Merge remote-tracking branch 'upstream/master' into docker_compose_restart_policies

apache-poi-2/pom.xml

@@ -1,7 +1,7 @@
 <?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">
+    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>apache-poi-2</artifactId>
     <version>0.0.1-SNAPSHOT</version>
@@ -25,5 +25,4 @@
         <poi.version>5.2.0</poi.version>
     </properties>
 
-</project>
-
+</project>

apache-spark/README.md

@@ -9,3 +9,4 @@ This module contains articles about Apache Spark
 - [Machine Learning with Spark MLlib](https://www.baeldung.com/spark-mlib-machine-learning)
 - [Introduction to Spark Graph Processing with GraphFrames](https://www.baeldung.com/spark-graph-graphframes)
 - [Apache Spark: Differences between Dataframes, Datasets and RDDs](https://www.baeldung.com/java-spark-dataframe-dataset-rdd)
+- [Spark DataFrame](https://www.baeldung.com/spark-dataframes)

apache-spark/src/test/java/com/baeldung/differences/rdd/ActionsUnitTest.java

@@ -12,21 +12,29 @@ import org.junit.AfterClass;
 import org.junit.BeforeClass;
 import org.junit.Test;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import scala.Tuple2;
 
 public class ActionsUnitTest {
+
+    public static final Logger LOG = LoggerFactory.getLogger(ActionsUnitTest.class);
+
     private static JavaRDD<String> tourists;
     private static JavaSparkContext sc;
     public static final String COMMA_DELIMITER = ",(?=([^\"]*\"[^\"]*\")*[^\"]*$)";
-    
+
     @BeforeClass
     public static void init() {
-        SparkConf conf = new SparkConf().setAppName("reduce")
-            .setMaster("local[*]");
+        SparkConf conf = new SparkConf()
+          .setAppName("reduce")
+          .setMaster("local[*]")
+          .set("spark.driver.allowMultipleContexts", "true");
+
         sc = new JavaSparkContext(conf);
         tourists = sc.textFile("data/Tourist.csv").filter(line -> !line.startsWith("Region"));
     }
-    
+
     @AfterClass
     public static void cleanup() {
         sc.close();
@@ -40,11 +48,11 @@ public class ActionsUnitTest {
         })
             .distinct();
         Long numberOfCountries = countries.count();
-        System.out.println("Count: " + numberOfCountries);
-        
+        LOG.debug("Count: {}", numberOfCountries);
+
         assertEquals(Long.valueOf(220), numberOfCountries);
     }
-    
+
     @Test
     public void whenReduceByKeySum_thenTotalValuePerKey() {
         JavaRDD<String> touristsExpenditure = tourists.filter(line -> line.split(COMMA_DELIMITER)[3].contains("expenditure"));
@@ -53,10 +61,12 @@ public class ActionsUnitTest {
             String[] columns = line.split(COMMA_DELIMITER);
             return new Tuple2<>(columns[1], Double.valueOf(columns[6]));
         });
-        List<Tuple2<String, Double>> totalByCountry = expenditurePairRdd.reduceByKey((x, y) -> x + y)
-            .collect();
-        System.out.println("Total per Country: " + totalByCountry);
-        
+        List<Tuple2<String, Double>> totalByCountry = expenditurePairRdd
+          .reduceByKey(Double::sum)
+          .collect();
+
+        LOG.debug("Total per Country: {}", totalByCountry);
+
         for(Tuple2<String, Double> tuple : totalByCountry) {
             if (tuple._1.equals("Mexico")) {
                 assertEquals(Double.valueOf(99164), tuple._2);

apache-spark/src/test/java/com/baeldung/differences/rdd/DataFrameUnitTest.java

@@ -39,8 +39,10 @@ public class DataFrameUnitTest {
     @Test
     public void whenSelectSpecificColumns_thenColumnsFiltered() {
         Dataset<Row> selectedData = data.select(col("country"), col("year"), col("value"));
-        selectedData.show();
-        
+
+        // uncomment to see table
+        // selectedData.show();
+
         List<String> resultList = Arrays.asList(selectedData.columns());
         assertTrue(resultList.contains("country"));
         assertTrue(resultList.contains("year"));
@@ -52,22 +54,26 @@ public class DataFrameUnitTest {
     @Test
     public void whenFilteringByCountry_thenCountryRecordsSelected() {
         Dataset<Row> filteredData = data.filter(col("country").equalTo("Mexico"));
-        filteredData.show();
-        
+
+        // uncomment to see table
+        // filteredData.show();
+
         filteredData.foreach(record -> {
             assertEquals("Mexico", record.get(1));
         });
-        
+
     }
 
