Merge remote-tracking branch 'upstream/master'

algorithms-miscellaneous-2/README.md

@@ -15,3 +15,5 @@
 - [Calculate Percentage in Java](https://www.baeldung.com/java-calculate-percentage)
 - [Converting Between Byte Arrays and Hexadecimal Strings in Java](https://www.baeldung.com/java-byte-arrays-hex-strings)
 - [Convert Latitude and Longitude to a 2D Point in Java](https://www.baeldung.com/java-convert-latitude-longitude)
+- [Reversing a Binary Tree in Java](https://www.baeldung.com/java-reversing-a-binary-tree)
+- [Find If Two Numbers Are Relatively Prime in Java](https://www.baeldung.com/java-two-relatively-prime-numbers)

core-groovy-2/README.md

@@ -3,5 +3,5 @@
 ## Relevant articles:
 
 - [String Matching in Groovy](http://www.baeldung.com/)
-- [Groovy def Keyword]
-
+- [Groovy def Keyword](https://www.baeldung.com/groovy-def-keyword)
+- [Pattern Matching in Strings in Groovy](https://www.baeldung.com/groovy-pattern-matching)

core-groovy-collections/README.md

@@ -2,5 +2,5 @@
 
 ## Relevant articles:
 
-- [Maps in Groovy](http://www.baeldung.com/)
+- [Maps in Groovy](https://www.baeldung.com/groovy-maps)
 

core-java-arrays/src/main/java/com/baeldung/array/conversions/StreamArrayConversion.java

@@ -0,0 +1,52 @@
+package com.baeldung.array.conversions;
+
+import java.util.Arrays;
+import java.util.function.IntFunction;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+public class StreamArrayConversion {
+
+    public static String[] stringStreamToStringArrayUsingFunctionalInterface(Stream<String> stringStream) {
+        IntFunction<String[]> intFunction = new IntFunction<String[]>() {
+            @Override
+            public String[] apply(int value) {
+                return new String[value];
+            }
+        };
+
+        return stringStream.toArray(intFunction);
+    }
+
+    public static String[] stringStreamToStringArrayUsingMethodReference(Stream<String> stringStream) {
+        return stringStream.toArray(String[]::new);
+    }
+
+    public static String[] stringStreamToStringArrayUsingLambda(Stream<String> stringStream) {
+        return stringStream.toArray(value -> new String[value]);
+    }
+
+    public static Integer[] integerStreamToIntegerArray(Stream<Integer> integerStream) {
+        return integerStream.toArray(Integer[]::new);
+    }
+
+    public static int[] intStreamToPrimitiveIntArray(Stream<Integer> integerStream) {
+        return integerStream.mapToInt(i -> i).toArray();
+    }
+
+    public static Stream<String> stringArrayToStreamUsingArraysStream(String[] stringArray) {
+        return Arrays.stream(stringArray);
+    }
+
+    public static Stream<String> stringArrayToStreamUsingStreamOf(String[] stringArray) {
+        return Stream.of(stringArray);
+    }
+
+    public static IntStream primitiveIntArrayToStreamUsingArraysStream(int[] intArray) {
+        return Arrays.stream(intArray);
+    }
+
+    public static Stream<int[]> primitiveIntArrayToStreamUsingStreamOf(int[] intArray) {
+        return Stream.of(intArray);
+    }
+}

core-java-arrays/src/test/java/com/baeldung/array/conversions/StreamArrayConversionUnitTest.java

