Adding source code for article tracked under BAEL-4576 (#10203)

Co-authored-by: CHANDRAKANT Kumar <kumar.chandrakant@soprabanking.com>

core-java-modules/core-java-functional/README.md

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+## Relevant articles:

core-java-modules/core-java-functional/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project
+    xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-functional</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-functional</name>
+    <packaging>jar</packaging>
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../</relativePath>
+    </parent>
+
+</project>

core-java-modules/core-java-functional/src/main/java/com/baeldung/functional/Currying.java

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+package com.baeldung.functional;
+
+import java.util.function.Function;
+
+public class Currying {
+
+    private static Function<Double, Function<Double, Double>> weight = mass -> gravity -> mass * gravity;
+
+    private static Function<Double, Double> weightOnEarth = weight.apply(9.81);
+
+    private static Function<Double, Double> weightOnMars = weight.apply(3.75);
+
+    public static Double weightOnEarth(Double mass) {
+        return weightOnEarth.apply(mass);
+    }
+
+    public static Double weightOnMars(Double mass) {
+        return weightOnMars.apply(mass);
+    }
+
+    public static Function<Double, Double> weightOnEarth() {
+        final double gravity = 9.81;
+        return mass -> mass * gravity;
+    }
+
+}

core-java-modules/core-java-functional/src/main/java/com/baeldung/functional/FirstClassFunctions.java

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+package com.baeldung.functional;
+
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+
+public class FirstClassFunctions {
+
+    public static List<Integer> sortWithoutLambda(List<Integer> numbers) {
+        Collections.sort(numbers, new Comparator<Integer>() {
+            @Override
+            public int compare(Integer n1, Integer n2) {
+                return n1.compareTo(n2);
+            }
+        });
+        return numbers;
+    }
+
+    public static List<Integer> sortWithLambda(List<Integer> numbers) {
+        Collections.sort(numbers, (n1, n2) -> n1.compareTo(n2));
+        return numbers;
+    }
+
+}

core-java-modules/core-java-functional/src/main/java/com/baeldung/functional/FunctionComposition.java

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+package com.baeldung.functional;
+
+import java.util.function.Function;
+
+public class FunctionComposition {
+
+    private static Function<Double, Double> log = (value) -> Math.log(value);
+    private static Function<Double, Double> sqrt = (value) -> Math.sqrt(value);
+
+    public static Double logThenSqrt(Double number) {
+        Function<Double, Double> logThenSqrt = sqrt.compose(log);
+        return (logThenSqrt.apply(3.14));
+    }
+
+    public static Double sqrtThenLog(Double number) {
+        Function<Double, Double> sqrtThenLog = sqrt.andThen(log);
+        return (sqrtThenLog.apply(3.14));
+    }
+
+}

core-java-modules/core-java-functional/src/main/java/com/baeldung/functional/ImmutableData.java

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+package com.baeldung.functional;
+
+public class ImmutableData {
+
+    private final String someData;
+
+    private final AnotherImmutableData anotherImmutableData;
+
+    public ImmutableData(final String someData, final AnotherImmutableData anotherImmutableData) {
+        this.someData = someData;
+        this.anotherImmutableData = anotherImmutableData;
+    }
+
+    public String getSomeData() {
+        return someData;
+    }
+
+    public AnotherImmutableData getAnotherImmutableData() {
+        return anotherImmutableData;
+    }
+
+    public class AnotherImmutableData {
+
+        private final Integer someOtherData;
+
+        public AnotherImmutableData(final Integer someData) {
+            this.someOtherData = someData;
+        }
+
+        public Integer getSomeOtherData() {
+            return someOtherData;
+        }
+
+    }
+
+}

core-java-modules/core-java-functional/src/main/java/com/baeldung/functional/Monads.java

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+package com.baeldung.functional;
+
+import java.util.Optional;
+
+public class Monads {
+
+    public static Optional<Integer> add(Optional<Integer> val1, Optional<Integer> val2) {
+        return val1.flatMap(first -> val2.flatMap(second -> Optional.of(first + second)));
+    }
+
+}

core-java-modules/core-java-functional/src/main/java/com/baeldung/functional/PureFunctions.java

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+package com.baeldung.functional;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class PureFunctions {
+
+    public static Integer sum(List<Integer> numbers) {
+        return numbers.stream()
+            .collect(Collectors.summingInt(Integer::intValue));
+    }
+
+}

core-java-modules/core-java-functional/src/main/java/com/baeldung/functional/Recursion.java

