekko.japi.function.Predicate;
+import org.apache.pekko.japi.function.Predicate2;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class FunctionLawTest {
+
+  @Test
+  public void testFunctionCompose() throws Exception {
+    Function<Long, Long> f = v1 -> v1 + 1;
+    Function<Long, Long> g = v1 -> v1 * 2;
+    Function<Long, Long> h = f.compose(g);
+    Assert.assertEquals(5L, h.apply(2L).longValue());
+    Assert.assertEquals(6L, g.compose(f).apply(2L).longValue());
+  }
+
+  @Test
+  public void testFunctionAndThen() throws Exception {
+    Function<Long, Long> f = v1 -> v1 + 1;
+    Function<Long, Long> g = v1 -> v1 * 2;
+    Function<Long, Long> h = f.andThen(g);
+    Assert.assertEquals(6L, h.apply(2L).longValue());
+    Assert.assertEquals(5L, g.andThen(f).apply(2L).longValue());
+  }
+
+  @Test
+  public void testFunction2AndThen() throws Exception {
+    Function2<Long, Long, Long> f = Long::sum;
+    Function<Long, Long> g = v1 -> v1 * 2;
+    Function2<Long, Long, Long> h = f.andThen(g);
+    Assert.assertEquals(10L, h.apply(2L, 3L).longValue());
+  }
+
+  @Test
+  public void testPredicateNegate() {
+    final Predicate<Object> alwaysTrue = o -> true;
+    final Predicate<Object> alwaysFalse = alwaysTrue.negate();
+    Assert.assertTrue(alwaysTrue.test(new Object()));
+    Assert.assertFalse(alwaysFalse.test(new Object()));
+    Assert.assertTrue(alwaysTrue.negate().negate().test(new Object()));
+  }
+
+  @Test
+  public void testPredicate2Negate() {
+    final Predicate2<Object, Object> alwaysTrue = (o1, o2) -> true;
+    final Predicate2<Object, Object> alwaysFalse = alwaysTrue.negate();
+    Assert.assertTrue(alwaysTrue.test(new Object(), new Object()));
+    Assert.assertFalse(alwaysFalse.test(new Object(), new Object()));
+    Assert.assertTrue(alwaysTrue.negate().negate().test(new Object(), new Object()));
+  }
+}

actor/src/main/scala/org/apache/pekko/japi/function/Function.scala

@@ -28,6 +28,18 @@ import scala.annotation.nowarn
 trait Function[-T, +R] extends java.io.Serializable {
   @throws(classOf[Exception])
   def apply(param: T): R
+
+  /**
+   * That is, the resulting function is equivalent to `this(g(v))`.
+   * @since 2.0.0
+   */
+  def compose[V](g: Function[V, T]): Function[V, R] = (v: V) => this.apply(g.apply(v))
+
+  /**
+   * Creates a composed function that first applies this function to its input, then applies `g` to the result.
+   * @since 2.0.0
+   */
+  def andThen[V](g: Function[R, V]): Function[T, V] = (t: T) => g.apply(this.apply(t))
 }
 
 object Function {
@@ -50,6 +62,16 @@ object Function {
 trait Function2[-T1, -T2, +R] extends java.io.Serializable {
   @throws(classOf[Exception])
   def apply(arg1: T1, arg2: T2): R
+
+  /**
+   * Compose this function with another function `g`, such that the resulting function
+   * is equivalent to `g(this(x1, x2))`.
+   * This creates a composed function that first applies this function to its arguments,
+   * and then applies function `g` to the result.
+   * @since 2.0.0
+   */
+  def andThen[V](g: Function[R, V]): Function2[T1, T2, V] =
+    (t1: T1, t2: T2) => g.apply(this.apply(t1, t2))
 }
 
 /**
@@ -89,6 +111,12 @@ trait Effect extends java.io.Serializable {
 @FunctionalInterface
 trait Predicate[-T] extends java.io.Serializable {
   def test(param: T): Boolean
+
+  /**
+   * Returns a predicate that represents the logical negation of this predicate.
+   * @since 2.0.0
+   */
+  def negate: Predicate[T] = (t: T) => !this.test(t)
 }
 
 /**
@@ -101,6 +129,12 @@ trait Predicate[-T] extends java.io.Serializable {
 @FunctionalInterface
 trait Predicate2[-T1, -T2] extends java.io.Serializable {
   def test(param1: T1, param2: T2): Boolean
+
+  /**
+   * Returns a predicate that represents the logical negation of this predicate.
+   * @since 2.0.0
+   */
+  def negate: Predicate2[T1, T2] = (t1: T1, t2: T2) => !this.test(t1, t2)
 }
 
 /**