@@ -0,0 +1,70 @@
+package com.baeldung.array.conversions;
+
+import static com.baeldung.array.conversions.StreamArrayConversion.intStreamToPrimitiveIntArray;
+import static com.baeldung.array.conversions.StreamArrayConversion.integerStreamToIntegerArray;
+import static com.baeldung.array.conversions.StreamArrayConversion.stringStreamToStringArrayUsingFunctionalInterface;
+import static com.baeldung.array.conversions.StreamArrayConversion.stringStreamToStringArrayUsingLambda;
+import static com.baeldung.array.conversions.StreamArrayConversion.stringStreamToStringArrayUsingMethodReference;
+import static com.baeldung.array.conversions.StreamArrayConversion.stringArrayToStreamUsingArraysStream;
+import static com.baeldung.array.conversions.StreamArrayConversion.stringArrayToStreamUsingStreamOf;
+import static com.baeldung.array.conversions.StreamArrayConversion.primitiveIntArrayToStreamUsingArraysStream;
+import static com.baeldung.array.conversions.StreamArrayConversion.primitiveIntArrayToStreamUsingStreamOf;
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import com.google.common.collect.Iterators;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+import org.junit.Test;
+
+public class StreamArrayConversionUnitTest {
+
+    private String[] stringArray = new String[]{"baeldung", "convert", "to", "string", "array"};
+    private Integer[] integerArray = new Integer[]{1, 2, 3, 4, 5, 6, 7};
+    private int[] intPrimitiveArray = new int[]{1, 2, 3, 4, 5, 6, 7};
+
+    @Test
+    public void givenStringStream_thenConvertToStringArrayUsingFunctionalInterface() {
+        Stream<String> stringStream = Stream.of("baeldung", "convert", "to", "string", "array");
+        assertArrayEquals(stringArray, stringStreamToStringArrayUsingFunctionalInterface(stringStream));
+    }
+
+    @Test
+    public void givenStringStream_thenConvertToStringArrayUsingMethodReference() {
+        Stream<String> stringStream = Stream.of("baeldung", "convert", "to", "string", "array");
+        assertArrayEquals(stringArray, stringStreamToStringArrayUsingMethodReference(stringStream));
+    }
+
+    @Test
+    public void givenStringStream_thenConvertToStringArrayUsingLambda() {
+        Stream<String> stringStream = Stream.of("baeldung", "convert", "to", "string", "array");
+        assertArrayEquals(stringArray, stringStreamToStringArrayUsingLambda(stringStream));
+    }
+
+    @Test
+    public void givenIntegerStream_thenConvertToIntegerArray() {
+        Stream<Integer> integerStream = Stream.of(1, 2, 3, 4, 5, 6, 7);
+        assertArrayEquals(integerArray, integerStreamToIntegerArray(integerStream));
+    }
+
+    @Test
+    public void givenIntStream_thenConvertToIntegerArray() {
+        Stream<Integer> integerStream = IntStream.rangeClosed(1, 7).boxed();
+        assertArrayEquals(intPrimitiveArray, intStreamToPrimitiveIntArray(integerStream));
+    }
+
+    @Test
+    public void givenStringArray_whenConvertedTwoWays_thenConvertedStreamsAreEqual() {
+        assertTrue(Iterators
+            .elementsEqual(stringArrayToStreamUsingArraysStream(stringArray).iterator(),
+                stringArrayToStreamUsingStreamOf(stringArray).iterator()));
+    }
+
+    @Test
+    public void givenPrimitiveArray_whenConvertedTwoWays_thenConvertedStreamsAreNotEqual() {
+        assertFalse(Iterators.elementsEqual(
+            primitiveIntArrayToStreamUsingArraysStream(intPrimitiveArray).iterator(),
+            primitiveIntArrayToStreamUsingStreamOf(intPrimitiveArray).iterator()));
+    }
+}

core-java-lambdas/README.md

@@ -0,0 +1,2 @@
+### Relevant Articles:
+- [Java 9 java.lang.Module API](https://www.baeldung.com/java-lambda-effectively-final-local-variables)

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

@@ -7,3 +7,4 @@
 - [Exploring the New HTTP Client in Java 9 and 11](https://www.baeldung.com/java-9-http-client)
 - [An Introduction to Epsilon GC: A No-Op Experimental Garbage Collector](https://www.baeldung.com/jvm-epsilon-gc-garbage-collector)
 - [Guide to jlink](https://www.baeldung.com/jlink)
+- [Transforming an Empty String into an Empty Optional](https://www.baeldung.com/java-empty-string-to-empty-optional)

core-java-modules/core-java-8/src/test/java/com/baeldung/java8/optional/OptionalChainingUnitTest.java

