feat: Function composition (#2954)

* feature: Implement Virtual Proxy pattern #2940 * feature: Implement Virtual Proxy pattern #2940 * feature: Implement Virtual Proxy pattern #2940 * feature: Implement Virtual Proxy pattern #2940 * feature: Implement Virtual Proxy pattern #2940 * feature: Implement Virtual Proxy pattern, tests added * feature: Implement Virtual Proxy pattern, tests added * feature: Implement Virtual Proxy pattern, tests added * feature: Implement Virtual Proxy pattern, tests added * feature: Implement Virtual Proxy pattern, tests added * feature: Implement function composition pattern #2897 * task: isolate virtual proxy pattern * task: isolate virtual proxy pattern * refactoring: readme.md
2026-05-14 12:58:37 +00:00 · 2024-06-01 05:26:46 +03:00
parent 68ef414e19
commit 684b2e219e
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+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * 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 NONINFRINGEMENT. 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 com.iluwatar.function.composition;
+
+import java.util.function.Function;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Main application class to demonstrate the use of function composition.
+ */
+public class App {
+
+  /**
+   * Main method to demonstrate function composition using FunctionComposer.
+   *
+   * @param args command line arguments (not used)
+   */
+  public static void main(String[] args) {
+    final var logger = LoggerFactory.getLogger(App.class);
+    Function<Integer, Integer> timesTwo = x -> x * 2;
+    Function<Integer, Integer> square = x -> x * x;
+
+    Function<Integer, Integer> composedFunction = FunctionComposer.composeFunctions(timesTwo, square);
+
+    int result = composedFunction.apply(3);
+    logger.info("Result of composing 'timesTwo' and 'square' functions applied to 3 is: " + result);
+  }
+}
@@ -0,0 +1,46 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * 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 NONINFRINGEMENT. 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 com.iluwatar.function.composition;
+
+import java.util.function.Function;
+
+/**
+ * Class for composing functions using the Function Composition pattern.
+ * Provides a static method to compose two functions using the 'andThen' method.
+ */
+public class FunctionComposer {
+
+  /**
+   * Composes two functions where the output of the first function becomes
+   * the input of the second function.
+   *
+   * @param f1 the first function to apply
+   * @param f2 the second function to apply after the first
+   * @return a composed function that applies f1 and then f2
+   */
+  public static Function<Integer, Integer> composeFunctions(Function<Integer, Integer> f1, Function<Integer, Integer> f2) {
+    return f1.andThen(f2);
+  }
+}
@@ -0,0 +1,40 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * 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 NONINFRINGEMENT. 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 com.iluwatar.function.composition;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+/**
+ * Application test
+ */
+class AppTest {
+
+  @Test
+  void shouldExecuteApplicationWithoutException() {
+    assertDoesNotThrow(() -> App.main(new String[]{}));
+  }
+}
@@ -0,0 +1,102 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * 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 NONINFRINGEMENT. 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 com.iluwatar.function.composition;
+
+import static org.junit.Assert.assertEquals;
+import org.junit.Test;
+import java.util.function.Function;
+
+/**
+ * Test class for FunctionComposer.
+ */
+public class FunctionComposerTest {
+
+  /**
+   * Tests the composition of two functions.
+   */
+  @Test
+  public void testComposeFunctions() {
+    Function<Integer, Integer> timesTwo = x -> x * 2;
+    Function<Integer, Integer> square = x -> x * x;
+
+    Function<Integer, Integer> composed = FunctionComposer.composeFunctions(timesTwo, square);
+
+    assertEquals("Expected output of composed functions is 36", 36, (int) composed.apply(3));
+  }
+
+  /**
+   * Tests function composition with identity function.
+   */
+  @Test
+  public void testComposeWithIdentity() {
+    Function<Integer, Integer> identity = Function.identity();
+    Function<Integer, Integer> timesThree = x -> x * 3;
+
+    Function<Integer, Integer> composedLeft = FunctionComposer.composeFunctions(identity, timesThree);
+    Function<Integer, Integer> composedRight = FunctionComposer.composeFunctions(timesThree, identity);
+
+    assertEquals("Composition with identity on the left should be the same", 9, (int) composedLeft.apply(3));
+    assertEquals("Composition with identity on the right should be the same", 9, (int) composedRight.apply(3));
+  }
+
+  /**
+   * Tests function composition resulting in zero.
+   */
+  @Test
+  public void testComposeToZero() {
+    Function<Integer, Integer> multiply = x -> x * 10;
+    Function<Integer, Integer> toZero = x -> 0;
+
+    Function<Integer, Integer> composed = FunctionComposer.composeFunctions(multiply, toZero);
+
+    assertEquals("Expected output of function composition leading to zero is 0", 0, (int) composed.apply(5));
+  }
+
+  /**
+   * Tests the composition with a negative function.
+   */
+  @Test
+  public void testComposeNegative() {
+    Function<Integer, Integer> negate = x -> -x;
+    Function<Integer, Integer> square = x -> x * x;
+
+    Function<Integer, Integer> composed = FunctionComposer.composeFunctions(negate, square);
+
+    assertEquals("Expected square of negative number to be positive", 9, (int) composed.apply(3));
+  }
+
+  /**
+   * Tests the composition of functions that cancel each other out.
+   */
+  @Test
+  public void testComposeInverseFunctions() {
+    Function<Integer, Integer> timesTwo = x -> x * 2;
+    Function<Integer, Integer> half = x -> x / 2;
+
+    Function<Integer, Integer> composed = FunctionComposer.composeFunctions(timesTwo, half);
+
+    assertEquals("Expect the functions to cancel each other out", 5, (int) composed.apply(5));
+  }
+}