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java-strings/README.md

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+## Java Strings Cookbooks and Examples
+
+This module contains articles about strings in Java.
+
+### Relevant Articles:
+- [String Operations with Java Streams](https://www.baeldung.com/java-stream-operations-on-strings)
+- [Use char[] Array Over a String for Manipulating Passwords in Java?](https://www.baeldung.com/java-storing-passwords)
+- [Compact Strings in Java 9](https://www.baeldung.com/java-9-compact-string)
+- [Java Check a String for Lowercase/Uppercase Letter, Special Character and Digit](https://www.baeldung.com/java-lowercase-uppercase-special-character-digit-regex)
+- [String Not Empty Test Assertions in Java](https://www.baeldung.com/java-assert-string-not-empty)
+- [String Performance Hints](https://www.baeldung.com/java-string-performance)
+- [Using indexOf to Find All Occurrences of a Word in a String](https://www.baeldung.com/java-indexOf-find-string-occurrences)
+- [Adding a Newline Character to a String in Java](https://www.baeldung.com/java-string-newline)
+- [Remove or Replace Part of a String in Java](https://www.baeldung.com/java-remove-replace-string-part)
+- [Replace a Character at a Specific Index in a String in Java](https://www.baeldung.com/java-replace-character-at-index)
+- More articles: [[next -->]](/java-strings-2)

java-strings/pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.baeldung</groupId>
+    <artifactId>java-strings</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+    <name>java-strings</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>commons-io</groupId>
+            <artifactId>commons-io</artifactId>
+            <version>${commons-io.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>log4j</groupId>
+            <artifactId>log4j</artifactId>
+            <version>${log4j.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>commons-codec</groupId>
+            <artifactId>commons-codec</artifactId>
+            <version>${commons-codec.version}</version>
+        </dependency>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+            <version>${jmh-core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+            <version>${jmh-generator.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.ibm.icu</groupId>
+            <artifactId>icu4j</artifactId>
+            <version>${icu4j.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <version>${junit-jupiter-api.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>hamcrest-library</artifactId>
+            <version>${org.hamcrest.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+    </dependencies>
+
+    <build>
+        <finalName>java-strings</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <source>${java.version}</source>
+                    <target>${java.version}</target>
+                    <compilerArgument>-parameters</compilerArgument>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <!-- util -->
+        <commons-lang3.version>3.8.1</commons-lang3.version>
+        <commons-codec.version>1.10</commons-codec.version>
+        <!-- testing -->
+        <assertj.version>3.6.1</assertj.version>
+        <icu4j.version>61.1</icu4j.version>
+        <guava.version>27.0.1-jre</guava.version>
+		<junit-jupiter-api.version>5.3.1</junit-jupiter-api.version>
+		<commons-text.version>1.4</commons-text.version>
+    </properties>
+
+</project>

java-strings/src/main/java/com/baeldung/java9/compactstring/CompactStringDemo.java

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+package com.baeldung.java9.compactstring;
+
+import java.util.List;
+import static java.util.stream.Collectors.toList;
+import java.util.stream.IntStream;
+
+public class CompactStringDemo {
+
+    public static void main(String[] args) {
+        long startTime = System.currentTimeMillis();
+        List strings = IntStream.rangeClosed(1, 10_000_000)
+          .mapToObj(Integer::toString).collect(toList());
+        long totalTime = System.currentTimeMillis() - startTime;
+        System.out.println("Generated " + strings.size() + " strings in " 
+          + totalTime + " ms.");
+
+        startTime = System.currentTimeMillis();
+        String appended = (String) strings.stream().limit(100_000)
+          .reduce("", (left, right) -> left.toString() + right.toString());
+        totalTime = System.currentTimeMillis() - startTime;
+        System.out.println("Created string of length " + appended.length() 
+          + " in " + totalTime + " ms.");
+    }
+}