     @Test
     public void whenGroupCountByCountry_thenContryTotalRecords() {
         Dataset<Row> recordsPerCountry = data.groupBy(col("country"))
             .count();
-        recordsPerCountry.show();
-        
+
+        // uncomment to see table
+        // recordsPerCountry.show();
+
         Dataset<Row> filteredData = recordsPerCountry.filter(col("country").equalTo("Sweden"));
-        assertEquals(new Long(12), filteredData.first()
+        assertEquals(12L, filteredData.first()
             .get(1));
     }
 

apache-spark/src/test/java/com/baeldung/differences/rdd/DatasetUnitTest.java

@@ -3,6 +3,7 @@ package com.baeldung.differences.rdd;
 import static org.apache.spark.sql.functions.col;
 import static org.apache.spark.sql.functions.sum;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 
 import org.apache.spark.api.java.function.FilterFunction;
 import org.apache.spark.sql.DataFrameReader;
@@ -29,8 +30,8 @@ public class DatasetUnitTest {
         DataFrameReader dataFrameReader = session.read();
         Dataset<Row> data = dataFrameReader.option("header", "true")
             .csv("data/Tourist.csv");
-        Dataset<Row> responseWithSelectedColumns = data.select(col("region"), 
-            col("country"), col("year"), col("series"), col("value").cast("double"), 
+        Dataset<Row> responseWithSelectedColumns = data.select(col("region"),
+            col("country"), col("year"), col("series"), col("value").cast("double"),
             col("footnotes"), col("source"));
         typedDataset = responseWithSelectedColumns.as(Encoders.bean(TouristData.class));
     }
@@ -45,7 +46,9 @@ public class DatasetUnitTest {
         Dataset<TouristData> selectedData = typedDataset
             .filter((FilterFunction<TouristData>) record -> record.getCountry()
             .equals("Norway"));
-        selectedData.show();
+
+        // uncomment to see output
+        // selectedData.show();
 
         selectedData.foreach(record -> {
             assertEquals("Norway", record.getCountry());
@@ -56,28 +59,41 @@ public class DatasetUnitTest {
     public void whenGroupCountByCountry_thenContryTotalRecords() {
         Dataset<Row> countriesCount = typedDataset.groupBy(typedDataset.col("country"))
             .count();
-        countriesCount.show();
 
-        assertEquals(Long.valueOf(220), Long.valueOf(countriesCount.count()));
+        // uncomment to see output
+        // countriesCount.show();
+
+        assertEquals(220, countriesCount.count());
     }
 
     @Test
     public void whenFilteredByPropertyRange_thenRetreiveValidRecords() {
         // Filter records with existing data for years between 2010 and 2017
-        typedDataset.filter((FilterFunction<TouristData>) record -> record.getYear() != null 
-            && (Long.valueOf(record.getYear()) > 2010 && Long.valueOf(record.getYear()) < 2017))
-            .show();
+        Dataset<TouristData> filteredData = typedDataset.filter(
+          (FilterFunction<TouristData>) record -> record.getYear() != null
+            && (Long.parseLong(record.getYear()) > 2010 && Long.parseLong(record.getYear()) < 2017));
+
+        // uncomment to see output
+        // filteredData.show();
+
+        assertEquals(394, filteredData.count());
+        filteredData.foreach(record -> {
+            assertTrue(Integer.parseInt(record.getYear()) > 2010 && Integer.parseInt(record.getYear()) < 2017);
+        });
     }
-    
+
     @Test
     public void whenSumValue_thenRetreiveTotalValue() {
         // Total tourist expenditure by country
-        typedDataset.filter((FilterFunction<TouristData>) record -> record.getValue() != null 
-            && record.getSeries()
-            .contains("expenditure"))
-            .groupBy("country")
-            .agg(sum("value"))
-            .show();
+        Dataset<Row> filteredData = typedDataset.filter((FilterFunction<TouristData>) record -> record.getValue() != null
+            && record.getSeries().contains("expenditure"))
+          .groupBy("country")
+          .agg(sum("value"));
+
+        // uncomment to see output
+        // filteredData.show();
+
+        assertEquals(212, filteredData.count());
     }
 
 }

apache-spark/src/test/java/com/baeldung/differences/rdd/TransformationsUnitTest.java

@@ -23,8 +23,11 @@ public class TransformationsUnitTest {
 
     @BeforeClass
     public static void init() {
-        SparkConf conf = new SparkConf().setAppName("uppercaseCountries")
-            .setMaster("local[*]");
+        SparkConf conf = new SparkConf()
+          .setAppName("uppercaseCountries")
+          .setMaster("local[*]")
+          .set("spark.driver.allowMultipleContexts", "true");
+
         sc = new JavaSparkContext(conf);
         tourists = sc.textFile("data/Tourist.csv")
             .filter(line -> !line.startsWith("Region")); //filter header row

apache-tapestry/pom.xml

@@ -3,12 +3,17 @@
     xmlns="http://maven.apache.org/POM/4.0.0"
     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
     <modelVersion>4.0.0</modelVersion>
-    <groupId>com.baeldung</groupId>
     <artifactId>apache-tapestry</artifactId>
     <version>0.0.1-SNAPSHOT</version>
     <name>apache-tapestry</name>
     <packaging>war</packaging>
 