@@ -101,7 +101,7 @@ public class OptionalChainingUnitTest {
     }
 
     private Optional<String> createOptional(String input) {
-        if (input == null || input == "" || input == "empty") {
+        if (input == null || "".equals(input) || "empty".equals(input)) {
             return Optional.empty();
         }
 

core-java-modules/core-java-9/README.md

@@ -21,5 +21,14 @@
 - [Ahead of Time Compilation (AoT)](https://www.baeldung.com/ahead-of-time-compilation)
 - [Java 9 Process API Improvements](https://www.baeldung.com/java-9-process-api)
 - [Guide to java.lang.Process API](https://www.baeldung.com/java-process-api)
-
+- [Java 9 java.util.Objects Additions](https://www.baeldung.com/java-9-objects-new)
+- [Java 9 Reactive Streams](https://www.baeldung.com/java-9-reactive-streams)
+- [Java 9 Optional API Additions](https://www.baeldung.com/java-9-optional)
+- [Java 9 CompletableFuture API Improvements](https://www.baeldung.com/java-9-completablefuture)
+- [Introduction to Java 9 StackWalking API](https://www.baeldung.com/java-9-stackwalking-api)
+- [Java 9 Convenience Factory Methods for Collections](https://www.baeldung.com/java-9-collections-factory-methods)
+- [Java 9 Stream API Improvements](https://www.baeldung.com/java-9-stream-api)
+- [A Guide to Java 9 Modularity](https://www.baeldung.com/java-9-modularity)
+- [Java 9 Platform Module API](https://www.baeldung.com/java-9-module-api)
+- [Java 9 Platform Logging API](https://www.baeldung.com/java-9-logging-api)
 

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

@@ -8,4 +8,5 @@
 - [A Guide to HashSet in Java](http://www.baeldung.com/java-hashset)
 - [A Guide to TreeSet in Java](http://www.baeldung.com/java-tree-set)
 - [Initializing HashSet at the Time of Construction](http://www.baeldung.com/java-initialize-hashset)
-- [Guide to EnumSet](https://www.baeldung.com/java-enumset)
+- [Guide to EnumSet](https://www.baeldung.com/java-enumset)
+- [Set Operations in Java](https://www.baeldung.com/java-set-operations)

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

@@ -0,0 +1,26 @@
+<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.exception.numberformat</groupId>
+    <artifactId>core-java-exceptions</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>core-java-exceptions</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.12</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+</project>

core-java-modules/core-java-exceptions/src/test/java/com/baeldung/exception/numberformat/NumberFormatExceptionUnitTest.java