java-strings/src/main/java/com/baeldung/string/JoinerSplitter.java

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+package com.baeldung.string;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class JoinerSplitter {
+
+	public static String join ( String[] arrayOfString ) {
+		return Arrays.asList(arrayOfString)
+				.stream()
+				.map(x -> x)
+				.collect(Collectors.joining(","));
+	}
+	
+	public static String joinWithPrefixPostFix ( String[] arrayOfString ) {
+		return Arrays.asList(arrayOfString)
+				.stream()
+				.map(x -> x)
+				.collect(Collectors.joining(",","[","]"));
+	}
+	
+	public static List<String> split ( String str ) {
+		return Stream.of(str.split(","))
+				.map (elem -> new String(elem))
+				.collect(Collectors.toList());
+	}
+	
+	public static List<Character> splitToListOfChar ( String str ) {
+		return str.chars()
+				.mapToObj(item -> (char) item)
+				.collect(Collectors.toList());
+	}
+	
+	public static Map<String, String> arrayToMap(String[] arrayOfString) {
+		return Arrays.asList(arrayOfString)
+				.stream()
+				.map(str -> str.split(":"))
+				.collect(Collectors.<String[], String, String>toMap(str -> str[0], str -> str[1]));
+	}
+		
+}

java-strings/src/main/java/com/baeldung/string/ReplaceCharacterInString.java

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+package com.baeldung.string;
+
+public class ReplaceCharacterInString {
+
+    public String replaceCharSubstring(String str, char ch, int index) {
+        String myString = str.substring(0, index) + ch + str.substring(index + 1);
+        return myString;
+    }
+
+    public String replaceCharUsingCharArray(String str, char ch, int index) {
+        char[] chars = str.toCharArray();
+        chars[index] = ch;
+        return String.valueOf(chars);
+    }
+
+
+    public String replaceCharStringBuilder(String str, char ch, int index) {
+        StringBuilder myString = new StringBuilder(str);
+        myString.setCharAt(index, ch);
+        return myString.toString();
+    }
+
+    public String replaceCharStringBuffer(String str, char ch, int index) {
+        StringBuffer myString = new StringBuffer(str);
+        myString.setCharAt(index, ch);
+        return myString.toString();
+    }
+
+}