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
     <dependencies>
         <!-- To set up an application with a database, change the artifactId below to tapestry-hibernate, 
             and add a dependency on your JDBC driver. You'll also need to add Hibernate configuration files, such 

aws-modules/aws-lambda/shipping-tracker/ShippingFunction/pom.xml

@@ -8,6 +8,13 @@
     <name>ShippingFunction</name>
     <packaging>jar</packaging>
 
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>aws-lambda</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+        <relativePath>../../</relativePath>
+    </parent>
+
     <dependencies>
         <dependency>
             <groupId>com.amazonaws</groupId>

aws-modules/aws-miscellaneous/pom.xml

@@ -78,6 +78,25 @@
                     </execution>
                 </executions>
             </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-dependency-plugin</artifactId>
+                <version>${maven-plugins-version}</version>
+                <executions>
+                    <execution>
+                        <id>copy</id>
+                        <phase>compile</phase>
+                        <goals>
+                            <goal>copy-dependencies</goal>
+                        </goals>
+                        <configuration>
+                            <includeScope></includeScope>
+                            <includeTypes>so,dll,dylib</includeTypes>
+                            <outputDirectory>native-libs</outputDirectory>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
         </plugins>
     </build>
 
@@ -99,6 +118,7 @@
         <commons-codec-version>1.10.L001</commons-codec-version>
         <jets3t-version>0.9.4.0006L</jets3t-version>
         <maven-shade-plugin.version>3.0.0</maven-shade-plugin.version>
+        <maven-plugins-version>3.1.1</maven-plugins-version>
     </properties>
 
 </project>

aws-modules/aws-s3/pom.xml

@@ -20,7 +20,6 @@
             <artifactId>aws-java-sdk</artifactId>
             <version>${aws-java-sdk.version}</version>
         </dependency>
-        
         <dependency>
             <groupId>commons-io</groupId>
             <artifactId>commons-io</artifactId>
@@ -58,7 +57,7 @@
                 </executions>
             </plugin>
         </plugins>
-    </build>    
+    </build>
 
     <properties>
         <aws-java-sdk.version>1.11.290</aws-java-sdk.version>

aws-modules/pom.xml

@@ -19,6 +19,6 @@
         <module>aws-miscellaneous</module>
         <module>aws-reactive</module>
         <module>aws-s3</module>
-    </modules>    
+    </modules>
 
 </project>

core-java-modules/core-java-11-2/README.md

@@ -12,3 +12,4 @@ This module contains articles about Java 11 core features
 - [Java HTTPS Client Certificate Authentication](https://www.baeldung.com/java-https-client-certificate-authentication)
 - [Call Methods at Runtime Using Java Reflection](https://www.baeldung.com/java-method-reflection)
 - [Java HttpClient Basic Authentication](https://www.baeldung.com/java-httpclient-basic-auth)
+- [Java HttpClient With SSL](https://www.baeldung.com/java-httpclient-ssl)

core-java-modules/core-java-11-2/src/test/java/com/baeldung/httpclient/ssl/HttpClientSSLBypassUnitTest.java

@@ -0,0 +1,32 @@
+package com.baeldung.httpclient.ssl;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.util.Properties;
+
+public class HttpClientSSLBypassUnitTest {
+
+    @Test
+    public void whenHttpsRequest_thenCorrect() throws IOException, InterruptedException {
+        final Properties props = System.getProperties();
+        props.setProperty("jdk.internal.httpclient.disableHostnameVerification", Boolean.TRUE.toString());
+
+        HttpClient httpClient = HttpClient.newBuilder()
+          .build();
+
+        HttpRequest request = HttpRequest.newBuilder()
+          .uri(URI.create("https://www.testingmcafeesites.com/"))
+          .build();
+
+        HttpResponse<String> response = httpClient.send(request, HttpResponse.BodyHandlers.ofString());
+        props.setProperty("jdk.internal.httpclient.disableHostnameVerification", Boolean.FALSE.toString());
+
+        Assertions.assertEquals(200, response.statusCode());
+    }
+}

core-java-modules/core-java-11-2/src/test/java/com/baeldung/httpclient/ssl/HttpClientSSLUnitTest.java

