Merge branch 'eugenp:master' into master

core-java-modules/core-java-arrays-operations-basic/src/main/java/com/baeldung/arrayindex/ArrayIndex.java

@@ -0,0 +1,28 @@
+package com.baeldung.arrayindex;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.IntStream;
+
+class ArrayIndex {
+    static int forLoop(int[] numbers, int target) {
+        for (int index = 0; index < numbers.length; index++) {
+            if (numbers[index] == target) {
+                return index;
+            }
+        }
+        return -1;
+    }
+
+    static int listIndexOf(Integer[] numbers, int target) {
+        List<Integer> list = Arrays.asList(numbers);
+        return list.indexOf(target);
+    }
+
+    static int intStream(int[] numbers, int target) {
+        return IntStream.range(0, numbers.length)
+          .filter(i -> numbers[i] == target)
+          .findFirst()
+          .orElse(-1);
+    }
+}

core-java-modules/core-java-arrays-operations-basic/src/test/java/com/baeldung/arrayindex/ArrayIndexUnitTest.java

@@ -0,0 +1,106 @@
+package com.baeldung.arrayindex;
+
+import static com.baeldung.arrayindex.ArrayIndex.forLoop;
+import static com.baeldung.arrayindex.ArrayIndex.intStream;
+import static com.baeldung.arrayindex.ArrayIndex.listIndexOf;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Arrays;
+
+import org.apache.commons.lang3.ArrayUtils;
+import org.junit.jupiter.api.Test;
+
+import com.google.common.primitives.Ints;
+
+class ArrayIndexUnitTest {
+
+    @Test
+    void givenIntegerArray_whenUseForLoop_thenWillGetElementIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(2, forLoop(numbers, 30));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseForLoop_thenWillGetElementMinusOneIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, forLoop(numbers, 100));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseIndexOf_thenWillGetElementIndex() {
+        Integer[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(2, listIndexOf(numbers, 30));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseIndexOf_thenWillGetElementMinusOneIndex() {
+        Integer[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, listIndexOf(numbers, 100));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseIntStream_thenWillGetElementIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(2, intStream(numbers, 30));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseIntStream_thenWillGetElementMinusOneIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, intStream(numbers, 100));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseBinarySearch_thenWillGetElementIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(2, Arrays.binarySearch(numbers, 30));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseBinarySearch_thenWillGetUpperBoundMinusIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-6, Arrays.binarySearch(numbers, 100));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseBinarySearch_thenWillGetInArrayMinusIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-2, Arrays.binarySearch(numbers, 15));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseBinarySearch_thenWillGetLowerBoundMinusIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, Arrays.binarySearch(numbers, -15));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseApacheCommons_thenWillGetElementIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(2, ArrayUtils.indexOf(numbers, 30));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseApacheCommonsStartingFromIndex_thenWillGetNegativeIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, ArrayUtils.indexOf(numbers, 30, 3));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseApacheCommons_thenWillGetElementMinusOneIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, ArrayUtils.indexOf(numbers, 100));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseGuavaInts_thenWillGetElementIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(2, Ints.indexOf(numbers, 30));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseGuavaInts_thenWillGetElementMinusOneIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, Ints.indexOf(numbers, 100));
+    }
+}

core-java-modules/core-java-char/src/test/java/com/baeldung/charandstring/DifferenceBetweenCharAndStringUnitTest.java