java-strings/src/main/java/com/baeldung/string/StringPerformance.java

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+package com.baeldung.string;
+
+import com.google.common.base.Splitter;
+import org.apache.commons.lang3.StringUtils;
+import org.openjdk.jmh.annotations.*;
+import org.openjdk.jmh.runner.Runner;
+import org.openjdk.jmh.runner.options.Options;
+import org.openjdk.jmh.runner.options.OptionsBuilder;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.StringTokenizer;
+import java.util.concurrent.TimeUnit;
+import java.util.regex.Pattern;
+
+@BenchmarkMode(Mode.SingleShotTime)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+@Measurement(batchSize = 100000, iterations = 10)
+@Warmup(batchSize = 100000, iterations = 10)
+@State(Scope.Thread)
+public class StringPerformance {
+
+    protected String baeldung = "baeldung";
+    protected String longString = "Hello baeldung, I am a bit longer than other Strings";
+    protected String formatString = "hello %s, nice to meet you";
+    protected String formatDigit = "%d";
+    protected String emptyString = " ";
+    protected String result = "";
+
+    protected int sampleNumber = 100;
+
+    protected Pattern spacePattern = Pattern.compile(emptyString);
+    protected Pattern longPattern = Pattern.compile(longString);
+    protected List<String> stringSplit = new ArrayList<>();
+    protected List<String> stringTokenizer = new ArrayList<>();
+
+    @Benchmark
+    public String benchmarkStringDynamicConcat() {
+        result += baeldung;
+        return result;
+    }
+
+    @Benchmark
+    public StringBuilder  benchmarkStringBuilder() {
+        StringBuilder stringBuilder = new StringBuilder(result);
+        stringBuilder.append(baeldung);
+        return stringBuilder;
+    }
+
+    @Benchmark
+    public StringBuffer benchmarkStringBuffer() {
+        StringBuffer stringBuffer = new StringBuffer(result);
+        stringBuffer.append(baeldung);
+        return stringBuffer;
+    }
+
+    @Benchmark
+    public String benchmarkStringConstructor() {
+        String result = new String("baeldung");
+        return result;
+    }
+
+    @Benchmark
+    public String benchmarkStringLiteral() {
+        String result = "baeldung";
+        return result;
+    }
+
+    @Benchmark
+    public String benchmarkStringFormat_s() {
+        return String.format(formatString, baeldung);
+    }
+
+    @Benchmark
+    public String benchmarkStringConcat() {
+        result = result.concat(baeldung);
+        return result;
+    }
+
+    @Benchmark
+    public String benchmarkStringIntern() {
+        return baeldung.intern();
+    }
+
+    @Benchmark
+    public String benchmarkStringReplace() {
+        return longString.replace("average", " average !!!");
+    }
+
+    @Benchmark
+    public String benchmarkStringUtilsReplace() {
+        return StringUtils.replace(longString, "average", " average !!!");
+    }
+
+    @Benchmark
+    public List<String> benchmarkGuavaSplitter() {
+        return Splitter.on(" ").trimResults()
+                .omitEmptyStrings()
+                .splitToList(longString);
+    }
+
+    @Benchmark
+    public String [] benchmarkStringSplit() {
+        return longString.split(emptyString);
+    }
+
+    @Benchmark
+    public String [] benchmarkStringSplitPattern() {
+        return spacePattern.split(longString, 0);
+    }
+
+    @Benchmark
+    public List benchmarkStringTokenizer() {
+        StringTokenizer st = new StringTokenizer(longString);
+        while (st.hasMoreTokens()) {
+            stringTokenizer.add(st.nextToken());
+        }
+        return stringTokenizer;
+    }
+
+    @Benchmark
+    public List benchmarkStringIndexOf() {
+        int pos = 0, end;
+        while ((end = longString.indexOf(' ', pos)) >= 0) {
+            stringSplit.add(longString.substring(pos, end));
+            pos = end + 1;
+        }
+        return stringSplit;
+    }
+
+    @Benchmark
+    public String benchmarkIntegerToString() {
+        return Integer.toString(sampleNumber);
+    }
+
+    @Benchmark
+    public String benchmarkStringValueOf() {
+        return String.valueOf(sampleNumber);
+    }
+
+
+    @Benchmark
+    public String benchmarkStringConvertPlus() {
+        return sampleNumber + "";
+    }
+
+        @Benchmark
+    public String benchmarkStringFormat_d() {
+        return String.format(formatDigit, sampleNumber);
+    }
+
+    @Benchmark
+    public boolean benchmarkStringEquals() {
+        return longString.equals(baeldung);
+    }
+
+
+    @Benchmark
+    public boolean benchmarkStringEqualsIgnoreCase() {
+        return longString.equalsIgnoreCase(baeldung);
+    }
+
+    @Benchmark
+    public boolean benchmarkStringMatches() {
+        return longString.matches(baeldung);
+    }
+
+    @Benchmark
+    public boolean benchmarkPrecompiledMatches() {
+        return longPattern.matcher(baeldung).matches();
+    }
+
+    @Benchmark
+    public int benchmarkStringCompareTo() {
+        return longString.compareTo(baeldung);
+    }
+
+    @Benchmark
+    public boolean benchmarkStringIsEmpty() {
+        return longString.isEmpty();
+    }
+
+    @Benchmark
+    public boolean benchmarkStringLengthZero() {
+        return longString.length() == 0;
+    }
+
+    public static void main(String[] args) throws Exception {
+        Options options = new OptionsBuilder()
+                .include(StringPerformance.class.getSimpleName()).threads(1)
+                .forks(1).shouldFailOnError(true)
+                .shouldDoGC(true)
+                .jvmArgs("-server").build();
+        new Runner(options).run();
+    }
+}

java-strings/src/main/java/com/baeldung/string/newline/AddingNewLineToString.java