@@ -0,0 +1,154 @@
+package com.baeldung.exception.numberformat;
+
+import static org.junit.Assert.assertEquals;
+
+import java.math.BigDecimal;
+import java.math.BigInteger;
+import java.text.NumberFormat;
+import java.text.ParseException;
+import java.util.Locale;
+import java.util.logging.Logger;
+
+import org.junit.Test;
+
+/**
+ * A set of examples tested to show cases where NumberFormatException is thrown and not thrown.
+ */
+public class NumberFormatExceptionUnitTest {
+
+    Logger LOG = Logger.getLogger(NumberFormatExceptionUnitTest.class.getName());
+
+    /* ---INTEGER FAIL CASES--- */
+    @Test(expected = NumberFormatException.class)
+    public void givenByteConstructor_whenAlphabetAsInput_thenFail() {
+        Byte byteInt = new Byte("one");
+    }
+
+    @Test(expected = NumberFormatException.class)
+    public void givenShortConstructor_whenSpaceInInput_thenFail() {
+        Short shortInt = new Short("2 ");
+    }
+
+    @Test(expected = NumberFormatException.class)
+    public void givenParseIntMethod_whenSpaceInInput_thenFail() {
+        Integer aIntPrim = Integer.parseInt("6000 ");
+    }
+
+    @Test(expected = NumberFormatException.class)
+    public void givenParseIntMethod_whenUnderscoreInInput_thenFail() {
+        int bIntPrim = Integer.parseInt("6_000");
+    }
+
+    @Test(expected = NumberFormatException.class)
+    public void givenIntegerValueOfMethod_whenCommaInInput_thenFail() {
+        Integer cIntPrim = Integer.valueOf("6,000");
+    }
+
+    @Test(expected = NumberFormatException.class)
+    public void givenBigIntegerConstructor_whenDecimalInInput_thenFail() {
+        BigInteger bigInteger = new BigInteger("4.0");
+    }
+
+    @Test(expected = NumberFormatException.class)
+    public void givenDecodeMethod_whenAlphabetInInput_thenFail() {
+        Long decodeInteger = Long.decode("64403L");
+    }
+
+    /* ---INTEGER PASS CASES--- */
+    @Test
+    public void givenInvalidNumberInputs_whenOptimized_thenPass() {
+        Byte byteInt = new Byte("1");
+        assertEquals(1, byteInt.intValue());
+
+        Short shortInt = new Short("2 ".trim());
+        assertEquals(2, shortInt.intValue());
+
+        Integer aIntObj = Integer.valueOf("6");
+        assertEquals(6, aIntObj.intValue());
+
+        BigInteger bigInteger = new BigInteger("4");
+        assertEquals(4, bigInteger.intValue());
+
+        int aIntPrim = Integer.parseInt("6000 ".trim());
+        assertEquals(6000, aIntPrim);
+
+        int bIntPrim = Integer.parseInt("6_000".replaceAll("_", ""));
+        assertEquals(6000, bIntPrim);
+
+        int cIntPrim = Integer.parseInt("-6000");
+        assertEquals(-6000, cIntPrim);
+
+        Long decodeInteger = Long.decode("644032334");
+        assertEquals(644032334L, decodeInteger.longValue());
+    }
+
+    /* ---DOUBLE FAIL CASES--- */
+    @Test(expected = NumberFormatException.class)
+    public void givenFloatConstructor_whenAlphabetInInput_thenFail() {
+        Float floatDecimalObj = new Float("one.1");
+    }
+
+    @Test(expected = NumberFormatException.class)
+    public void givenDoubleConstructor_whenAlphabetInInput_thenFail() {
+        Double doubleDecimalObj = new Double("two.2");
+    }
+
+    @Test(expected = NumberFormatException.class)
+    public void givenBigDecimalConstructor_whenSpecialCharsInInput_thenFail() {
+        BigDecimal bigDecimalObj = new BigDecimal("3_0.3");
+    }
+
+    @Test(expected = NumberFormatException.class)
+    public void givenParseDoubleMethod_whenCommaInInput_thenFail() {
+        double aDoublePrim = Double.parseDouble("4000,1");
+    }
+
+    /* ---DOUBLE PASS CASES--- */
+    @Test
+    public void givenDoubleConstructor_whenDecimalInInput_thenPass() {
+        Double doubleDecimalObj = new Double("2.2");
+        assertEquals(2.2, doubleDecimalObj.doubleValue(), 0);
+    }
+
+    @Test
+    public void givenDoubleValueOfMethod_whenMinusInInput_thenPass() {
+        Double aDoubleObj = Double.valueOf("-6000");
+        assertEquals(-6000, aDoubleObj.doubleValue(), 0);
+    }
+
+    @Test
+    public void givenUsDecimalNumber_whenParsedWithNumberFormat_thenPass() throws ParseException {
+        Number parsedNumber = parseNumberWithLocale("4000.1", Locale.US);
+        assertEquals(4000.1, parsedNumber);
+        assertEquals(4000.1, parsedNumber.doubleValue(), 0);
+        assertEquals(4000, parsedNumber.intValue());
+    }
+
+    /**
+     * In most European countries (for example, France), comma is used as decimal in place of period.
+     * @throws ParseException if the input string contains special characters other than comma or decimal. 
+     * In this test case, anything after decimal (period) is dropped when a European locale is set.
+     */
+    @Test
+    public void givenEuDecimalNumberHasComma_whenParsedWithNumberFormat_thenPass() throws ParseException {
+        Number parsedNumber = parseNumberWithLocale("4000,1", Locale.FRANCE);
+        LOG.info("Number parsed is: " + parsedNumber);
+        assertEquals(4000.1, parsedNumber);
+        assertEquals(4000.1, parsedNumber.doubleValue(), 0);
+        assertEquals(4000, parsedNumber.intValue());
+    }
+
+    /**
+     * Converts a string into a number retaining all decimals, and symbols valid in a locale.
+     * @param number the input string for a number.
+     * @param locale the locale to consider while parsing a number.
+     * @return the generic number object which can represent multiple number types.
+     * @throws ParseException when input contains invalid characters.
+     */
+    private Number parseNumberWithLocale(String number, Locale locale) throws ParseException {
+        locale = locale == null ? Locale.getDefault() : locale;
+        NumberFormat numberFormat = NumberFormat.getInstance(locale);
+        return numberFormat.parse(number);
+    }
+
+}