@@ -0,0 +1,56 @@
+package com.baeldung.charandstring;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+
+import org.junit.jupiter.api.Test;
+
+public class DifferenceBetweenCharAndStringUnitTest {
+
+    @Test
+    void whenPlusTwoChars_thenGetSumAsInteger() {
+        char h = 'H'; // the value is 72
+        char i = 'i'; // the value is 105
+        assertEquals(177, h + i);
+        assertInstanceOf(Integer.class, h + i);
+    }
+
+    @Test
+    void whenPlusTwoStrings_thenConcatenateThem() {
+        String i = "i";
+        String h = "H";
+        assertEquals("Hi", h + i);
+    }
+
+    @Test
+    void whenPlusCharsAndStrings_thenGetExpectedValues() {
+        char c = 'C';
+        assertEquals("C", "" + c);
+
+        char h = 'H'; // the value is 72
+        char i = 'i'; // the value is 105
+        assertEquals("Hi", "" + h + i);
+        assertEquals("Hi", h + "" + i);
+        assertEquals("177", h + i + "");
+    }
+
+    @Test
+    void whenStringChars_thenGetCharArray() {
+        char h = 'h';
+        char e = 'e';
+        char l = 'l';
+        char o = 'o';
+
+        String hello = "hello";
+        assertEquals(h, hello.charAt(0));
+        assertEquals(e, hello.charAt(1));
+        assertEquals(l, hello.charAt(2));
+        assertEquals(l, hello.charAt(3));
+        assertEquals(o, hello.charAt(4));
+
+        char[] chars = new char[] { h, e, l, l, o };
+        char[] charsFromString = hello.toCharArray();
+        assertArrayEquals(chars, charsFromString);
+    }
+}

core-java-modules/core-java-io-apis-2/README.md

@@ -6,4 +6,4 @@ This module contains articles about core Java input/output(IO) APIs.
 - [Constructing a Relative Path From Two Absolute Paths in Java](https://www.baeldung.com/java-relative-path-absolute)
 - [Java Scanner Taking a Character Input](https://www.baeldung.com/java-scanner-character-input)
 - [Get the Desktop Path in Java](https://www.baeldung.com/java-desktop-path)
-
+- [Integer.parseInt(scanner.nextLine()) and scanner.nextInt() in Java](https://www.baeldung.com/java-scanner-integer)

core-java-modules/core-java-io-conversions-2/src/test/java/com/baeldung/inputstreamtostring/JavaInputStreamToXUnitTest.java

@@ -49,7 +49,7 @@ public class JavaInputStreamToXUnitTest {
         final InputStream inputStream = new ByteArrayInputStream(originalString.getBytes());
 
         final StringBuilder textBuilder = new StringBuilder();
-        try (Reader reader = new BufferedReader(new InputStreamReader(inputStream, Charset.forName(StandardCharsets.UTF_8.name())))) {
+        try (Reader reader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8))) {
             int c;
             while ((c = reader.read()) != -1) {
                 textBuilder.append((char) c);
@@ -63,7 +63,7 @@ public class JavaInputStreamToXUnitTest {
         final String originalString = randomAlphabetic(DEFAULT_SIZE);
         final InputStream inputStream = new ByteArrayInputStream(originalString.getBytes());
 
-        final String text = new BufferedReader(new InputStreamReader(inputStream, Charset.forName(StandardCharsets.UTF_8.name())))
+        final String text = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8))
           .lines()
           .collect(Collectors.joining("\n"));
 

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

@@ -0,0 +1,7 @@
+## Core Java Lang OOP - Constructors - Part 2
+
+This module contains article about constructors in Java
+
+### Relevant Articles:
+- [Different Ways to Create an Object in Java](https://www.baeldung.com/java-different-ways-to-create-objects)
+- More articles: [[<-- Prev]](/core-java-modules/core-java-lang-oop-constructors)

core-java-modules/core-java-lang-oop-constructors-2/pom.xml

@@ -0,0 +1,16 @@
+<?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-lang-oop-constructors-2</artifactId>
+    <name>core-java-lang-oop-constructors-2</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <artifactId>core-java-modules</artifactId>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+
+</project>

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

@@ -13,4 +13,4 @@ This module contains article about constructors in Java
 - [Constructor Specification in Java](https://www.baeldung.com/java-constructor-specification)
 - [Static vs. Instance Initializer Block in Java](https://www.baeldung.com/java-static-instance-initializer-blocks)
 - [Accessing Private Constructor in Java](https://www.baeldung.com/java-private-constructor-access)
-- [Different Ways to Create an Object in Java](https://www.baeldung.com/java-different-ways-to-create-objects)
+- More articles: [[next -->]](/core-java-modules/core-java-lang-oop-constructors-2)

