Merge branch 'master' into master

2019-11-02 23:34:32 +02:00
parent 33998bdac8 6ec3e1c08f
commit 26e6d89a48
141 changed files with 995 additions and 687 deletions
@@ -0,0 +1,19 @@
+package com.baeldung.random;
+
+import java.util.Date;
+import java.util.concurrent.ThreadLocalRandom;
+
+public class LegacyRandomDateTimes {
+
+    public static Date between(Date startInclusive, Date endExclusive) {
+        long startMillis = startInclusive.getTime();
+        long endMillis = endExclusive.getTime();
+        long randomMillisSinceEpoch = ThreadLocalRandom.current().nextLong(startMillis, endMillis);
+
+        return new Date(randomMillisSinceEpoch);
+    }
+
+    public static Date timestamp() {
+        return new Date(ThreadLocalRandom.current().nextInt() * 1000L);
+    }
+}
@@ -0,0 +1,27 @@
+package com.baeldung.random;
+
+import java.time.Instant;
+import java.util.concurrent.ThreadLocalRandom;
+
+public class RandomDateTimes {
+
+    public static Instant timestamp() {
+        return Instant.ofEpochSecond(ThreadLocalRandom.current().nextInt());
+    }
+
+    public static Instant between(Instant startInclusive, Instant endExclusive) {
+        long startSeconds = startInclusive.getEpochSecond();
+        long endSeconds = endExclusive.getEpochSecond();
+        long random = ThreadLocalRandom.current().nextLong(startSeconds, endSeconds);
+
+        return Instant.ofEpochSecond(random);
+    }
+
+    public static Instant after(Instant startInclusive) {
+        return between(startInclusive, Instant.MAX);
+    }
+
+    public static Instant before(Instant upperExclusive) {
+        return between(Instant.MIN, upperExclusive);
+    }
+}
@@ -0,0 +1,20 @@
+package com.baeldung.random;
+
+import java.time.LocalDate;
+import java.util.concurrent.ThreadLocalRandom;
+
+public class RandomDates {
+
+    public static LocalDate between(LocalDate startInclusive, LocalDate endExclusive) {
+        long startEpochDay = startInclusive.toEpochDay();
+        long endEpochDay = endExclusive.toEpochDay();
+        long randomDay = ThreadLocalRandom.current().nextLong(startEpochDay, endEpochDay);
+
+        return LocalDate.ofEpochDay(randomDay);
+    }
+
+    public static LocalDate date() {
+        int hundredYears = 100 * 365;
+        return LocalDate.ofEpochDay(ThreadLocalRandom.current().nextInt(-hundredYears, hundredYears));
+    }
+}
@@ -0,0 +1,19 @@
+package com.baeldung.random;
+
+import java.time.LocalTime;
+import java.util.concurrent.ThreadLocalRandom;
+
+public class RandomTimes {
+
+    public static LocalTime between(LocalTime startTime, LocalTime endTime) {
+        int startSeconds = startTime.toSecondOfDay();
+        int endSeconds = endTime.toSecondOfDay();
+        int randomTime = ThreadLocalRandom.current().nextInt(startSeconds, endSeconds);
+
+        return LocalTime.ofSecondOfDay(randomTime);
+    }
+
+    public static LocalTime time() {
+        return between(LocalTime.MIN, LocalTime.MAX);
+    }
+}
@@ -0,0 +1,36 @@
+package com.baeldung.random;
+
+import org.junit.jupiter.api.RepeatedTest;
+
+import java.util.Date;
+import java.util.concurrent.TimeUnit;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class LegacyRandomDateTimesUnitTest {
+
+    private static final Date MIN_DATE = new Date(Long.MIN_VALUE);
+    private static final Date MAX_DATE = new Date(Long.MAX_VALUE);
+
+    @RepeatedTest(100)
+    void givenARange_WhenGenTimestamp_ShouldBeInRange() {
+        long aDay = TimeUnit.DAYS.toMillis(1);
+        long now = new Date().getTime();
+
+        Date hundredYearsAgo = new Date(now - aDay * 365 * 100);
+        Date tenDaysAgo = new Date(now - aDay * 10);
+
+        Date random = LegacyRandomDateTimes.between(hundredYearsAgo, tenDaysAgo);