core-java-modules/core-java-lang-oop-2/README.md

@@ -4,3 +4,5 @@
 
 ### Relevant Articles: 
 - [Generic Constructors in Java](https://www.baeldung.com/java-generic-constructors)
+- [Cannot Reference “X” Before Supertype Constructor Has Been Called](https://www.baeldung.com/java-cannot-reference-x-before-supertype-constructor-error)
+- [Anonymous Classes in Java](https://www.baeldung.com/java-anonymous-classes)

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

@@ -454,7 +454,7 @@
         <gson.version>2.8.2</gson.version>
 
         <!-- util -->
-        <commons-lang3.version>3.5</commons-lang3.version>
+        <commons-lang3.version>3.9</commons-lang3.version>
         <commons-io.version>2.5</commons-io.version>
         <commons-math3.version>3.6.1</commons-math3.version>
         <decimal4j.version>1.0.3</decimal4j.version>

core-java-modules/core-java/src/main/java/com/baeldung/exceptions/RootCauseFinder.java

@@ -0,0 +1,98 @@
+package com.baeldung.exceptions;
+
+import java.time.LocalDate;
+import java.time.Period;
+import java.time.format.DateTimeParseException;
+import java.util.Objects;
+
+/**
+ * Utility class to find root cause exceptions.
+ */
+public class RootCauseFinder {
+
+    private RootCauseFinder() {
+    }
+
+    public static Throwable findCauseUsingPlainJava(Throwable throwable) {
+        Objects.requireNonNull(throwable);
+        Throwable rootCause = throwable;
+        while (rootCause.getCause() != null && rootCause.getCause() != rootCause) {
+            rootCause = rootCause.getCause();
+        }
+        return rootCause;
+    }
+
+    /**
+     *  Calculates the age of a person from a given date.
+     */
+    static class AgeCalculator {
+
+        private AgeCalculator() {
+        }
+
+        public static int calculateAge(String birthDate) {
+            if (birthDate == null || birthDate.isEmpty()) {
+                throw new IllegalArgumentException();
+            }
+
+            try {
+                return Period
+                  .between(parseDate(birthDate), LocalDate.now())
+                  .getYears();
+            } catch (DateParseException ex) {
+                throw new CalculationException(ex);
+            }
+        }
+
+        private static LocalDate parseDate(String birthDateAsString) {
+
+            LocalDate birthDate;
+            try {
+                birthDate = LocalDate.parse(birthDateAsString);
+            } catch (DateTimeParseException ex) {
+                throw new InvalidFormatException(birthDateAsString, ex);
+            }
+
+            if (birthDate.isAfter(LocalDate.now())) {
+                throw new DateOutOfRangeException(birthDateAsString);
+            }
+
+            return birthDate;
+        }
+
+    }
+
+    static class CalculationException extends RuntimeException {
+
+        CalculationException(DateParseException ex) {
+            super(ex);
+        }
+    }
+
+    static class DateParseException extends RuntimeException {
+
+        DateParseException(String input) {
+            super(input);
+        }
+
+        DateParseException(String input, Throwable thr) {
+            super(input, thr);
+        }
+    }
+
+    static class InvalidFormatException extends DateParseException {
+
+        InvalidFormatException(String input, Throwable thr) {
+            super("Invalid date format: " + input, thr);
+        }
+    }
+
+    static class DateOutOfRangeException extends DateParseException {
+
+        DateOutOfRangeException(String date) {
+            super("Date out of range: " + date);
+        }
+
+    }
+
+}

core-java-modules/core-java/src/test/java/com/baeldung/exceptions/RootCauseFinderUnitTest.java