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

@@ -11,3 +11,4 @@ This module contains articles about methods in Java
 - [The Covariant Return Type in Java](https://www.baeldung.com/java-covariant-return-type)
 - [Does a Method’s Signature Include the Return Type in Java?](https://www.baeldung.com/java-method-signature-return-type)
 - [Solving the Hide Utility Class Public Constructor Sonar Warning](https://www.baeldung.com/java-sonar-hide-implicit-constructor)
+- [Best Practices for Passing Many Arguments to a Method in Java](https://www.baeldung.com/java-best-practices-many-parameters-method)

core-java-modules/core-java-networking-4/README.md

@@ -3,3 +3,4 @@
 - [Validating URL in Java](https://www.baeldung.com/java-validate-url)
 - [Validating IPv4 Address in Java](https://www.baeldung.com/java-validate-ipv4-address)
 - [Download a Webpage in Java](https://www.baeldung.com/java-download-webpage)
+- [URL Query Manipulation in Java](https://www.baeldung.com/java-url-query-manipulation)

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

@@ -13,3 +13,4 @@ This module contains articles about performance of Java applications
 - [Capturing a Java Thread Dump](https://www.baeldung.com/java-thread-dump)
 - [JMX Ports](https://www.baeldung.com/jmx-ports)
 - [Calling JMX MBean Method From a Shell Script](https://www.baeldung.com/jmx-mbean-shell-access)
+- [External Debugging With JMXTerm](https://www.baeldung.com/java-jmxterm-external-debugging)

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

@@ -5,4 +5,5 @@
 - [Converting Camel Case and Title Case to Words in Java](https://www.baeldung.com/java-camel-case-title-case-to-words)
 - [How to Use Regular Expressions to Replace Tokens in Strings in Java](https://www.baeldung.com/java-regex-token-replacement)
 - [Creating a Java Array from Regular Expression Matches](https://www.baeldung.com/java-array-regex-matches)
+- [Getting the Text That Follows After the Regex Match in Java](https://www.baeldung.com/java-regex-text-after-match)
 - More articles: [[<-- prev]](/core-java-modules/core-java-regex)

core-java-modules/core-java-string-algorithms-3/README.md

@@ -10,3 +10,4 @@ This module contains articles about string-related algorithms.
 - [Check if the First Letter of a String is Uppercase](https://www.baeldung.com/java-check-first-letter-uppercase)
 - [Find the First Non Repeating Character in a String in Java](https://www.baeldung.com/java-find-the-first-non-repeating-character)
 - [Find the First Embedded Occurrence of an Integer in a Java String](https://www.baeldung.com/java-string-find-embedded-integer)
+- [Find the Most Frequent Characters in a String](https://www.baeldung.com/java-string-find-most-frequent-characters)

core-java-modules/core-java-string-algorithms/src/main/java/com/baeldung/reverse/ReverseStringExamples.java

@@ -1,5 +1,9 @@
 package com.baeldung.reverse;
 
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
 import org.apache.commons.lang3.StringUtils;
 
 public class ReverseStringExamples {
@@ -46,11 +50,43 @@ public class ReverseStringExamples {
         }
 
         return output.toString()
-            .trim();
+          .trim();
     }
 
     public static String reverseTheOrderOfWordsUsingApacheCommons(String sentence) {
         return StringUtils.reverseDelimited(sentence, ' ');
     }
 