+        assertThat(random).isBetween(hundredYearsAgo, tenDaysAgo);
+    }
+
+    @RepeatedTest(100)
+    void givenNoRange_WhenGenTimestamp_ShouldGenerateRandomTimestamps() {
+        Date random = LegacyRandomDateTimes.timestamp();
+
+        assertThat(random)
+                .isNotNull()
+                .isBetween(MIN_DATE, MAX_DATE);
+    }
+
+}
@@ -0,0 +1,27 @@
+package com.baeldung.random;
+
+import org.junit.jupiter.api.RepeatedTest;
+
+import java.time.Duration;
+import java.time.Instant;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class RandomDateTimesUnitTest {
+
+    @RepeatedTest(100)
+    void givenNoRange_WhenGenTimestamp_ShouldGenerateRandomTimestamps() {
+        Instant random = RandomDateTimes.timestamp();
+
+        assertThat(random).isBetween(Instant.MIN, Instant.MAX);
+    }
+
+    @RepeatedTest(100)
+    void givenARange_WhenGenTimestamp_ShouldBeInRange() {
+        Instant hundredYearsAgo = Instant.now().minus(Duration.ofDays(100 * 365));
+        Instant tenDaysAgo = Instant.now().minus(Duration.ofDays(10));
+
+        Instant random = RandomDateTimes.between(hundredYearsAgo, tenDaysAgo);
+        assertThat(random).isBetween(hundredYearsAgo, tenDaysAgo);
+    }
+}
@@ -0,0 +1,27 @@
+package com.baeldung.random;
+
+import org.junit.jupiter.api.RepeatedTest;
+
+import java.time.LocalDate;
+import java.time.Month;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class RandomDatesUnitTest {
+
+    @RepeatedTest(100)
+    void givenNoRange_WhenGenDate_ShouldGenerateRandomDates() {
+        LocalDate randomDay = RandomDates.date();
+
+        assertThat(randomDay).isAfter(LocalDate.MIN).isBefore(LocalDate.MAX);
+    }
+
+    @RepeatedTest(100)
+    void givenARange_WhenGenDate_ShouldBeInRange() {
+        LocalDate start = LocalDate.of(1989, Month.OCTOBER, 14);
+        LocalDate end = LocalDate.now();
+
+        LocalDate random = RandomDates.between(start, end);
+        assertThat(random).isAfter(start).isBefore(end);
+    }
+}
@@ -0,0 +1,20 @@
+package com.baeldung.random;
+
+import org.junit.jupiter.api.RepeatedTest;
+
+import java.time.LocalTime;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class RandomTimesUnitTest {
+
+    @RepeatedTest(100)
+    void givenARange_WhenGenTime_ShouldBeInRange() {
+        LocalTime morning = LocalTime.of(8, 30);
+        LocalTime randomTime = RandomTimes.between(LocalTime.MIDNIGHT, morning);
+
+        assertThat(randomTime)
+                .isAfter(LocalTime.MIDNIGHT).isBefore(morning)
+                .isAfter(LocalTime.MIN).isBefore(LocalTime.MAX);
+    }
+}
@@ -0,0 +1,16 @@
+package com.baeldung.trywithresource;
+
+public class AutoCloseableMain {
+
+    public static void main(String[] args) throws Exception {
+        orderOfClosingResources();
+    }
+
+    private static void orderOfClosingResources() throws Exception {
+        try (AutoCloseableResourcesFirst af = new AutoCloseableResourcesFirst();
+             AutoCloseableResourcesSecond as = new AutoCloseableResourcesSecond()) {
+            af.doSomething();
+            as.doSomething();
+        }
+    }
+}
@@ -0,0 +1,17 @@
+package com.baeldung.trywithresource;
+
+public class AutoCloseableResourcesFirst implements AutoCloseable {
+
+    public AutoCloseableResourcesFirst() {
+        System.out.println("Constructor -> AutoCloseableResources_First");
+    }
+
+    public void doSomething() {
+        System.out.println("Something -> AutoCloseableResources_First");
+    }
+
+    @Override
+    public void close() throws Exception {
+        System.out.println("Closed AutoCloseableResources_First");
+    }
+}
@@ -0,0 +1,17 @@
+package com.baeldung.trywithresource;
+
+public class AutoCloseableResourcesSecond implements AutoCloseable {
+
+    public AutoCloseableResourcesSecond() {