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+package com.baeldung.string.newline;
+
+public class AddingNewLineToString {
+	
+	public static void main(String[] args) {
+		String line1 = "Humpty Dumpty sat on a wall.";
+		String line2 = "Humpty Dumpty had a great fall.";
+		String rhyme = "";
+		
+		System.out.println("***New Line in a String in Java***");
+		//1. Using "\n"
+		System.out.println("1. Using \\n");
+		rhyme = line1 + "\n" + line2;
+		System.out.println(rhyme);
+		
+		//2. Using "\r\n"
+		System.out.println("2. Using \\r\\n");
+		rhyme = line1 + "\r\n" + line2;
+		System.out.println(rhyme);
+		
+		//3. Using "\r"
+		System.out.println("3. Using \\r");
+		rhyme = line1 + "\r" + line2;
+		System.out.println(rhyme);
+		
+		//4. Using "\n\r" Note that this is not same as "\r\n"
+		//   Using "\n\r" is equivalent to adding two lines
+		System.out.println("4. Using \\n\\r");
+		rhyme = line1 + "\n\r" + line2;
+		System.out.println(rhyme);
+		
+		//5. Using System.lineSeparator()
+		System.out.println("5. Using System.lineSeparator()");
+		rhyme = line1 + System.lineSeparator() + line2;
+		System.out.println(rhyme);
+		
+		//6. Using System.getProperty("line.separator")
+		System.out.println("6. Using System.getProperty(\"line.separator\")");
+		rhyme = line1 + System.getProperty("line.separator") + line2;
+		System.out.println(rhyme);
+		
+		System.out.println("***HTML to rendered in a browser***");
+		//1. Line break for HTML using <br>
+		System.out.println("1. Line break for HTML using <br>");
+		rhyme = line1 + "<br>" + line2;
+		System.out.println(rhyme);
+		
+		//2. Line break for HTML using “&#10;”
+		System.out.println("2. Line break for HTML using &#10;");
+		rhyme = line1 + "&#10;" + line2;
+		System.out.println(rhyme);
+		
+		//3. Line break for HTML using “&#13;”
+		System.out.println("3. Line break for HTML using &#13;");
+		rhyme = line1 + "&#13;" + line2;
+		System.out.println(rhyme);
+		
+		//4. Line break for HTML using “&#10&#13;;”
+		System.out.println("4. Line break for HTML using &#10;&#13;");
+		rhyme = line1 + "&#10;&#13;" + line2;
+		System.out.println(rhyme);
+		
+		//5. Line break for HTML using \n”
+		System.out.println("5. Line break for HTML using \\n");
+		rhyme = line1 + "\n" + line2;
+		System.out.println(rhyme);
+	}
+
+}

java-strings/src/main/java/com/baeldung/string/searching/WordIndexer.java

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+package com.baeldung.string.searching;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class WordIndexer {
+
+    public List<Integer> findWord(String textString, String word) {
+        int index = 0;
+        List<Integer> indexes = new ArrayList<Integer>();
+        String lowerCaseTextString = textString.toLowerCase();
+        String lowerCaseWord = word.toLowerCase();
+
+        while(index != -1) {
+            index = lowerCaseTextString.indexOf(lowerCaseWord, index);
+            if (index == -1) {
+                break;
+            }
+
+            indexes.add(index);
+            index++;
+        }
+        return indexes;
+    }
+
+
+
+    public List<Integer> findWordUpgrade(String textString, String word) {
+        int index = 0;
+        List<Integer> indexes = new ArrayList<Integer>();
+        StringBuilder output = new StringBuilder();
+        String lowerCaseTextString = textString.toLowerCase();
+        String lowerCaseWord = word.toLowerCase();
+        int wordLength = 0;
+
+        while(index != -1){
+            index = lowerCaseTextString.indexOf(lowerCaseWord, index + wordLength);  // Slight improvement
+            if (index != -1) {
+                indexes.add(index);
+            }
+            wordLength = word.length();
+        }
+        return indexes;
+    }
+}

java-strings/src/main/resources/data.csv

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+1|IND|India
+2|MY|Malaysia
+3|AU|Australia

java-strings/src/main/resources/logback.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

java-strings/src/test/java/com/baeldung/CharArrayToStringUnitTest.java

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+package com.baeldung;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+public class CharArrayToStringUnitTest {
+
+    @Test
+    public void givenCharArray_whenCallingStringConstructor_shouldConvertToString() {
+        char[] charArray = { 'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r' };
+        String result = new String(charArray);
+        String expectedValue = "character";
+
+        assertEquals(expectedValue, result);
+    }
+
+    @Test
+    public void givenCharArray_whenCallingStringConstructorWithOffsetAndLength_shouldConvertToString() {
+        char[] charArray = { 'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r' };
+        String result = new String(charArray, 4, 3);
+        String expectedValue = "act";
+
+        assertEquals(expectedValue, result);
+    }
+
+    @Test
+    public void givenCharArray_whenCallingStringCopyValueOf_shouldConvertToString() {
+        char[] charArray = { 'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r' };
+        String result = String.copyValueOf(charArray);
+        String expectedValue = "character";
+
+        assertEquals(expectedValue, result);
+    }
+
+    @Test
+    public void givenCharArray_whenCallingStringCopyValueOfWithOffsetAndLength_shouldConvertToString() {
+        char[] charArray = { 'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r' };
+        String result = String.copyValueOf(charArray, 0, 4);
+        String expectedValue = "char";
+
+        assertEquals(expectedValue, result);
+    }
+
+    @Test
+    public void givenCharArray_whenCallingStringValueOf_shouldConvertToString() {
+        char[] charArray = { 'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r' };
+        String result = String.valueOf(charArray);
+        String expectedValue = "character";
+
+        assertEquals(expectedValue, result);
+    }
+
+    @Test
+    public void givenCharArray_whenCallingStringValueOfWithOffsetAndLength_shouldConvertToString() {
+        char[] charArray = { 'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r' };
+        String result = String.valueOf(charArray, 3, 4);
+        String expectedValue = "ract";
+
+        assertEquals(expectedValue, result);
+    }
+}