@@ -0,0 +1,41 @@
+package com.baeldung.httpclient.ssl;
+
+import org.junit.Test;
+
+import javax.net.ssl.SSLHandshakeException;
+import java.io.IOException;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+
+import static org.junit.Assert.assertEquals;
+
+public class HttpClientSSLUnitTest {
+
+    @Test
+    public void whenValidHttpsRequest_thenCorrect() throws URISyntaxException, IOException, InterruptedException {
+        HttpClient httpClient = HttpClient.newHttpClient();
+        HttpRequest request = HttpRequest.newBuilder()
+          .uri(new URI("https://www.google.com/"))
+          .build();
+
+        HttpResponse<String> response = httpClient.send(request, HttpResponse.BodyHandlers.ofString());
+
+        assertEquals(200, response.statusCode());
+    }
+
+    @Test(expected = SSLHandshakeException.class)
+    public void whenInvalidHttpsRequest_thenInCorrect() throws IOException, InterruptedException {
+        HttpClient httpClient = HttpClient.newHttpClient();
+        HttpRequest request = HttpRequest.newBuilder()
+          .uri(URI.create("https://expired.badssl.com/"))
+          .build();
+
+        HttpResponse<String> response = httpClient.send(request, HttpResponse.BodyHandlers.ofString());
+
+        assertEquals(200, response.statusCode());
+    }
+
+}

core-java-modules/core-java-9/src/main/java/com/baeldung/java9/delimiters/DelimiterDemo.java

@@ -0,0 +1,36 @@
+package com.baeldung.java9.delimiters;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Scanner;
+import java.util.regex.Pattern;
+
+public class DelimiterDemo {
+
+    public static List<String> scannerWithDelimiter(String input, String delimiter) {
+        try (Scanner scan = new Scanner(input)) {
+            scan.useDelimiter(delimiter);
+            List<String> result = new ArrayList<String>();
+            scan.forEachRemaining(result::add);
+            return result;
+        }
+    }
+
+    public static List<String> scannerWithDelimiterUsingPattern(String input, Pattern delimiter) {
+        try (Scanner scan = new Scanner(input)) {
+            scan.useDelimiter(delimiter);
+            List<String> result = new ArrayList<String>();
+            scan.forEachRemaining(result::add);
+            return result;
+        }
+    }
+
+    public static List<String> baseScanner(String input) {
+        try (Scanner scan = new Scanner(input)) {
+            List<String> result = new ArrayList<String>();
+            scan.forEachRemaining(result::add);
+            return result;
+        }
+    }
+
+}

core-java-modules/core-java-9/src/test/java/com/baeldung/java9/delimiters/DelimiterDemoUnitTest.java

@@ -0,0 +1,67 @@
+package com.baeldung.java9.delimiters;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.BiFunction;
+import java.util.regex.Pattern;
+
+import org.junit.jupiter.api.Test;
+
+class DelimiterDemoUnitTest {
+
+    @Test
+    void givenSimpleCharacterDelimiter_whenScannerWithDelimiter_ThenInputIsCorrectlyParsed() {
+        checkOutput(DelimiterDemo::scannerWithDelimiter, "Welcome to Baeldung", "\\s", Arrays.asList("Welcome", "to", "Baeldung"));
+    }
+
+    @Test
+    void givenStringDelimiter_whenScannerWithDelimiter_ThenInputIsCorrectlyParsed() {
+        checkOutput(DelimiterDemo::scannerWithDelimiter, "HelloBaeldungHelloWorld", "Hello", Arrays.asList("Baeldung", "World"));
+    }
+
+    @Test
+    void givenVariousPossibleDelimiters_whenScannerWithDelimiter_ThenInputIsCorrectlyParsed() {
+        checkOutput(DelimiterDemo::scannerWithDelimiter, "Welcome to Baeldung.\nThank you for reading.\nThe team", "\n|\\s", Arrays.asList("Welcome", "to", "Baeldung.", "Thank", "you", "for", "reading.", "The", "team"));
+    }
+
+    @Test
+    void givenWildcardRegexDelimiter_whenScannerWithDelimiter_ThenInputIsCorrectlyParsed() {
+        checkOutput(DelimiterDemo::scannerWithDelimiter, "1aaaaaaa2aa3aaa4", "a+", Arrays.asList("1", "2", "3", "4"));
+    }
+
+    @Test
+    void givenSimpleCharacterDelimiter_whenScannerWithDelimiterUsingPattern_ThenInputIsCorrectlyParsed() {
+        checkOutput(DelimiterDemo::scannerWithDelimiterUsingPattern, "Welcome to Baeldung", Pattern.compile("\\s"), Arrays.asList("Welcome", "to", "Baeldung"));
+    }
+
+    @Test
+    void givenStringDelimiter_whenScannerWithDelimiterUsingPattern_ThenInputIsCorrectlyParsed() {
+        checkOutput(DelimiterDemo::scannerWithDelimiterUsingPattern, "HelloBaeldungHelloWorld", Pattern.compile("Hello"), Arrays.asList("Baeldung", "World"));
+    }
+
+    @Test
+    void givenVariousPossibleDelimiters_whenScannerWithDelimiterUsingPattern_ThenInputIsCorrectlyParsed() {
+        checkOutput(DelimiterDemo::scannerWithDelimiterUsingPattern, "Welcome to Baeldung.\nThank you for reading.\nThe team", Pattern.compile("\n|\\s"), Arrays.asList("Welcome", "to", "Baeldung.", "Thank", "you", "for", "reading.", "The", "team"));
+    }
+
+    @Test
+    void givenWildcardRegexDelimiters_whenScannerWithDelimiterUsingPattern_ThenInputIsCorrectlyParsed() {
+        checkOutput(DelimiterDemo::scannerWithDelimiterUsingPattern, "1aaaaaaa2aa3aaa4", Pattern.compile("a*"), Arrays.asList("1", "2", "3", "4"));
+    }
+
+    void checkOutput(BiFunction<String, String, List<String>> function, String input, String delimiter, List<String> expectedOutput) {
+        assertEquals(expectedOutput, function.apply(input, delimiter));
+    }
+
+    void checkOutput(BiFunction<String, Pattern, List<String>> function, String input, Pattern delimiter, List<String> expectedOutput) {
+        assertEquals(expectedOutput, function.apply(input, delimiter));
+    }
+
+    @Test
+    void whenBaseScanner_ThenWhitespacesAreUsedAsDelimiters() {
+        assertEquals(List.of("Welcome", "at", "Baeldung"), DelimiterDemo.baseScanner("Welcome at Baeldung"));
+    }
+
+}