+    public static String reverseUsingIntStreamRangeMethod(String str) {
+        if (str == null) {
+            return null;
+        }
+
+        char[] charArray = str.toCharArray();
+        return IntStream.range(0, str.length())
+          .mapToObj(i -> charArray[str.length() - i - 1])
+          .collect(StringBuilder::new, StringBuilder::append, StringBuilder::append)
+          .toString();
+    }
+
+    public static String reverseUsingStreamOfMethod(String str) {
+        if (str == null) {
+            return null;
+        }
+
+        return Stream.of(str)
+          .map(string -> new StringBuilder(string).reverse())
+          .collect(Collectors.joining());
+    }
+
+    public static String reverseUsingCharsMethod(String str) {
+        if (str == null) {
+            return null;
+        }
+
+        return str.chars()
+          .mapToObj(c -> (char) c)
+          .reduce("", (a, b) -> b + a, (a2, b2) -> b2 + a2);
+    }
+
 }

core-java-modules/core-java-string-algorithms/src/test/java/com/baeldung/reverse/ReverseStringExamplesUnitTest.java

@@ -1,10 +1,11 @@
 package com.baeldung.reverse;
 
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+
 import org.apache.commons.lang3.StringUtils;
 import org.junit.Test;
 
-import static org.junit.Assert.assertEquals;
-
 public class ReverseStringExamplesUnitTest {
 
     private static final String STRING_INPUT = "cat";
@@ -19,7 +20,7 @@ public class ReverseStringExamplesUnitTest {
         String reversedEmpty = ReverseStringExamples.reverse(StringUtils.EMPTY);
 
         assertEquals(STRING_INPUT_REVERSED, reversed);
-        assertEquals(null, reversedNull);
+        assertNull(reversedNull);
         assertEquals(StringUtils.EMPTY, reversedEmpty);
     }
 
@@ -30,7 +31,7 @@ public class ReverseStringExamplesUnitTest {
         String reversedEmpty = ReverseStringExamples.reverseUsingStringBuilder(StringUtils.EMPTY);
 
         assertEquals(STRING_INPUT_REVERSED, reversed);
-        assertEquals(null, reversedNull);
+        assertNull(reversedNull);
         assertEquals(StringUtils.EMPTY, reversedEmpty);
     }
 
@@ -41,7 +42,7 @@ public class ReverseStringExamplesUnitTest {
         String reversedEmpty = ReverseStringExamples.reverseUsingApacheCommons(StringUtils.EMPTY);
 
         assertEquals(STRING_INPUT_REVERSED, reversed);
-        assertEquals(null, reversedNull);
+        assertNull(reversedNull);
         assertEquals(StringUtils.EMPTY, reversedEmpty);
     }
 
@@ -52,7 +53,7 @@ public class ReverseStringExamplesUnitTest {
         String reversedEmpty = ReverseStringExamples.reverseTheOrderOfWords(StringUtils.EMPTY);
 
         assertEquals(REVERSED_WORDS_SENTENCE, reversed);
-        assertEquals(null, reversedNull);
+        assertNull(reversedNull);
         assertEquals(StringUtils.EMPTY, reversedEmpty);
     }
 
@@ -63,7 +64,40 @@ public class ReverseStringExamplesUnitTest {
         String reversedEmpty = ReverseStringExamples.reverseTheOrderOfWordsUsingApacheCommons(StringUtils.EMPTY);
 
