8000 Stream.,map() helpers · allwaysoft/Java-Coding-Problems@671c6ff · GitHub
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Stream.,map() helpers
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‎Chapter09/P182_MapStreamHelpers/README.md

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# Map a stream
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Write several examples of mapping a stream via **map()** and **flatMap()**.

‎Chapter09/P182_MapStreamHelpers/pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<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">
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<modelVersion>4.0.0</modelVersion>
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<groupId>coding.challenge</groupId>
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<artifactId>P182_MapStreamHelpers</artifactId>
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<version>1.0</version>
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<packaging>jar</packaging>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<maven.compiler.source>13</maven.compiler.source>
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<maven.compiler.target>13</maven.compiler.target>
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</properties>
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<name>P182_MapStreamHelpers</name>
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</project>

‎Chapter09/P182_MapStreamHelpers/src/main/java/modern/challenge/Convertors.java

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package modern.challenge;
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import java.util.Arrays;
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import java.util.List;
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import java.util.function.Function;
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import java.util.function.IntFunction;
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import java.util.stream.Collectors;
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public final class Convertors {
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private Convertors() {
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throw new AssertionError("Cannot be instantiated");
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}
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// converter for lists
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public static <P, Q> List<Q> list(List<P> source, Function<P, Q> f) {
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if(source == null || f == null) {
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throw new IllegalArgumentException("Inputs cannot be null");
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}
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return source.stream()
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.map(f)
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.collect(Collectors.toList());
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}
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// converter for arrays
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public static <P, Q> Q[] array(P[] source, Function<P, Q> f, IntFunction<Q[]> generator) {
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if(source == null || f == null || generator == null) {
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throw new IllegalArgumentException("Inputs cannot be null");
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}
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return Arrays.stream(source)
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.map(f)
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.toArray(generator);
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}
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}

‎Chapter09/P182_MapStreamHelpers/src/main/java/modern/challenge/Main.java

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package modern.challenge;
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import java.util.Arrays;
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import java.util.List;
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public class Main {
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public static void main(String[] args) {
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System.out.println("Convert list of String to list of ints:");
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List<String> strList = Arrays.asList("11", "22", "33");
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List<Integer> intList = Convertors.list(strList, Integer::parseInt);
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System.out.println("strList: " + strList);
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System.out.println("intList: " + intList);
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System.out.println("\n\nConvert array of String to array of doubles:");
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String[] strArr = {"11", "22", "34"};
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Double[] doubleArr = Convertors.array(strArr, Double::parseDouble, Double[]::new);
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System.out.println("strArr: " + Arrays.toString(strArr));
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System.out.println("doubleArr: " + Arrays.toString(doubleArr));
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}
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}

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