core-java-modules/core-java-collections-2/README.md

@@ -12,3 +12,4 @@
 - [Sorting in Java](https://www.baeldung.com/java-sorting)
 - [Getting the Size of an Iterable in Java](https://www.baeldung.com/java-iterable-size)
 - [Java Null-Safe Streams from Collections](https://www.baeldung.com/java-null-safe-streams-from-collections)
+- [Differences Between Iterator and Iterable and How to Use Them?](https://www.baeldung.com/java-iterator-vs-iterable)

core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/CustomIterableClient.java

@@ -0,0 +1,17 @@
+package com.baeldung.collections.iterable;
+
+class CustomIterableClient {
+
+    public static void main(String[] args) {
+
+        ShoppingCart<Product> shoppingCart = new ShoppingCart<>();
+        shoppingCart.add(new Product("Tuna", 42));
+        shoppingCart.add(new Product("Eggplant", 65));
+        shoppingCart.add(new Product("Salad", 45));
+        shoppingCart.add(new Product("Banana", 29));
+
+        for (Product product : shoppingCart) {
+            System.out.println(product.getName());
+        }
+    }
+}

core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/IterableExample.java

@@ -0,0 +1,32 @@
+package com.baeldung.collections.iterable;
+
+import java.util.Iterator;
+import java.util.List;
+
+public class IterableExample {
+
+    public void iterateUsingIterator(List<Integer> numbers) {
+        Iterator<Integer> iterator = numbers.iterator();
+        while (iterator.hasNext()) {
+            System.out.println(iterator.next());
+        }
+    }
+
+    public void iterateUsingEnhancedForLoop(List<Integer> numbers) {
+        for (Integer number : numbers) {
+            System.out.println(number);
+        }
+    }
+
+    public void iterateUsingForEachLoop(List<Integer> numbers) {
+        numbers.forEach(System.out::println);
+    }
+
+    public void removeElementsUsingIterator(List<Integer> numbers) {
+        Iterator<Integer> iterator = numbers.iterator();
+        while (iterator.hasNext()) {
+            iterator.next();
+            iterator.remove();
+        }
+    }
+}

core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/Product.java

@@ -0,0 +1,28 @@
+package com.baeldung.collections.iterable;
+
+class Product {
+
+    private String name;
+    private double price;
+
+    public Product(String code, double price) {
+        this.name = code;
+        this.price = price;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public double getPrice() {
+        return price;
+    }
+
+    public void setPrice(double price) {
+        this.price = price;
+    }
+}