+        System.out.println("Constructor -> AutoCloseableResources_Second");
+    }
+
+    public void doSomething() {
+        System.out.println("Something -> AutoCloseableResources_Second");
+    }
+
+    @Override
+    public void close() throws Exception {
+        System.out.println("Closed AutoCloseableResources_Second");
+    }
+}
@@ -0,0 +1,8 @@
+package com.baeldung.trywithresource;
+
+public class MyResource implements AutoCloseable {
+    @Override
+    public void close() throws Exception {
+        System.out.println("Closed MyResource");
+    }
+}
@@ -0,0 +1,44 @@
+package com.baeldung.scanner;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.NoSuchElementException;
+import java.util.Scanner;
+
+import org.junit.Test;
+
+public class JavaScannerUnitTest {
+
+    @Test
+    public void whenReadingLines_thenCorrect() {
+        String input = "Scanner\nTest\n";
+        try (Scanner scanner = new Scanner(input)) {
+            assertEquals("Scanner", scanner.nextLine());
+            assertEquals("Test", scanner.nextLine());
+        }
+    }
+
+    @Test
+    public void whenReadingPartialLines_thenCorrect() {
+        String input = "Scanner\n";
+        try (Scanner scanner = new Scanner(input)) {
+            scanner.useDelimiter("");
+            scanner.next();
+            assertEquals("canner", scanner.nextLine());
+        }
+    }
+
+    @Test(expected = NoSuchElementException.class)
+    public void givenNoNewLine_whenReadingNextLine_thenThrowNoSuchElementException() {
+        try (Scanner scanner = new Scanner("")) {
+            String result = scanner.nextLine();
+        }
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void givenScannerIsClosed_whenReadingNextLine_thenThrowIllegalStateException() {
+        Scanner scanner = new Scanner("");
+        scanner.close();
+        String result = scanner.nextLine();
+    }
+}
@@ -0,0 +1,11 @@
+## Java String Operations
+
+This module contains articles about string operations.
+
+### Relevant Articles:
+- [Concatenating Strings In Java](https://www.baeldung.com/java-strings-concatenation)
+- [Checking for Empty or Blank Strings in Java](https://www.baeldung.com/java-blank-empty-strings)
+- [String Initialization in Java](https://www.baeldung.com/java-string-initialization)
+- [String toLowerCase and toUpperCase Methods in Java](https://www.baeldung.com/java-string-convert-case)
+- [Java String equalsIgnoreCase()](https://www.baeldung.com/java-string-equalsignorecase)
+- More articles: [[<-- prev]](../core-java-string-operations)
@@ -0,0 +1,81 @@
+<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-string-operations-2</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+    <name>core-java-string-operations-2</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>javax.validation</groupId>
+            <artifactId>validation-api</artifactId>
+            <version>${validation-api.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.hibernate.validator</groupId>
+            <artifactId>hibernate-validator</artifactId>
+            <version>${hibernate-validator.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>javax.el</groupId>
+            <artifactId>javax.el-api</artifactId>
+            <version>${javax.el-api.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.glassfish.web</groupId>
+            <artifactId>javax.el</artifactId>
+            <version>${javax.el.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>hamcrest-library</artifactId>
+            <version>${org.hamcrest.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-string-operations-2</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+    <properties>
+        <assertj.version>3.6.1</assertj.version>
+        <validation-api.version>2.0.0.Final</validation-api.version>