@@ -0,0 +1,114 @@
+package com.baeldung.exceptions;
+
+import com.google.common.base.Throwables;
+import org.apache.commons.lang3.exception.ExceptionUtils;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.time.LocalDate;
+import java.time.format.DateTimeParseException;
+import java.time.temporal.ChronoUnit;
+
+import static com.baeldung.exceptions.RootCauseFinder.*;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Tests the {@link RootCauseFinder}.
+ */
+public class RootCauseFinderUnitTest {
+
+    @Test
+    public void givenBirthDate_whenCalculatingAge_thenAgeReturned() {
+        try {
+            int age = AgeCalculator.calculateAge("1990-01-01");
+            Assertions.assertEquals(1990, LocalDate
+              .now()
+              .minus(age, ChronoUnit.YEARS)
+              .getYear());
+        } catch (CalculationException e) {
+            Assertions.fail(e.getMessage());
+        }
+    }
+
+    @Test
+    public void givenWrongFormatDate_whenFindingRootCauseUsingJava_thenRootCauseFound() {
+        try {
+            AgeCalculator.calculateAge("010102");
+        } catch (CalculationException ex) {
+            assertTrue(findCauseUsingPlainJava(ex) instanceof DateTimeParseException);
+        }
+    }
+
+    @Test
+    public void givenOutOfRangeDate_whenFindingRootCauseUsingJava_thenRootCauseFound() {
+        try {
+            AgeCalculator.calculateAge("2020-04-04");
+        } catch (CalculationException ex) {
+            assertTrue(findCauseUsingPlainJava(ex) instanceof DateOutOfRangeException);
+        }
+    }
+
+    @Test
+    public void givenNullDate_whenFindingRootCauseUsingJava_thenRootCauseFound() {
+        try {
+            AgeCalculator.calculateAge(null);
+        } catch (Exception ex) {
+            assertTrue(findCauseUsingPlainJava(ex) instanceof IllegalArgumentException);
+        }
+    }
+
+    @Test
+    public void givenWrongFormatDate_whenFindingRootCauseUsingApacheCommons_thenRootCauseFound() {
+        try {
+            AgeCalculator.calculateAge("010102");
+        } catch (CalculationException ex) {
+            assertTrue(ExceptionUtils.getRootCause(ex) instanceof DateTimeParseException);
+        }
+    }
+
+    @Test
+    public void givenOutOfRangeDate_whenFindingRootCauseUsingApacheCommons_thenRootCauseFound() {
+        try {
+            AgeCalculator.calculateAge("2020-04-04");
+        } catch (CalculationException ex) {
+            assertTrue(ExceptionUtils.getRootCause(ex) instanceof DateOutOfRangeException);
+        }
+    }
+
+    @Test
+    public void givenNullDate_whenFindingRootCauseUsingApacheCommons_thenRootCauseNotFound() {
+        try {
+            AgeCalculator.calculateAge(null);
+        } catch (Exception ex) {
+            assertTrue(ExceptionUtils.getRootCause(ex) instanceof IllegalArgumentException);
+        }
+    }
+
+    @Test
+    public void givenWrongFormatDate_whenFindingRootCauseUsingGuava_thenRootCauseFound() {
+        try {
+            AgeCalculator.calculateAge("010102");
+        } catch (CalculationException ex) {
+            assertTrue(Throwables.getRootCause(ex) instanceof DateTimeParseException);
+        }
+    }
+
+    @Test
+    public void givenOutOfRangeDate_whenFindingRootCauseUsingGuava_thenRootCauseFound() {
+        try {
+            AgeCalculator.calculateAge("2020-04-04");
+        } catch (CalculationException ex) {
+            assertTrue(Throwables.getRootCause(ex) instanceof DateOutOfRangeException);
+        }
+    }
+
+    @Test
+    public void givenNullDate_whenFindingRootCauseUsingGuava_thenRootCauseFound() {
+        try {
+            AgeCalculator.calculateAge(null);
+        } catch (Exception ex) {
+            assertTrue(Throwables.getRootCause(ex) instanceof IllegalArgumentException);
+        }
+    }
+
+}

core-java-modules/pom.xml

@@ -15,6 +15,7 @@
 
     <modules>
         <module>pre-jpms</module>
+        <module>core-java-exceptions</module>
     </modules>
     