core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/ShoppingCart.java

@@ -0,0 +1,72 @@
+package com.baeldung.collections.iterable;
+
+import java.util.Arrays;
+import java.util.ConcurrentModificationException;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+public class ShoppingCart<E> implements Iterable<E> {
+
+    private E[] elementData;
+    private int size;
+
+    public ShoppingCart() {
+        this.elementData = (E[]) new Object[]{};
+    }
+
+    public void add(E element) {
+        ensureCapacity(size + 1);
+        elementData[size++] = element;
+    }
+
+    private void ensureCapacity(int minCapacity) {
+        int oldCapacity = elementData.length;
+        int newCapacity = oldCapacity + (oldCapacity >> 1);
+        if (newCapacity - minCapacity < 0) {
+            newCapacity = minCapacity;
+        }
+        elementData = Arrays.copyOf(elementData, newCapacity);
+    }
+
+    @Override
+    public Iterator<E> iterator() {
+        return new ShoppingCartIterator();
+    }
+
+    public class ShoppingCartIterator implements Iterator<E> {
+        int cursor;
+        int lastReturned = -1;
+
+        public boolean hasNext() {
+            return cursor != size;
+        }
+
+        public E next() {
+            return getNextElement();
+        }
+
+        private E getNextElement() {
+            int current = cursor;
+            exist(current);
+
+            E[] elements = ShoppingCart.this.elementData;
+            validate(elements, current);
+
+            cursor = current + 1;
+            lastReturned = current;
+            return elements[lastReturned];
+        }
+
+        private void exist(int current) {
+            if (current >= size) {
+                throw new NoSuchElementException();
+            }
+        }
+
+        private void validate(E[] elements, int current) {
+            if (current >= elements.length) {
+                throw new ConcurrentModificationException();
+            }
+        }
+    }
+}

core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterator/CustomIteratorClient.java

@@ -0,0 +1,14 @@
+package com.baeldung.collections.iterator;
+
+import java.util.Iterator;
+
+class CustomIteratorClient {
+
+    public static void main(String[] args) {
+        Iterator<Integer> iterator = Numbers.iterator();
+
+        while (iterator.hasNext()) {
+            System.out.println(iterator.next());
+        }
+    }
+}

core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterator/Numbers.java

@@ -0,0 +1,60 @@
+package com.baeldung.collections.iterator;
+
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.NoSuchElementException;
+
+class Numbers {
+
+    private static final List<Integer> NUMBER_LIST = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+
+    private Numbers() {
+    }
+
+    public static Iterator<Integer> iterator() {
+        return new PrimeIterator();
+    }
+
+    private static class PrimeIterator implements Iterator<Integer> {
+
+        private int cursor;
+
+        @Override
+        public Integer next() {
+            exist(cursor);
+            return NUMBER_LIST.get(cursor++);
+        }
+
+        private void exist(int current) {
+            if (current >= NUMBER_LIST.size()) {
+                throw new NoSuchElementException();
+            }
+        }
+
+        @Override
+        public boolean hasNext() {
+            if (cursor > NUMBER_LIST.size()) {
+                return false;
+            }
+
+            for (int i = cursor; i < NUMBER_LIST.size(); i++) {
+                if (isPrime(NUMBER_LIST.get(i))) {
+                    cursor = i;
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        private boolean isPrime(int number) {
+            for (int i = 2; i <= number / 2; ++i) {
+                if (number % i == 0) {
+                    return false;
+                }
+            }
+            return true;
+        }
+    }
+}

core-java-modules/core-java-collections-2/src/test/java/com/baeldung/collections/iterable/IterableUnitTest.java

@@ -0,0 +1,54 @@
+package com.baeldung.collections.iterable;
+
+import com.baeldung.collections.iterable.IterableExample;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class IterableUnitTest {
+
+    private static List<Integer> getNumbers() {
+        List<Integer> numbers = new ArrayList<>();
+        numbers.add(10);
+        numbers.add(20);
+        numbers.add(30);
+        numbers.add(40);
+        return numbers;
+    }
+
+    @Test
+    void givenNumbers_whenUsingIterator_thenCorrectSize() {
+        List<Integer> numbers = getNumbers();
+        IterableExample iterableExample = new IterableExample();
+        iterableExample.iterateUsingIterator(numbers);
+        assertEquals(4, numbers.size());
+    }
+
+    @Test
+    void givenNumbers_whenRemoveElements_thenEmptyList() {
+        List<Integer> numbers = getNumbers();
+        IterableExample iterableExample = new IterableExample();
+        iterableExample.removeElementsUsingIterator(numbers);
+        assertEquals(0, numbers.size());
+    }
+
+    @Test
+    void givenNumbers_whenIterateUsingEnhancedForLoop_thenCorrectSize() {
+        List<Integer> numbers = getNumbers();
+        IterableExample iterableExample = new IterableExample();
+        iterableExample.iterateUsingEnhancedForLoop(numbers);
+        assertEquals(4, numbers.size());
+    }
+
+    @Test
+    void givenNumbers_whenIterateUsingForEachLoop_thenCorrectSize() {
+        List<Integer> numbers = getNumbers();
+        IterableExample iterableExample = new IterableExample();
+        iterableExample.iterateUsingForEachLoop(numbers);
+        assertEquals(4, numbers.size());
+    }
+}