+        <commons-lang3.version>3.8.1</commons-lang3.version>
+        <guava.version>27.0.1-jre</guava.version>
+        <hibernate-validator.version>6.0.2.Final</hibernate-validator.version>
+        <javax.el-api.version>3.0.0</javax.el-api.version>
+        <javax.el.version>2.2.6</javax.el.version>
+    </properties>
+
+</project>
@@ -0,0 +1,8 @@
+package com.baeldung.emptystrings;
+
+class EmptyStringCheck {
+
+    boolean isEmptyString(String string) {
+        return string == null || string.isEmpty();
+    }
+}
@@ -0,0 +1,8 @@
+package com.baeldung.emptystrings;
+
+class Java5EmptyStringCheck {
+
+    boolean isEmptyString(String string) {
+        return string == null || string.length() == 0;
+    }
+}
@@ -0,0 +1,8 @@
+package com.baeldung.emptystrings;
+
+class PlainJavaBlankStringCheck {
+
+    boolean isBlankString(String string) {
+        return string == null || string.trim().isEmpty();
+    }
+}
@@ -0,0 +1,14 @@
+package com.baeldung.emptystrings;
+
+import javax.validation.constraints.Pattern;
+
+class SomeClassWithValidations {
+
+    @Pattern(regexp = "\\A(?!\\s*\\Z).+")
+    private String someString;
+
+    SomeClassWithValidations setSomeString(String someString) {
+        this.someString = someString;
+        return this;
+    }
+}
@@ -0,0 +1,29 @@
+package com.baeldung.changecase;
+
+import org.junit.Test;
+
+import java.util.Locale;
+
+import static org.junit.Assert.assertEquals;
+
+public class ToLowerCaseUnitTest {
+
+    private static final Locale TURKISH = new Locale("tr");
+    private String name = "John Doe";
+    private String foreignUppercase = "\u0049";
+
+    @Test
+    public void givenMixedCaseString_WhenToLowerCase_ThenResultIsLowerCase() {
+        assertEquals("john doe", name.toLowerCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToLowerCaseWithoutLocale_ThenResultIsLowerCase() {
+        assertEquals("\u0069", foreignUppercase.toLowerCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToLowerCaseWithLocale_ThenResultIsLowerCase() {
+        assertEquals("\u0131", foreignUppercase.toLowerCase(TURKISH));
+    }
+}
@@ -0,0 +1,29 @@
+package com.baeldung.changecase;
+
+import org.junit.Test;
+
+import java.util.Locale;
+
+import static org.junit.Assert.assertEquals;
+
+public class ToUpperCaseUnitTest {
+
+    private static final Locale TURKISH = new Locale("tr");
+    private String name = "John Doe";
+    private String foreignLowercase = "\u0069";
+
+    @Test
+    public void givenMixedCaseString_WhenToUpperCase_ThenResultIsUpperCase() {
+        assertEquals("JOHN DOE", name.toUpperCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToUpperCaseWithoutLocale_ThenResultIsUpperCase() {
+        assertEquals("\u0049", foreignLowercase.toUpperCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToUpperCaseWithLocale_ThenResultIsUpperCase() {
+        assertEquals("\u0130", foreignLowercase.toUpperCase(TURKISH));
+    }
+}
@@ -0,0 +1,138 @@
+package com.baeldung.emptystrings;
+
+import com.google.common.base.Strings;
+import org.apache.commons.lang3.StringUtils;
+import org.junit.Test;
+
+import javax.validation.ConstraintViolation;
+import javax.validation.Validation;
+import javax.validation.Validator;
+import javax.validation.ValidatorFactory;
+import java.util.Set;
+
+import static org.hamcrest.Matchers.iterableWithSize;
+import static org.junit.Assert.*;
+
+public class EmptyStringsUnitTest {
+
+    private String emptyString = "";
+    private String blankString = "  \n\t  ";
+    private String nonEmptyString = "   someString   ";
+
+    /*
+     * EmptyStringCheck
+     */
+    @Test
+    public void givenSomeEmptyString_thenEmptyStringCheckIsEmptyStringReturnsTrue() {