 </project>

core-kotlin-2/README.md

@@ -6,4 +6,5 @@
 - [Kotlin Scope Functions](https://www.baeldung.com/kotlin-scope-functions)
 - [Kotlin Annotations](https://www.baeldung.com/kotlin-annotations)
 - [Split a List into Parts in Kotlin](https://www.baeldung.com/kotlin-split-list-into-parts)
-- [String Comparison in Kotlin](https://www.baeldung.com/kotlin-string-comparison)
+- [String Comparison in Kotlin](https://www.baeldung.com/kotlin-string-comparison)
+- [Guide to JVM Platform Annotations in Kotlin](https://www.baeldung.com/kotlin-jvm-annotations)

guava-collections-set/README.md

@@ -0,0 +1,4 @@
+
+### Relevant Articles: 
+
+- [Guide to Guava Multiset](https://www.baeldung.com/guava-multiset)

jackson-2/README.md

@@ -7,4 +7,6 @@ The "REST With Spring" Classes: http://bit.ly/restwithspring
 
 ### Relevant Articles: 
 - [Mapping Multiple JSON Fields to a Single Java Field](https://www.baeldung.com/json-multiple-fields-single-java-field)
+- [How to Process YAML with Jackson](https://www.baeldung.com/jackson-yaml)
 - [Working with Tree Model Nodes in Jackson](https://www.baeldung.com/jackson-json-node-tree-model)
+

java-collections-maps-2/README.md

@@ -1,2 +1,3 @@
 ## Relevant Articles:
 - [Map of Primitives in Java](https://www.baeldung.com/java-map-primitives)
+- [Copying a HashMap in Java](https://www.baeldung.com/java-copy-hashmap)

java-strings-2/src/main/java/com/baeldung/localization/App.java

@@ -0,0 +1,21 @@
+package com.baeldung.localization;
+
+import java.text.ParseException;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Locale;
+
+public class App {
+
+    /**
+     * Runs all available formatter
+     * @throws ParseException 
+     */
+    public static void main(String[] args) {
+        List<Locale> locales = Arrays.asList(new Locale[] { Locale.UK, Locale.ITALY, Locale.FRANCE, Locale.forLanguageTag("pl-PL") });
+        Localization.run(locales);
+        JavaSEFormat.run(locales);
+        ICUFormat.run(locales);
+    }
+
+}

java-strings-2/src/main/java/com/baeldung/localization/ICUFormat.java

@@ -0,0 +1,29 @@
+package com.baeldung.localization;
+
+import java.util.List;
+import java.util.Locale;
+import java.util.ResourceBundle;
+
+import com.ibm.icu.text.MessageFormat;
+
+public class ICUFormat {
+
+    public static String getLabel(Locale locale, Object[] data) {
+        ResourceBundle bundle = ResourceBundle.getBundle("formats", locale);
+        String format = bundle.getString("label-icu");
+        MessageFormat formatter = new MessageFormat(format, locale);
+        return formatter.format(data);
+    }
+
+    public static void run(List<Locale> locales) {
+        System.out.println("ICU formatter");
+        locales.forEach(locale -> System.out.println(getLabel(locale, new Object[] { "Alice", "female", 0 })));
+        locales.forEach(locale -> System.out.println(getLabel(locale, new Object[] { "Alice", "female", 1 })));
+        locales.forEach(locale -> System.out.println(getLabel(locale, new Object[] { "Alice", "female", 2 })));
+        locales.forEach(locale -> System.out.println(getLabel(locale, new Object[] { "Alice", "female", 3 })));
+        locales.forEach(locale -> System.out.println(getLabel(locale, new Object[] { "Bob", "male", 0 })));
+        locales.forEach(locale -> System.out.println(getLabel(locale, new Object[] { "Bob", "male", 1 })));
+        locales.forEach(locale -> System.out.println(getLabel(locale, new Object[] { "Bob", "male", 2 })));
+        locales.forEach(locale -> System.out.println(getLabel(locale, new Object[] { "Bob", "male", 3 })));
+    }
+}