         assertEquals(REVERSED_WORDS_SENTENCE, reversed);
-        assertEquals(null, reversedNull);
+        assertNull(reversedNull);
+        assertEquals(StringUtils.EMPTY, reversedEmpty);
+    }
+
+    @Test
+    public void whenReverseStringUsingIntStreamRangeMethod_ThenCorrectStringIsReturned() {
+        String reversed = ReverseStringExamples.reverseUsingIntStreamRangeMethod(STRING_INPUT);
+        String reversedNull = ReverseStringExamples.reverseUsingIntStreamRangeMethod(null);
+        String reversedEmpty = ReverseStringExamples.reverseUsingIntStreamRangeMethod(StringUtils.EMPTY);
+
+        assertEquals(STRING_INPUT_REVERSED, reversed);
+        assertNull(reversedNull);
+        assertEquals(StringUtils.EMPTY, reversedEmpty);
+    }
+
+    @Test
+    public void whenReverseStringUsingCharsMethod_ThenCorrectStringIsReturned() {
+        String reversed = ReverseStringExamples.reverseUsingCharsMethod(STRING_INPUT);
+        String reversedNull = ReverseStringExamples.reverseUsingCharsMethod(null);
+        String reversedEmpty = ReverseStringExamples.reverseUsingCharsMethod(StringUtils.EMPTY);
+
+        assertEquals(STRING_INPUT_REVERSED, reversed);
+        assertNull(reversedNull);
+        assertEquals(StringUtils.EMPTY, reversedEmpty);
+    }
+
+    @Test
+    public void whenReverseStringUsingStreamOfMethod_ThenCorrectStringIsReturned() {
+        String reversed = ReverseStringExamples.reverseUsingStreamOfMethod(STRING_INPUT);
+        String reversedNull = ReverseStringExamples.reverseUsingStreamOfMethod(null);
+        String reversedEmpty = ReverseStringExamples.reverseUsingStreamOfMethod(StringUtils.EMPTY);
+
+        assertEquals(STRING_INPUT_REVERSED, reversed);
+        assertNull(reversedNull);
         assertEquals(StringUtils.EMPTY, reversedEmpty);
     }
 

core-java-modules/core-java-string-operations-5/src/main/java/com/baeldung/firstchardigit/FirstCharDigit.java

@@ -0,0 +1,62 @@
+package com.baeldung.firstchardigit;
+
+import java.util.regex.Pattern;
+
+import com.google.common.base.CharMatcher;
+
+public class FirstCharDigit {
+
+    public static boolean checkUsingCharAtMethod(String str) {
+        if (str == null || str.length() == 0) {
+            return false;
+        }
+
+        char c = str.charAt(0);
+        return c >= '0' && c <= '9';
+    }
+
+    public static boolean checkUsingIsDigitMethod(String str) {
+        if (str == null || str.length() == 0) {
+            return false;
+        }
+
+        return Character.isDigit(str.charAt(0));
+    }
+
+    public static boolean checkUsingPatternClass(String str) {
+        if (str == null || str.length() == 0) {
+            return false;
+        }
+
+        return Pattern.compile("^[0-9].*")
+          .matcher(str)
+          .matches();
+    }
+
+    public static boolean checkUsingMatchesMethod(String str) {
+        if (str == null || str.length() == 0) {
+            return false;
+        }
+
+        return str.matches("^[0-9].*");
+    }
+
+    public static boolean checkUsingCharMatcherInRangeMethod(String str) {
+        if (str == null || str.length() == 0) {
+            return false;
+        }
+
+        return CharMatcher.inRange('0', '9')
+          .matches(str.charAt(0));
+    }
+
+    public static boolean checkUsingCharMatcherForPredicateMethod(String str) {
+        if (str == null || str.length() == 0) {
+            return false;
+        }
+
+        return CharMatcher.forPredicate(Character::isDigit)
+          .matches(str.charAt(0));
+    }
+
+}

core-java-modules/core-java-string-operations-5/src/test/java/com/baeldung/firstchardigit/FirstCharDigitUnitTest.java