java-strings/src/test/java/com/baeldung/StringToCharArrayUnitTest.java

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+package com.baeldung;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+public class StringToCharArrayUnitTest {
+
+    @Test
+    public void givenString_whenCallingStringToCharArray_shouldConvertToCharArray() {
+        String givenString = "characters";
+
+        char[] result = givenString.toCharArray();
+
+        char[] expectedCharArray = { 'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r', 's' };
+
+        assertArrayEquals(expectedCharArray, result);
+    }
+
+}

java-strings/src/test/java/com/baeldung/chararraypassword/PasswordStoreExamplesUnitTest.java

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+package com.baeldung.chararraypassword;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class PasswordStoreExamplesUnitTest {
+
+	String stringPassword = "password";
+	char[] charPassword = new char[]{'p', 'a', 's', 's', 'w', 'o', 'r', 'd'};
+
+	@Test
+	public void givenStringHashCode_WhenStringValueChanged_ThenHashCodesNotEqualAndValesNotEqual() {
+		String originalHashCode = Integer.toHexString(stringPassword.hashCode());
+
+		stringPassword = "********";
+		String changedHashCode = Integer.toHexString(stringPassword.hashCode());
+
+		assertThat(originalHashCode).isNotEqualTo(changedHashCode);
+		assertThat(stringPassword).isNotEqualTo("password");
+	}
+
+	@Test
+	public void givenStringHashCode_WhenStringValueChangedAndStringValueReassigned_ThenHashCodesEqualAndValesEqual() {
+		String originalHashCode = Integer.toHexString(stringPassword.hashCode());
+
+		stringPassword = "********";
+		stringPassword = "password";
+		String reassignedHashCode = Integer.toHexString(stringPassword.hashCode());
+
+		assertThat(originalHashCode).isEqualTo(reassignedHashCode);
+		assertThat(stringPassword).isEqualTo("password");
+	}
+
+	@Test
+	public void givenStringHashCode_WhenStringValueReplaced_ThenHashCodesEqualAndValesEqual() {
+		String originalHashCode = Integer.toHexString(stringPassword.hashCode());
+
+		String newString = "********";
+		stringPassword.replace(stringPassword, newString);
+
+		String hashCodeAfterReplace = Integer.toHexString(stringPassword.hashCode());
+
+		assertThat(originalHashCode).isEqualTo(hashCodeAfterReplace);
+		assertThat(stringPassword).isEqualTo("password");
+	}
+
+	@Test
+	public void givenCharArrayHashCode_WhenArrayElementsValueChanged_ThenHashCodesEqualAndValesNotEqual() {
+		String originalHashCode = Integer.toHexString(charPassword.hashCode());
+
+		Arrays.fill(charPassword, '*');
+		String changedHashCode = Integer.toHexString(charPassword.hashCode());
+
+		assertThat(originalHashCode).isEqualTo(changedHashCode);
+		assertThat(charPassword).isNotEqualTo(new char[]{'p', 'a', 's', 's', 'w', 'o', 'r', 'd'});
+	}
+
+	@Test
+	public void whenCallingToStringOfString_ThenValuesEqual() {
+		assertThat(stringPassword.toString()).isEqualTo("password");
+	}
+
+	@Test
+	public void whenCallingToStringOfCharArray_ThenValuesNotEqual() {
+		assertThat(charPassword.toString()).isNotEqualTo("password");
+	}
+}