java-strings-2/src/main/java/com/baeldung/localization/JavaSEFormat.java

@@ -0,0 +1,24 @@
+package com.baeldung.localization;
+
+import java.text.MessageFormat;
+import java.util.Date;
+import java.util.List;
+import java.util.Locale;
+import java.util.ResourceBundle;
+
+public class JavaSEFormat {
+
+    public static String getLabel(Locale locale, Object[] data) {
+        ResourceBundle bundle = ResourceBundle.getBundle("formats", locale);
+        final String pattern = bundle.getString("label");
+        final MessageFormat formatter = new MessageFormat(pattern, locale);
+        return formatter.format(data);
+    }
+
+    public static void run(List<Locale> locales) {
+        System.out.println("Java formatter");
+        final Date date = new Date(System.currentTimeMillis());
+        locales.forEach(locale -> System.out.println(getLabel(locale, new Object[] { date, "Alice", 0 })));
+        locales.forEach(locale -> System.out.println(getLabel(locale, new Object[] { date, "Alice", 2 })));
+    }
+}

java-strings-2/src/main/java/com/baeldung/localization/Localization.java

@@ -0,0 +1,18 @@
+package com.baeldung.localization;
+
+import java.util.List;
+import java.util.Locale;
+import java.util.ResourceBundle;
+
+public class Localization {
+
+    public static String getLabel(Locale locale) {
+        final ResourceBundle bundle = ResourceBundle.getBundle("messages", locale);
+        return bundle.getString("label");
+    }
+
+    public static void run(List<Locale> locales) {
+        locales.forEach(locale -> System.out.println(getLabel(locale)));
+    }
+
+}

java-strings-2/src/main/resources/formats_en.properties

@@ -0,0 +1,2 @@
+label=On {0, date, short} {1} has sent you {2, choice, 0#no messages|1#a message|2#two messages|2<{2,number,integer} messages}.
+label-icu={0} has sent you {2, plural, =0 {no messages} =1 {a message} other {{2, number, integer} messages}}.

java-strings-2/src/main/resources/formats_fr.properties

@@ -0,0 +1,2 @@
+label={0, date, short}, {1}{2, choice, 0# ne|0<} vous a envoy\u00e9 {2, choice, 0#aucun message|1#un message|2#deux messages|2<{2,number,integer} messages}.
+label-icu={0} {2, plural, =0 {ne } other {}}vous a envoy\u00e9 {2, plural, =0 {aucun message} =1 {un message} other {{2, number, integer} messages}}.

java-strings-2/src/main/resources/formats_it.properties

@@ -0,0 +1,2 @@
+label={0, date, short} {1} ti ha inviato {2, choice, 0#nessun messagio|1#un messaggio|2#due messaggi|2<{2, number, integer} messaggi}.
+label-icu={0} {2, plural, =0 {non } other {}}ti ha inviato {2, plural, =0 {nessun messaggio} =1 {un messaggio} other {{2, number, integer} messaggi}}.

java-strings-2/src/main/resources/formats_pl.properties

@@ -0,0 +1,2 @@
+label=W {0, date, short} {1}{2, choice, 0# nie|0<} wys\u0142a\u0142a ci {2, choice, 0#\u017Cadnych wiadomo\u015Bci|1#wiadomo\u015B\u0107|2#dwie wiadomo\u015Bci|2<{2, number, integer} wiadomo\u015Bci}.
+label-icu={0} {2, plural, =0 {nie } other {}}{1, select, male {wys\u0142a\u0142} female {wys\u0142a\u0142a} other {wys\u0142a\u0142o}} ci {2, plural, =0 {\u017Cadnej wiadomo\u015Bci} =1 {wiadomo\u015B\u0107} other {{2, number, integer} wiadomo\u015Bci}}.

java-strings-2/src/main/resources/messages_en.properties

@@ -0,0 +1 @@
+label=Alice has sent you a message.