+        assertTrue(new EmptyStringCheck().isEmptyString(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenEmptyStringCheckIsEmptyStringReturnsFalse() {
+        assertFalse(new EmptyStringCheck().isEmptyString(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenEmptyStringCheckIsEmptyStringReturnsFalse() {
+        assertFalse(new EmptyStringCheck().isEmptyString(blankString));
+    }
+
+    /*
+     * Java5EmptyStringCheck
+     */
+    @Test
+    public void givenSomeEmptyString_thenJava5EmptyStringCheckIsEmptyStringReturnsTrue() {
+        assertTrue(new Java5EmptyStringCheck().isEmptyString(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenJava5EmptyStringCheckIsEmptyStringReturnsFalse() {
+        assertFalse(new Java5EmptyStringCheck().isEmptyString(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenJava5EmptyStringCheckIsEmptyStringReturnsFalse() {
+        assertFalse(new Java5EmptyStringCheck().isEmptyString(blankString));
+    }
+
+    /*
+     * PlainJavaBlankStringCheck
+     */
+    @Test
+    public void givenSomeEmptyString_thenPlainJavaBlankStringCheckIsBlankStringReturnsTrue() {
+        assertTrue(new PlainJavaBlankStringCheck().isBlankString(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenPlainJavaBlankStringCheckIsBlankStringReturnsFalse() {
+        assertFalse(new PlainJavaBlankStringCheck().isBlankString(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenPlainJavaBlankStringCheckIsBlankStringReturnsTrue() {
+        assertTrue(new PlainJavaBlankStringCheck().isBlankString(blankString));
+    }
+
+    /*
+     * Apache Commons Lang StringUtils
+     */
+    @Test
+    public void givenSomeEmptyString_thenStringUtilsIsBlankReturnsTrue() {
+        assertTrue(StringUtils.isBlank(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenStringUtilsIsBlankReturnsFalse() {
+        assertFalse(StringUtils.isBlank(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenStringUtilsIsBlankReturnsTrue() {
+        assertTrue(StringUtils.isBlank(blankString));
+    }
+
+    /*
+     * Google Guava Strings
+     */
+    @Test
+    public void givenSomeEmptyString_thenStringsIsNullOrEmptyStringReturnsTrue() {
+        assertTrue(Strings.isNullOrEmpty(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenStringsIsNullOrEmptyStringReturnsFalse() {
+        assertFalse(Strings.isNullOrEmpty(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenStringsIsNullOrEmptyStringReturnsFalse() {
+        assertFalse(Strings.isNullOrEmpty(blankString));
+    }
+
+    /*
+     * Bean Validation
+     */
+    private ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
+    private Validator validator = factory.getValidator();
+
+    @Test
+    public void givenSomeEmptyString_thenBeanValidationReturnsViolations() {
+        SomeClassWithValidations someClassWithValidations = new SomeClassWithValidations().setSomeString(emptyString);
+        Set<ConstraintViolation<SomeClassWithValidations>> violations = validator.validate(someClassWithValidations);
+        assertThat(violations, iterableWithSize(1));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenBeanValidationValidatesWithoutViolations() {
+        SomeClassWithValidations someClassWithValidations = new SomeClassWithValidations().setSomeString(nonEmptyString);
+        Set<ConstraintViolation<SomeClassWithValidations>> violations = validator.validate(someClassWithValidations);
+        assertThat(violations, iterableWithSize(0));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenBeanValidationReturnsViolations() {
+        SomeClassWithValidations someClassWithValidations = new SomeClassWithValidations().setSomeString(blankString);
+        Set<ConstraintViolation<SomeClassWithValidations>> violations = validator.validate(someClassWithValidations);