java-strings/src/test/java/com/baeldung/string/JoinerSplitterUnitTest.java

@@ -0,0 +1,83 @@
+package com.baeldung.string;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static org.junit.Assert.assertEquals;
+
+public class JoinerSplitterUnitTest {
+
+    @Test
+    public void provided_array_convert_to_stream_and_convert_to_string() {
+
+        String[] programming_languages = {"java", "python", "nodejs", "ruby"};
+
+        String expectation = "java,python,nodejs,ruby";
+
+        String result = JoinerSplitter.join(programming_languages);
+        assertEquals(result, expectation);
+    }
+
+    @Test
+    public void givenArray_transformedToStream_convertToPrefixPostfixString() {
+
+        String[] programming_languages = {"java", "python",
+          "nodejs", "ruby"};
+        String expectation = "[java,python,nodejs,ruby]";
+
+        String result = JoinerSplitter.joinWithPrefixPostFix(programming_languages);
+        assertEquals(result, expectation);
+    }
+
+    @Test
+    public void givenString_transformedToStream_convertToList() {
+
+        String programming_languages = "java,python,nodejs,ruby";
+
+        List<String> expectation = new ArrayList<String>();
+        expectation.add("java");
+        expectation.add("python");
+        expectation.add("nodejs");
+        expectation.add("ruby");
+
+        List<String> result = JoinerSplitter.split(programming_languages);
+
+        assertEquals(result, expectation);
+    }
+
+    @Test
+    public void givenString_transformedToStream_convertToListOfChar() {
+
+        String programming_languages = "java,python,nodejs,ruby";
+
+        List<Character> expectation = new ArrayList<Character>();
+        char[] charArray = programming_languages.toCharArray();
+        for (char c : charArray) {
+            expectation.add(c);
+        }
+
+        List<Character> result = JoinerSplitter.splitToListOfChar(programming_languages);
+        assertEquals(result, expectation);
+
+    }
+    
+    @Test
+    public void givenStringArray_transformedToStream_convertToMap() {
+
+        String[] programming_languages = new String[] {"language:java","os:linux","editor:emacs"};
+        
+        Map<String,String> expectation=new HashMap<>();
+        expectation.put("language", "java");
+        expectation.put("os", "linux");
+        expectation.put("editor", "emacs");
+        
+        Map<String, String> result = JoinerSplitter.arrayToMap(programming_languages);
+        assertEquals(result, expectation);
+        
+    }
+
+}

java-strings/src/test/java/com/baeldung/string/ReplaceCharInStringUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.string;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class ReplaceCharInStringUnitTest {
+    private ReplaceCharacterInString characterInString = new ReplaceCharacterInString();
+
+    @Test
+    public void whenReplaceCharAtIndexUsingSubstring_thenSuccess() {
+        assertEquals("abcme", characterInString.replaceCharSubstring("abcde", 'm', 3));
+    }
+
+    @Test
+    public void whenReplaceCharAtIndexUsingCharArray_thenSuccess() {
+        assertEquals("abcme", characterInString.replaceCharUsingCharArray("abcde", 'm', 3));
+    }
+
+    @Test
+    public void whenReplaceCharAtIndexUsingStringBuilder_thenSuccess() {
+        assertEquals("abcme", characterInString.replaceCharStringBuilder("abcde", 'm', 3));
+    }
+
+    @Test
+    public void whenReplaceCharAtIndexUsingStringBuffer_thenSuccess() {
+        assertEquals("abcme", characterInString.replaceCharStringBuffer("abcde", 'm', 3));
+    }
+}

java-strings/src/test/java/com/baeldung/string/StringContainingCharactersUnitTest.java