core-java-modules/core-java-collections-4/pom.xml

@@ -14,4 +14,16 @@
         <version>0.0.1-SNAPSHOT</version>
     </parent>
 
+    <dependencies>
+        <dependency>
+            <groupId>commons-lang</groupId>
+            <artifactId>commons-lang</artifactId>
+            <version>${commons-lang.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <commons-lang.version>2.2</commons-lang.version>
+    </properties>
+
 </project>

core-java-modules/core-java-collections-4/src/main/java/com/baeldung/collections/sorting/Employee.java

@@ -0,0 +1,72 @@
+package com.baeldung.collections.sorting;
+
+import java.util.Date;
+
+public class Employee implements Comparable<Employee>{
+
+  private String name;
+  private int age;
+  private double salary;
+  private Date joiningDate;
+
+  public Employee(String name, int age, double salary, Date joiningDate) {
+    this.name = name;
+    this.age = age;
+    this.salary = salary;
+    this.joiningDate = joiningDate;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public void setName(String name) {
+    this.name = name;
+  }
+
+  public int getAge() {
+    return age;
+  }
+
+  public void setAge(int age) {
+    this.age = age;
+  }
+
+  public double getSalary() {
+    return salary;
+  }
+
+  public void setSalary(double salary) {
+    this.salary = salary;
+  }
+
+  public Date getJoiningDate() {
+    return joiningDate;
+  }
+
+  public void setJoiningDate(Date joiningDate) {
+    this.joiningDate = joiningDate;
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    return ((Employee) obj).getName()
+      .equals(getName());
+  }
+
+  @Override
+  public String toString() {
+    return new StringBuffer().append("(")
+      .append(getName()).append(",")
+      .append(getAge())
+      .append(",")
+      .append(getSalary()).append(",").append(getJoiningDate())
+      .append(")")
+      .toString();
+  }
+
+  @Override
+  public int compareTo(Employee employee) {
+    return getJoiningDate().compareTo(employee.getJoiningDate());
+  }
+}

core-java-modules/core-java-collections-4/src/test/java/com/baeldung/collections/sorting/EmployeeSortingByDateUnitTest.java