+        assertThat(violations, iterableWithSize(1));
+    }
+}
@@ -0,0 +1,26 @@
+package com.baeldung.equalsIgnoreCase;
+
+import org.apache.commons.lang3.StringUtils;
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class StringEqualsIgnoreCaseUnitTest {
+    private String string1 = "equals ignore case";
+    private String string2 = "EQUALS IGNORE CASE";
+
+    @Test
+    public void givenEqualStringsWithDifferentCase_whenUsingEqualsIgnoreCase_ThenTheyAreEqual() {
+        assertThat(string1.equalsIgnoreCase(string2)).isTrue();
+    }
+
+    @Test
+    public void givenEqualStringsWithDifferentCase_whenUsingApacheCommonsEqualsIgnoreCase_ThenTheyAreEqual() {
+        assertThat(StringUtils.equalsIgnoreCase(string1, string2)).isTrue();
+    }
+
+    @Test
+    public void givenAStringAndNullValue_whenUsingApacheCommonsEqualsIgnoreCase_ThenTheyAreNotEqual() {
+        assertThat(StringUtils.equalsIgnoreCase(string1, null)).isFalse();
+    }
+}
@@ -0,0 +1,56 @@
+package com.baeldung.initialization;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class StringInitializationUnitTest {
+
+    private String fieldString;
+
+    void printDeclaredOnlyString() {
+        String localVarString = null;
+
+        System.out.println(localVarString); // compilation error
+        System.out.println(fieldString);
+    }
+
+    @Test
+    public void givenDeclaredFeldStringAndNullString_thenCompareEquals() {
+        String localVarString = null;
+
+        assertEquals(fieldString, localVarString);
+    }
+
+    @Test
+    public void givenTwoStringsWithSameLiteral_thenCompareReferencesEquals() {
+        String literalOne = "Baeldung";
+        String literalTwo = "Baeldung";
+
+        assertTrue(literalOne == literalTwo);
+    }
+
+    @Test
+    public void givenTwoStringsUsingNew_thenCompareReferencesNotEquals() {
+        String newStringOne = new String("Baeldung");
+        String newStringTwo = new String("Baeldung");
+
+        assertFalse(newStringOne == newStringTwo);
+    }
+
+    @Test
+    public void givenEmptyLiteralStringsAndNewObject_thenCompareEquals() {
+        String emptyLiteral = "";
+        String emptyNewString = new String("");
+
+        assertEquals(emptyLiteral, emptyNewString);
+    }
+
+    @Test
+    public void givenEmptyStringObjects_thenCompareEquals() {
+        String emptyNewString = new String("");
+        String emptyNewStringTwo = new String();
+
+        assertEquals(emptyNewString, emptyNewStringTwo);
+    }
+}
@@ -0,0 +1,105 @@
+package com.baeldung.stringconcatenation;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.StringJoiner;
+import java.util.stream.Collectors;
+
+import static org.junit.Assert.assertEquals;
+
+public class StringConcatenationUnitTest {
+
+  @Test
+  public void givenMultipleStrings_whenConcatUsingStringBuilder_checkStringCorrect() {
+
+    StringBuilder stringBuilder = new StringBuilder(100);
+    stringBuilder.append("Baeldung");
+    stringBuilder.append(" is");
+    stringBuilder.append(" awesome");
+
+    assertEquals("Baeldung is awesome", stringBuilder.toString());
+
+  }
+
+  @Test
+  public void givenMultipleString_whenConcatUsingAdditionOperator_checkStringCorrect() {
+
+    String myString = "The " + "quick " + "brown " + "fox...";
+
+    assertEquals("The quick brown fox...", myString);
+  }
+
+
+  @Test
+  public void givenMultipleStrings_whenConcatUsingStringFormat_checkStringCorrect() {
+
+    String myString = String.format("%s %s %.2f %s %s, %s...", "I",
+            "ate",
+            2.5056302,
+            "blueberry",
+            "pies",
+            "oops");
+
+
+    assertEquals("I ate 2.51 blueberry pies, oops...", myString);
+  }
+
+  @Test
+  public void givenMultipleStrings_whenStringConcatUsed_checkStringCorrect() {
+