@@ -0,0 +1,136 @@
+package com.baeldung.string;
+
+import org.junit.Test;
+
+import java.util.regex.Pattern;
+
+import static junit.framework.TestCase.assertFalse;
+import static junit.framework.TestCase.assertTrue;
+
+public class StringContainingCharactersUnitTest {
+
+    private static final Pattern[] inputRegexes = new Pattern[4];
+
+    private static final String regex = "^(?=.*?\\p{Lu})(?=.*?\\p{Ll})(?=.*?\\d)(?=.*?[`~!@#$%^&*()\\-_=+\\\\|\\[{\\]};:'\",<.>/?]).*$";
+
+    static {
+        inputRegexes[0] = Pattern.compile(".*[A-Z].*");
+        inputRegexes[1] = Pattern.compile(".*[a-z].*");
+        inputRegexes[2] = Pattern.compile(".*\\d.*");
+        inputRegexes[3] = Pattern.compile(".*[`~!@#$%^&*()\\-_=+\\\\|\\[{\\]};:'\",<.>/?].*");
+    }
+
+    private static boolean isMatchingRegex(String input) {
+        boolean inputMatches = true;
+        for (Pattern inputRegex : inputRegexes) {
+            if (!inputRegex
+              .matcher(input)
+              .matches()) {
+                inputMatches = false;
+            }
+        }
+        return inputMatches;
+    }
+
+    private static boolean checkString(String input) {
+        String specialChars = "~`!@#$%^&*()-_=+\\|[{]};:'\",<.>/?";
+        char currentCharacter;
+        boolean numberPresent = false;
+        boolean upperCasePresent = false;
+        boolean lowerCasePresent = false;
+        boolean specialCharacterPresent = false;
+
+        for (int i = 0; i < input.length(); i++) {
+            currentCharacter = input.charAt(i);
+            if (Character.isDigit(currentCharacter)) {
+                numberPresent = true;
+            } else if (Character.isUpperCase(currentCharacter)) {
+                upperCasePresent = true;
+            } else if (Character.isLowerCase(currentCharacter)) {
+                lowerCasePresent = true;
+            } else if (specialChars.contains(String.valueOf(currentCharacter))) {
+                specialCharacterPresent = true;
+            }
+        }
+
+        return numberPresent && upperCasePresent && lowerCasePresent && specialCharacterPresent;
+    }
+
+    @Test
+    public void givenRegexes_whenMatchingCorrectString_thenMatches() {
+        String validInput = "Ab3;";
+        assertTrue(isMatchingRegex(validInput));
+    }
+
+    @Test
+    public void givenRegexes_whenMatchingWrongStrings_thenNotMatching() {
+        String invalidInput = "Ab3";
+        assertFalse(isMatchingRegex(invalidInput));
+
+        invalidInput = "Ab;";
+        assertFalse(isMatchingRegex(invalidInput));
+
+        invalidInput = "A3;";
+        assertFalse(isMatchingRegex(invalidInput));
+
+        invalidInput = "b3;";
+        assertFalse(isMatchingRegex(invalidInput));
+    }
+
+    @Test
+    public void givenValidString_whenChecking_thenCorrect() {
+        String validInput = "Ab3;";
+        assertTrue(checkString(validInput));
+    }
+
+    @Test
+    public void givenInvalidStrings_whenChecking_thenNotCorrect() {
+        String invalidInput = "Ab3";
+        assertFalse(checkString(invalidInput));
+
+        invalidInput = "Ab;";
+        assertFalse(checkString(invalidInput));
+
+        invalidInput = "A3;";
+        assertFalse(checkString(invalidInput));
+
+        invalidInput = "b3;";
+        assertFalse(checkString(invalidInput));
+    }
+
+    @Test
+    public void givenSingleRegex_whenMatchingCorrectString_thenMatches() {
+        String validInput = "Ab3;";
+        assertTrue(Pattern
+          .compile(regex)
+          .matcher(validInput)
+          .matches());
+    }
+
+    @Test
+    public void givenSingleRegex_whenMatchingWrongStrings_thenNotMatching() {
+        String invalidInput = "Ab3";
+        assertFalse(Pattern
+          .compile(regex)
+          .matcher(invalidInput)
+          .matches());
+
+        invalidInput = "Ab;";
+        assertFalse(Pattern
+          .compile(regex)
+          .matcher(invalidInput)
+          .matches());
+
+        invalidInput = "A3;";
+        assertFalse(Pattern
+          .compile(regex)
+          .matcher(invalidInput)
+          .matches());
+
+        invalidInput = "b3;";
+        assertFalse(Pattern
+          .compile(regex)
+          .matcher(invalidInput)
+          .matches());
+    }
+}