@@ -0,0 +1,146 @@
+package com.baeldung.collections.sorting;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.Date;
+import java.util.List;
+import org.apache.commons.lang.time.DateUtils;
+import org.junit.Before;
+import org.junit.Test;
+
+public class EmployeeSortingByDateUnitTest {
+
+  private List<Employee> employees = new ArrayList<>();
+  private List<Employee> employeesSortedByDateAsc = new ArrayList<>();
+  private List<Employee> employeesSortedByDateDesc = new ArrayList<>();
+
+  @Before
+  public void initVariables() {
+
+    Collections.addAll(employees,
+      new Employee("Earl", 43, 10000, DateUtils.addMonths(new Date(), -2)),
+      new Employee("Frank", 33, 7000, DateUtils.addDays(new Date(), -20)),
+      new Employee("Steve", 26, 6000, DateUtils.addDays(new Date(), -10)),
+      new Employee("Jessica", 23, 4000, DateUtils.addMonths(new Date(), -6)),
+      new Employee("Pearl", 33, 6000, DateUtils.addYears(new Date(), -1)),
+      new Employee("John", 23, 5000, new Date())
+    );
+
+    Collections.addAll(employeesSortedByDateDesc,
+      new Employee("John", 23, 5000, new Date()),
+      new Employee("Steve", 26, 6000, DateUtils.addDays(new Date(), -10)),
+      new Employee("Frank", 33, 7000, DateUtils.addDays(new Date(), -20)),
+      new Employee("Earl", 43, 10000, DateUtils.addMonths(new Date(), -2)),
+      new Employee("Jessica", 23, 4000, DateUtils.addMonths(new Date(), -6)),
+      new Employee("Pearl", 33, 6000, DateUtils.addYears(new Date(), -1))
+    );
+
+    Collections.addAll(employeesSortedByDateAsc,
+      new Employee("Pearl", 33, 6000, DateUtils.addYears(new Date(), -1)),
+      new Employee("Jessica", 23, 4000, DateUtils.addMonths(new Date(), -6)),
+      new Employee("Earl", 43, 10000, DateUtils.addMonths(new Date(), -2)),
+      new Employee("Frank", 33, 7000, DateUtils.addDays(new Date(), -20)),
+      new Employee("Steve", 26, 6000, DateUtils.addDays(new Date(), -10)),
+      new Employee("John", 23, 5000, new Date())
+    );
+  }
+
+  @Test
+  public void givenEmpList_SortEmpList_thenSortedListinNaturalOrder() {
+    Collections.sort(employees);
+
+    assertEquals(employees, employeesSortedByDateAsc);
+  }
+
+  @Test
+  public void givenEmpList_SortEmpList_thenCheckSortedList() {
+
+    Collections.sort(employees, new Comparator<Employee>() {
+      public int compare(Employee o1, Employee o2) {
+        return o1.getJoiningDate().compareTo(o2.getJoiningDate());
+      }
+    });
+
+    assertEquals(employees, employeesSortedByDateAsc);
+  }
+
+  @Test
+  public void givenEmpList_SortEmpList_thenCheckSortedListV1() {
+
+    Collections.sort(employees, new Comparator<Employee>() {
+      public int compare(Employee emp1, Employee emp2) {
+        if (emp1.getJoiningDate() == null || emp2.getJoiningDate() == null)
+          return 0;
+        return emp1.getJoiningDate().compareTo(emp2.getJoiningDate());
+      }
+    });
+
+    assertEquals(employees, employeesSortedByDateAsc);
+  }
+
+  @Test
+  public void givenEmpList_SortEmpList_thenSortedListinAscOrder() {
+    Collections.sort(employees, Collections.reverseOrder());
+
+    assertEquals(employees, employeesSortedByDateDesc);
+  }
+
+  @Test
+  public void givenEmpList_SortEmpList_thenCheckSortedListAsc() {
+
+    Collections.sort(employees, new Comparator<Employee>() {
+      public int compare(Employee emp1, Employee emp2) {
+        return emp2.getJoiningDate().compareTo(emp1.getJoiningDate());
+      }
+    });
+
+    assertEquals(employees, employeesSortedByDateDesc);
+  }
+
+  @Test
+  public void givenEmpList_SortEmpList_thenCheckSortedListAscV1() {
+
+    Collections.sort(employees, new Comparator<Employee>() {
+      public int compare(Employee emp1, Employee emp2) {
+        if (emp1.getJoiningDate() == null || emp2.getJoiningDate() == null)
+          return 0;
+        return emp2.getJoiningDate().compareTo(emp1.getJoiningDate());
+      }
+    });
+
+    assertEquals(employees, employeesSortedByDateDesc);
+  }
+
+  @Test
+  public void givenEmpList_SortEmpList_thenCheckSortedListDescLambda() {
+
+    Collections.sort(employees,
+      (emp1, emp2) -> emp2.getJoiningDate().compareTo(emp1.getJoiningDate()));
+
+    assertEquals(employees, employeesSortedByDateDesc);
+  }
+
+  @Test
+  public void givenEmpList_SortEmpList_thenCheckSortedListDescLambdaV1() {
+
+    Collections.sort(employees, (emp1, emp2) -> {
+      if (emp1.getJoiningDate() == null || emp2.getJoiningDate() == null)
+        return 0;
+      return emp2.getJoiningDate().compareTo(emp1.getJoiningDate());
+    });
+
+    assertEquals(employees, employeesSortedByDateDesc);
+  }
+
+  @Test
+  public void givenEmpList_SortEmpList_thenCheckSortedListAscLambda() {
+    Collections.sort(employees,
+      Comparator.comparing(Employee::getJoiningDate));
+    assertEquals(employees, employeesSortedByDateAsc);
+  }
+
+}

core-java-modules/core-java-collections-list-4/README.md

@@ -0,0 +1,7 @@
+## Core Java Collections List (Part 4)
+
+This module contains articles about the Java List collection
+
+### Relevant Articles: 
+- [Working With a List of Lists in Java](https://www.baeldung.com/java-list-of-lists)
+- [[<-- Prev]](/core-java-modules/core-java-collections-list-3)

core-java-modules/core-java-collections-list-4/pom.xml

@@ -0,0 +1,56 @@
+<?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-collections-list-4</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-collections-list-4</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-collections4</artifactId>
+            <version>${commons-collections4.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>net.sf.trove4j</groupId>
+            <artifactId>trove4j</artifactId>
+            <version>${trove4j.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>it.unimi.dsi</groupId>
+            <artifactId>fastutil</artifactId>
+            <version>${fastutil.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>colt</groupId>
+            <artifactId>colt</artifactId>
+            <version>${colt.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+            <version>${jmh-core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+            <version>${jmh-generator.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <trove4j.version>3.0.2</trove4j.version>
+        <fastutil.version>8.1.0</fastutil.version>
+        <colt.version>1.2.0</colt.version>
+    </properties>
+
+</project>