+    String myString = "Both".concat(" fickle")
+            .concat(" dwarves")
+            .concat(" jinx")
+            .concat(" my")
+            .concat(" pig")
+            .concat(" quiz");
+
+    assertEquals("Both fickle dwarves jinx my pig quiz", myString);
+
+
+  }
+
+  @Test
+  public void givenMultipleStrings_whenStringJoinUsed_checkStringCorrect() {
+
+    String[] strings = {"I'm", "running", "out", "of", "pangrams!"};
+
+    String myString = String.join(" ", strings);
+
+    assertEquals("I'm running out of pangrams!", myString);
+
+  }
+
+  @Test
+  public void givenMultipleStrings_whenStringJoinerUsed_checkStringCorrect() {
+
+    StringJoiner fruitJoiner = new StringJoiner(", ");
+    fruitJoiner.add("Apples");
+    fruitJoiner.add("Oranges");
+    fruitJoiner.add("Bananas");
+
+    assertEquals("Apples, Oranges, Bananas", fruitJoiner.toString());
+  }
+
+  @Test
+  public void givenMultipleStrings_whenArrayJoiner_checkStringCorrect() {
+
+    String[] myFavouriteLanguages = {"Java", "JavaScript", "Python"};
+
+    String toString = Arrays.toString(myFavouriteLanguages);
+
+    assertEquals("[Java, JavaScript, Python]", toString);
+  }
+
+  @Test
+  public void givenArrayListOfStrings_whenCollectorsJoin_checkStringCorrect() {
+
+    List<String> awesomeAnimals = Arrays.asList("Shark", "Panda", "Armadillo");
+
+    String animalString = awesomeAnimals.stream().collect(Collectors.joining(", "));
+
+    assertEquals("Shark, Panda, Armadillo", animalString);
+  }
+}
@@ -0,0 +1,16 @@
+## Java String Operations
+
+This module contains articles about string operations.
+
+### Relevant Articles:
+- [Comparing Strings in Java](https://www.baeldung.com/java-compare-strings)
+- [Check If a String Is Numeric in Java](https://www.baeldung.com/java-check-string-number)
+- [Get Substring from String in Java](https://www.baeldung.com/java-substring)
+- [Split a String in Java](https://www.baeldung.com/java-split-string)
+- [Common String Operations in Java](https://www.baeldung.com/java-string-operations)
+- [Java toString() Method](https://www.baeldung.com/java-tostring)
+- [String Operations with Java Streams](https://www.baeldung.com/java-stream-operations-on-strings)
+- [Adding a Newline Character to a String in Java](https://www.baeldung.com/java-string-newline)
+- [Check If a String Contains a Substring](https://www.baeldung.com/java-string-contains-substring)
+- [Java Base64 Encoding and Decoding](https://www.baeldung.com/java-base64-encode-and-decode)
+- More articles: [[next -->]](../core-java-string-operations-2)
@@ -0,0 +1,66 @@
+<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-string-operations</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+    <name>core-java-string-operations</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+            <version>${jmh-core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>log4j</groupId>
+            <artifactId>log4j</artifactId>
+            <version>${log4j.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+            <version>${jmh-generator.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>commons-codec</groupId>
+            <artifactId>commons-codec</artifactId>
+            <version>${commons-codec.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-string-operations</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+    <properties>
+        <commons-lang3.version>3.8.1</commons-lang3.version>
+        <assertj.version>3.6.1</assertj.version>
+        <commons-codec.version>1.10</commons-codec.version>
+    </properties>
+
+</project>
@@ -0,0 +1,73 @@
+package com.baeldung.isnumeric;
+
+import java.util.concurrent.TimeUnit;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.runner.Runner;
