[BAEL-2835] Added Guide to FastUtil code (#6805)

fastUtil/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>
+
+    <groupId>com.baeldung</groupId>
+    <artifactId>fastUtil</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <dependencies>
+<!-- https://mvnrepository.com/artifact/it.unimi.dsi/fastutil -->
+<dependency>
+    <groupId>it.unimi.dsi</groupId>
+    <artifactId>fastutil</artifactId>
+    <version>8.2.2</version>
+</dependency>
+<!-- https://mvnrepository.com/artifact/junit/junit -->
+<dependency>
+    <groupId>junit</groupId>
+    <artifactId>junit</artifactId>
+    <version>4.12</version>
+    <scope>test</scope>
+</dependency>
+<!-- https://mvnrepository.com/artifact/org.openjdk.jmh/jmh-core -->
+<dependency>
+    <groupId>org.openjdk.jmh</groupId>
+    <artifactId>jmh-core</artifactId>
+    <version>1.19</version>
+    <scope>test</scope>
+</dependency>
+<dependency>
+    <groupId>org.openjdk.jmh</groupId>
+    <artifactId>jmh-generator-annprocess</artifactId>
+    <version>1.19</version>
+    <scope>test</scope>
+</dependency>
+
+
+
+    </dependencies>
+
+
+</project>

fastUtil/src/test/java/com/baeldung/BigArraysUnitTest.java

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+package com.baeldung;
+
+import it.unimi.dsi.fastutil.ints.IntBigArrays;
+import org.junit.Test;
+
+import static junit.framework.Assert.assertEquals;
+
+public class BigArraysUnitTest {
+
+  @Test
+  public void givenValidAray_whenWrapped_checkAccessFromIntBigArraysMethodsCorrect() {
+    int[] oneDArray = new int[] { 2, 1, 5, 2, 1, 7 };
+    int[][] twoDArray = IntBigArrays.wrap(oneDArray.clone());
+
+    int firstIndex = IntBigArrays.get(twoDArray, 0);
+    int lastIndex = IntBigArrays.get(twoDArray, IntBigArrays.length(twoDArray)-1);
+
+    assertEquals(2, firstIndex);
+    assertEquals(7, lastIndex);
+
+  }
+
+}

fastUtil/src/test/java/com/baeldung/FastUtilTypeSpecificBenchmarkUnitTest.java

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+package com.baeldung;
+
+import it.unimi.dsi.fastutil.ints.IntOpenHashSet;
+import it.unimi.dsi.fastutil.ints.IntSet;
+import org.openjdk.jmh.annotations.*;
+import org.openjdk.jmh.infra.Blackhole;
+import org.openjdk.jmh.runner.Runner;
+import org.openjdk.jmh.runner.RunnerException;
+import org.openjdk.jmh.runner.options.Options;
+import org.openjdk.jmh.runner.options.OptionsBuilder;
+
+import java.util.*;
+import java.util.concurrent.TimeUnit;
+
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.MICROSECONDS)
+@State(Scope.Benchmark)
+public class FastUtilTypeSpecificBenchmarkUnitTest {
+
+  @Param({"100", "1000", "10000", "100000"})
+  public int setSize;
+
+  @Benchmark
+  public IntSet givenFastUtilsIntSetWithInitialSizeSet_whenPopulated_checkTimeTaken() {
+    IntSet intSet = new IntOpenHashSet(setSize);
+    for(int i = 0; i < setSize; i++){
+      intSet.add(i);
+    }
+    return intSet;
+  }
+
+
+  @Benchmark
+  public Set<Integer> givenCollectionsHashSetWithInitialSizeSet_whenPopulated_checkTimeTaken() {
+    Set<Integer> intSet = new HashSet<Integer>(setSize);
+    for(int i = 0; i < setSize; i++){
+      intSet.add(i);
+    }
+    return intSet;
+  }
+
+  public static void main(String... args) throws RunnerException {
+    Options opts = new OptionsBuilder()
+            .include(".*")
+            .warmupIterations(1)
+            .measurementIterations(2)
+            .jvmArgs("-Xms2g", "-Xmx2g")
+            .shouldDoGC(true)
+            .forks(1)
+            .build();
+
+    new Runner(opts).run();
+  }
+
+
+
+
+}

fastUtil/src/test/java/com/baeldung/FastUtilTypeSpecificUnitTest.java

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+package com.baeldung;
+
+import it.unimi.dsi.fastutil.doubles.Double2DoubleMap;
+import it.unimi.dsi.fastutil.doubles.Double2DoubleOpenHashMap;
+import org.junit.Test;
+
+import static junit.framework.Assert.assertEquals;
+
+
+public class FastUtilTypeSpecificUnitTest {
+
+  @Test
+  public void givenValidDouble2DoubleMap_whenContentsQueried_checkCorrect(){
+    Double2DoubleMap d2dMap = new Double2DoubleOpenHashMap();
+    d2dMap.put(2.0, 5.5);
+    d2dMap.put(3.0, 6.6);
+    assertEquals(5.5, d2dMap.get(2.0));
+  }
+
+}