@@ -0,0 +1,58 @@
+package com.baeldung.firstchardigit;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+class FirstCharDigitUnitTest {
+
+    @Test
+    void givenString_whenUsingCharAtMethod_thenSuccess() {
+        assertTrue(FirstCharDigit.checkUsingCharAtMethod("12 years"));
+        assertFalse(FirstCharDigit.checkUsingCharAtMethod("years"));
+        assertFalse(FirstCharDigit.checkUsingCharAtMethod(""));
+        assertFalse(FirstCharDigit.checkUsingCharAtMethod(null));
+    }
+
+    @Test
+    void givenString_whenUsingIsDigitMethod_thenSuccess() {
+        assertTrue(FirstCharDigit.checkUsingIsDigitMethod("10 cm"));
+        assertFalse(FirstCharDigit.checkUsingIsDigitMethod("cm"));
+        assertFalse(FirstCharDigit.checkUsingIsDigitMethod(""));
+        assertFalse(FirstCharDigit.checkUsingIsDigitMethod(null));
+    }
+
+    @Test
+    void givenString_whenUsingPatternClass_thenSuccess() {
+        assertTrue(FirstCharDigit.checkUsingPatternClass("1 kg"));
+        assertFalse(FirstCharDigit.checkUsingPatternClass("kg"));
+        assertFalse(FirstCharDigit.checkUsingPatternClass(""));
+        assertFalse(FirstCharDigit.checkUsingPatternClass(null));
+    }
+
+    @Test
+    void givenString_whenUsingMatchesMethod_thenSuccess() {
+        assertTrue(FirstCharDigit.checkUsingMatchesMethod("123"));
+        assertFalse(FirstCharDigit.checkUsingMatchesMethod("ABC"));
+        assertFalse(FirstCharDigit.checkUsingMatchesMethod(""));
+        assertFalse(FirstCharDigit.checkUsingMatchesMethod(null));
+    }
+
+    @Test
+    void givenString_whenUsingCharMatcherInRangeMethod_thenSuccess() {
+        assertTrue(FirstCharDigit.checkUsingCharMatcherInRangeMethod("2023"));
+        assertFalse(FirstCharDigit.checkUsingCharMatcherInRangeMethod("abc"));
+        assertFalse(FirstCharDigit.checkUsingCharMatcherInRangeMethod(""));
+        assertFalse(FirstCharDigit.checkUsingCharMatcherInRangeMethod(null));
+    }
+
+    @Test
+    void givenString_whenUsingCharMatcherForPredicateMethod_thenSuccess() {
+        assertTrue(FirstCharDigit.checkUsingCharMatcherForPredicateMethod("100"));
+        assertFalse(FirstCharDigit.checkUsingCharMatcherForPredicateMethod("abdo"));
+        assertFalse(FirstCharDigit.checkUsingCharMatcherForPredicateMethod(""));
+        assertFalse(FirstCharDigit.checkUsingCharMatcherForPredicateMethod(null));
+    }
+
+}

core-java-modules/core-java-string-operations-5/src/test/java/com/baeldung/stringwithquotes/PrintQuotesAroundAStringUnitTest.java

@@ -0,0 +1,60 @@
+package com.baeldung.stringwithquotes;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class PrintQuotesAroundAStringUnitTest {
+    private final ByteArrayOutputStream outContent = new ByteArrayOutputStream();
+    private final PrintStream originalOut = System.out;
+
+    @BeforeEach
+    void replaceOut() {
+        System.setOut(new PrintStream(outContent));
+    }
+
+    @AfterEach
+    void restoreOut() {
+        System.setOut(originalOut);
+    }
+
+    @Test
+    void whenWrappingAStringWithEscapedQuote_thenGetExpectedResult() {
+        String theySay = "All Java programmers are cute!";
+        String quoted = "\"" + theySay + "\"";
+
+        System.out.println(quoted);
+
+        //assertion
+        String expected = "\"All Java programmers are cute!\"\n";
+        assertEquals(expected, outContent.toString());
+    }
+
+    @Test
+    void whenCallingReplaceAll_thenGetExpectedResult() {
+        String theySay = "Can you write Java code?";
+        String quoted = theySay.replaceAll("^|$", "\"");
+
+        System.out.println(quoted);
+
+        //assertion
+        String expected = "\"Can you write Java code?\"\n";
+        assertEquals(expected, outContent.toString());
+    }
+
+    @Test
+    void whenWrappingAStringWithQuoteChar_thenGetExpectedResult() {
+        String weSay = "Yes, we can write beautiful Java codes!";
+        String quoted = '"' + weSay + '"';
+        System.out.println(quoted);
+
+        //assertion
+        String expected = "\"Yes, we can write beautiful Java codes!\"\n";
+        assertEquals(expected, outContent.toString());
+    }
+}