+import org.openjdk.jmh.runner.RunnerException;
+import org.openjdk.jmh.runner.options.Options;
+import org.openjdk.jmh.runner.options.OptionsBuilder;
+
+public class Benchmarking {
+    public static void main(String[] args) throws RunnerException {
+        Options opt = new OptionsBuilder().include(Benchmarking.class.getSimpleName())
+            .forks(1)
+            .build();
+
+        new Runner(opt).run();
+    }
+
+    @State(Scope.Thread)
+    public static class ExecutionPlan {
+        public String number = Integer.toString(Integer.MAX_VALUE);
+        public boolean isNumber = false;
+        public IsNumeric isNumeric = new IsNumeric();
+    }
+
+    @Benchmark
+    @BenchmarkMode(Mode.AverageTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    public void usingCoreJava(ExecutionPlan plan) {
+        plan.isNumber = plan.isNumeric.usingCoreJava(plan.number);
+    }
+
+    @Benchmark
+    @BenchmarkMode(Mode.AverageTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    public void usingRegularExpressions(ExecutionPlan plan) {
+        plan.isNumber = plan.isNumeric.usingRegularExpressions(plan.number);
+    }
+
+    @Benchmark
+    @BenchmarkMode(Mode.AverageTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    public void usingNumberUtils_isCreatable(ExecutionPlan plan) {
+        plan.isNumber = plan.isNumeric.usingNumberUtils_isCreatable(plan.number);
+    }
+
+    @Benchmark
+    @BenchmarkMode(Mode.AverageTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    public void usingNumberUtils_isParsable(ExecutionPlan plan) {
+        plan.isNumber = plan.isNumeric.usingNumberUtils_isParsable(plan.number);
+    }
+
+    @Benchmark
+    @BenchmarkMode(Mode.AverageTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    public void usingStringUtils_isNumeric(ExecutionPlan plan) {
+        plan.isNumber = plan.isNumeric.usingStringUtils_isNumeric(plan.number);
+    }
+
+    @Benchmark
+    @BenchmarkMode(Mode.AverageTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    public void usingStringUtils_isNumericSpace(ExecutionPlan plan) {
+        plan.isNumber = plan.isNumeric.usingStringUtils_isNumericSpace(plan.number);
+    }
+}
@@ -0,0 +1,18 @@
+package com.baeldung.isnumeric;
+
+import java.util.Scanner;
+
+public class CheckIntegerInput {
+
+    public static void main(String[] args) {
+        try (Scanner scanner = new Scanner(System.in)) {
+            System.out.println("Enter an integer : ");
+
+            if (scanner.hasNextInt()) {
+                System.out.println("You entered : " + scanner.nextInt());
+            } else {
+                System.out.println("The input is not an integer");
+            }
+        }
+    }
+}
@@ -0,0 +1,35 @@
+package com.baeldung.isnumeric;
+
+import org.apache.commons.lang3.StringUtils;
+import org.apache.commons.lang3.math.NumberUtils;
+
+public class IsNumeric {
+    public boolean usingCoreJava(String strNum) {
+        try {
+            Double.parseDouble(strNum);
+        } catch (NumberFormatException | NullPointerException nfe) {
+            return false;
+        }
+        return true;
+    }
+
+    public boolean usingRegularExpressions(String strNum) {
+        return strNum.matches("-?\\d+(\\.\\d+)?");
+    }
+
+    public boolean usingNumberUtils_isCreatable(String strNum) {
+        return NumberUtils.isCreatable(strNum);
+    }
+
+    public boolean usingNumberUtils_isParsable(String strNum) {
+        return NumberUtils.isParsable(strNum);
+    }
+
+    public boolean usingStringUtils_isNumeric(String strNum) {
+        return StringUtils.isNumeric(strNum);
+    }
+
+    public boolean usingStringUtils_isNumericSpace(String strNum) {
+        return StringUtils.isNumericSpace(strNum);
+    }
+}
--- a/Show More
+++ b/Show More