Functional Style Programming - a Deep Dive

AnghelLeonard · AnghelLeonard · commit a4e3fe1a6ef4 · 2020-05-31T12:59:39.000+03:00
diff --git a/Chapter09/BONUS_1_ArrayToStreamAndBack/README.md b/Chapter09/BONUS_1_ArrayToStreamAndBack/README.md
@@ -0,0 +1,2 @@
+# Map a stream
+Write a helper method that uses **Stream#map()** to convert **List< P >** in **List< Q >**. Write a heper method that does the same thing for arrays.
diff --git a/Chapter09/BONUS_1_ArrayToStreamAndBack/pom.xml b/Chapter09/BONUS_1_ArrayToStreamAndBack/pom.xml
@@ -0,0 +1,14 @@
+<?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>
+    <groupId>coding.challenge</groupId>
+    <artifactId>BONUS_1_ArrayToStreamAndBack</artifactId>
+    <version>1.0</version>
+    <packaging>jar</packaging>
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>13</maven.compiler.source>
+        <maven.compiler.target>13</maven.compiler.target>
+    </properties>
+    <name>BONUS_1_ArrayToStreamAndBack</name>
+</project>
diff --git a/Chapter09/BONUS_1_ArrayToStreamAndBack/src/main/java/modern/challenge/Convertors.java b/Chapter09/BONUS_1_ArrayToStreamAndBack/src/main/java/modern/challenge/Convertors.java
@@ -0,0 +1,62 @@
+package modern.challenge;
+
+import java.util.Arrays;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+public final class Convertors {
+
+    private Convertors() {
+        throw new AssertionError("Cannot be instantiated");
+    }
+
+    // Convert array of T to stream via Arrays#stream()
+    public static <T> Stream<T> toStream1(T[] arr) {
+
+        if (arr == null) {
+            throw new IllegalArgumentException("Inputs cannot be null");
+        }
+
+        return Arrays.stream(arr);
+    }
+
+    // Convert array of T to stream via Stream#of()
+    public static <T> Stream<T> toStream2(T[] arr) {
+
+        if (arr == null) {
+            throw new IllegalArgumentException("Inputs cannot be null");
+        }
+
+        return Stream.of(arr);
+    }
+
+    // Convert array of T to stream via List#stream()
+    public static <T> Stream<T> toStream3(T[] arr) {
+
+        if (arr == null) {
+            throw new IllegalArgumentException("Inputs cannot be null");
+        }
+
+        return Arrays.asList(arr).stream();
+    }
+
+    // Convert array of primitves (int) to stream via Arrays#stream()
+    public static IntStream toStream4(int[] arr) {
+
+        if (arr == null) {
+            throw new IllegalArgumentException("Inputs cannot be null");
+        }
+
+        return Arrays.stream(arr);
+    }
+
+    // Convert array of primitves (int) to stream via IntStream#of()
+    public static IntStream toStream5(int[] arr) {
+
+        if (arr == null) {
+            throw new IllegalArgumentException("Inputs cannot be null");
+        }
+
+        return IntStream.of(arr);
+    }        
+}
diff --git a/Chapter09/BONUS_1_ArrayToStreamAndBack/src/main/java/modern/challenge/Main.java b/Chapter09/BONUS_1_ArrayToStreamAndBack/src/main/java/modern/challenge/Main.java
@@ -0,0 +1,35 @@
+package modern.challenge;
+
+public class Main {
+
+    public static void main(String[] args) {
+
+        Melon[] melons = {
+            new Melon("Gac", 1200),
+            new Melon("Hemi", 2300),
+            new Melon("Apollo", 3400)
+        };
+
+        int[] weights = {1200, 2300, 3400};
+
+        System.out.println("Array of melons to stream (toStream1()):");
+        Convertors.toStream1(melons)
+                .forEach(System.out::println);
+
+        System.out.println("\n\nArray of melons to stream (toStream2()):");
+        Convertors.toStream2(melons)
+                .forEach(System.out::println);
+
+        System.out.println("\n\nArray of melons to stream (toStream3()):");
+        Convertors.toStream3(melons)
+                .forEach(System.out::println);
+
+        System.out.println("\n\nArray of integers to stream (toStream4()):");
+        Convertors.toStream4(weights)
+                .forEach(System.out::println);
+
+        System.out.println("\n\nArray of integers to stream (toStream5()):");
+        Convertors.toStream5(weights)
+                .forEach(System.out::println);
+    }
+}
diff --git a/Chapter09/BONUS_1_ArrayToStreamAndBack/src/main/java/modern/challenge/Melon.java b/Chapter09/BONUS_1_ArrayToStreamAndBack/src/main/java/modern/challenge/Melon.java
@@ -0,0 +1,70 @@
+package modern.challenge;
+
+import java.util.Objects;
+
+public class Melon {
+
+    private String type;
+    private int weight;
+
+    public Melon(String type, int weight) {
+        this.type = type;
+        this.weight = weight;
+    }
+
+    public String getType() {
+        return type;
+    }
+
+    public int getWeight() {
+        return weight;
+    }
+
+    public void setType(String type) {
+        this.type = type;
+    }
+
+    public void setWeight(int weight) {
+        this.weight = weight;
+    }
+
+    @Override
+    public String toString() {
+        return type + "(" + weight + "g)";
+    }
+
+    @Override
+    public int hashCode() {
+        int hash = 7;
+        hash = 37 * hash + Objects.hashCode(this.type);
+        hash = 37 * hash + this.weight;
+        return hash;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        
+        if (this == obj) {
+            return true;
+        }
+        
+        if (obj == null) {
+            return false;
+        }
+        
+        if (getClass() != obj.getClass()) {
+            return false;
+        }
+        
+        final Melon other = (Melon) obj;
+        if (this.weight != other.weight) {
+            return false;
+        }
+        
+        if (!Objects.equals(this.type, other.type)) {
+            return false;
+        }
+        return true;
+    }
+
+}

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	`+# Map a stream`
	`2`	`+Write a helper method that uses Stream#map() to convert List< P > in List< Q >. Write a heper method that does the same thing for arrays.`