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+package com.baeldung.functional;
+
+public class Recursion {
+
+    public static Integer headRecursion(Integer number) {
+
+        return (number == 1) ? 1 : number * headRecursion(number - 1);
+
+    }
+
+    public static Integer tailRecursion(Integer number, Integer result) {
+
+        return (number == 1) ? result : tailRecursion(number - 1, result * number);
+
+    }
+
+}

core-java-modules/core-java-functional/src/main/java/com/baeldung/functional/ReferentialTransparency.java

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+package com.baeldung.functional;
+
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public class ReferentialTransparency {
+
+    private static Logger logger = Logger.getGlobal();
+
+    public void main() {
+
+        String data = new SimpleData().setData("Baeldung")
+            .getData();
+        logger.log(Level.INFO, new SimpleData().setData("Baeldung")
+            .getData());
+        logger.log(Level.INFO, data);
+        logger.log(Level.INFO, "Baeldung");
+    }
+
+    public class SimpleData {
+
+        private Logger logger = Logger.getGlobal();
+
+        private String data;
+
+        public String getData() {
+            logger.log(Level.INFO, "Get data called for SimpleData");
+            return data;
+        }
+
+        public SimpleData setData(String data) {
+            logger.log(Level.INFO, "Set data called for SimpleData");
+            this.data = data;
+            return this;
+        }
+
+    }
+
+}

core-java-modules/core-java-functional/src/test/java/com/baeldung/functional/CurryingUnitTest.java

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+package com.baeldung.functional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.Test;
+
+public class CurryingUnitTest {
+
+    @Test
+    public void testWeightOnEarth() {
+
+        assertEquals(588.6, Currying.weightOnEarth(60.0), 0.1);
+
+    }
+
+    @Test
+    public void testWeightOnMars() {
+
+        assertEquals(225.0, Currying.weightOnMars(60.0), 0.1);
+
+    }
+}

core-java-modules/core-java-functional/src/test/java/com/baeldung/functional/FirstClassFunctionsUnitTest.java

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+package com.baeldung.functional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Arrays;
+
+import org.junit.Test;
+
+public class FirstClassFunctionsUnitTest {
+
+    @Test
+    public void testSortingWithoutLambda() {
+
+        assertEquals(new Integer(8), FirstClassFunctions.sortWithoutLambda(Arrays.asList(new Integer(10), new Integer(8)))
+            .get(0));
+
+    }
+
+    @Test
+    public void testSortingWithLambda() {
+
+        assertEquals(new Integer(8), FirstClassFunctions.sortWithLambda(Arrays.asList(new Integer(10), new Integer(8)))
+            .get(0));
+
+    }
+
+}

core-java-modules/core-java-functional/src/test/java/com/baeldung/functional/FunctionCompositionUnitTest.java

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+package com.baeldung.functional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.Test;
+
+public class FunctionCompositionUnitTest {
+
+    @Test
+    public void testLogThenSqrt() {
+
+        assertEquals(1.07, FunctionComposition.logThenSqrt(3.14), 0.01);
+
+    }
+
+    @Test
+    public void testSqrtThenLog() {
+
+        assertEquals(0.57, FunctionComposition.sqrtThenLog(3.14), 0.01);
+
+    }
+
+}

core-java-modules/core-java-functional/src/test/java/com/baeldung/functional/MonadsUnitTest.java

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+package com.baeldung.functional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Optional;
+
+import org.junit.Test;
+
+public class MonadsUnitTest {
+
+    @Test
+    public void testOptionalAdd() {
+
+        assertEquals(5, Monads.add(Optional.of(new Integer(2)), Optional.of(new Integer(3)))
+            .get());
+
+    }
+
+}

core-java-modules/core-java-functional/src/test/java/com/baeldung/functional/PureFunctionsUnitTets.java

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+package com.baeldung.functional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Arrays;
+
+import org.junit.Test;
+
+public class PureFunctionsUnitTets {
+
+    @Test
+    public void testSortingWithoutLambda() {
+
+        assertEquals(new Integer(18), PureFunctions.sum(Arrays.asList(new Integer(10), new Integer(8))));
+
+    }
+
+}

core-java-modules/core-java-functional/src/test/java/com/baeldung/functional/RecursionUnitTest.java

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+package com.baeldung.functional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.Test;
+
+public class RecursionUnitTest {
+
+    @Test
+    public void testHeadRecursion() {
+
+        assertEquals(120, Recursion.headRecursion(5));
+
+    }
+
+    @Test
+    public void testTailRecursion() {
+
+        assertEquals(120, Recursion.tailRecursion(5, 1));
+
+    }
+
+}

core-java-modules/pom.xml

@@ -60,6 +60,7 @@
         <module>core-java-exceptions-2</module>
         <module>core-java-exceptions-3</module>
         <module>core-java-function</module>
+		<module>core-java-functional</module>
 
         <module>core-java-io</module>
         <module>core-java-io-2</module>