java-strings/src/test/java/com/baeldung/string/StringEmptyUnitTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.string;
+
+import static org.hamcrest.CoreMatchers.not;
+import static org.hamcrest.text.IsEmptyString.isEmptyOrNullString;
+import static org.hamcrest.text.IsEmptyString.isEmptyString;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNotSame;
+import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertTrue;
+
+import org.apache.commons.lang3.StringUtils;
+import org.assertj.core.api.Assertions;
+import org.junit.Test;
+
+import com.google.common.base.Strings;
+
+public class StringEmptyUnitTest {
+
+    private String text = "baeldung";
+
+    @Test
+    public void givenAString_whenCheckedForEmptyUsingJunit_shouldAssertSuccessfully() {
+        assertTrue(!text.isEmpty());
+        assertFalse(text.isEmpty());
+        assertNotEquals("", text);
+        assertNotSame("", text);
+    }
+
+    @Test
+    public void givenAString_whenCheckedForEmptyUsingHamcrest_shouldAssertSuccessfully() {
+        assertThat(text, not(isEmptyString()));
+        assertThat(text, not(isEmptyOrNullString()));
+    }
+
+    @Test
+    public void givenAString_whenCheckedForEmptyUsingCommonsLang_shouldAssertSuccessfully() {
+        assertTrue(StringUtils.isNotBlank(text));
+    }
+
+    @Test
+    public void givenAString_whenCheckedForEmptyUsingAssertJ_shouldAssertSuccessfully() {
+        Assertions.assertThat(text).isNotEmpty();
+    }
+
+    @Test
+    public void givenAString_whenCheckedForEmptyUsingGuava_shouldAssertSuccessfully() {
+        assertFalse(Strings.isNullOrEmpty(text));
+    }
+
+}

java-strings/src/test/java/com/baeldung/string/StringReplaceAndRemoveUnitTest.java

@@ -0,0 +1,90 @@
+package com.baeldung.string;
+
+import org.apache.commons.lang3.StringUtils;
+import org.apache.commons.lang3.RegExUtils;
+import org.junit.Test;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class StringReplaceAndRemoveUnitTest {
+
+    @Test
+    public void givenTestStrings_whenReplace_thenProcessedString() {
+
+        String master = "Hello World Baeldung!";
+        String target = "Baeldung";
+        String replacement = "Java";
+        String processed = master.replace(target, replacement);
+        assertTrue(processed.contains(replacement));
+        assertFalse(processed.contains(target));
+
+    }
+
+    @Test
+    public void givenTestStrings_whenReplaceAll_thenProcessedString() {
+
+        String master2 = "Welcome to Baeldung, Hello World Baeldung";
+        String regexTarget = "(Baeldung)$";
+        String replacement = "Java";
+        String processed2 = master2.replaceAll(regexTarget, replacement);
+        assertTrue(processed2.endsWith("Java"));
+
+    }
+
+    @Test
+    public void givenTestStrings_whenStringBuilderMethods_thenProcessedString() {
+
+        String master = "Hello World Baeldung!";
+        String target = "Baeldung";
+        String replacement = "Java";
+
+        int startIndex = master.indexOf(target);
+        int stopIndex = startIndex + target.length();
+
+        StringBuilder builder = new StringBuilder(master);
+
+        builder.delete(startIndex, stopIndex);
+        assertFalse(builder.toString()
+            .contains(target));
+
+        builder.replace(startIndex, stopIndex, replacement);
+        assertTrue(builder.toString()
+            .contains(replacement));
+
+    }
+
+    @Test
+    public void givenTestStrings_whenStringUtilsMethods_thenProcessedStrings() {
+
+        String master = "Hello World Baeldung!";
+        String target = "Baeldung";
+        String replacement = "Java";
+
+        String processed = StringUtils.replace(master, target, replacement);
+        assertTrue(processed.contains(replacement));
+
+        String master2 = "Hello World Baeldung!";
+        String target2 = "baeldung";
+        String processed2 = StringUtils.replaceIgnoreCase(master2, target2, replacement);
+        assertFalse(processed2.contains(target));
+
+    }
+
+    @Test
+    public void givenTestStrings_whenReplaceExactWord_thenProcessedString() {
+        String sentence = "A car is not the same as a carriage, and some planes can carry cars inside them!";
+        String regexTarget = "\\bcar\\b";
+        String exactWordReplaced = sentence.replaceAll(regexTarget, "truck");
+        assertTrue("A truck is not the same as a carriage, and some planes can carry cars inside them!".equals(exactWordReplaced));
+    }
+
+    @Test
+    public void givenTestStrings_whenReplaceExactWordUsingRegExUtilsMethod_thenProcessedString() {
+        String sentence = "A car is not the same as a carriage, and some planes can carry cars inside them!";
+        String regexTarget = "\\bcar\\b";
+        String exactWordReplaced = RegExUtils.replaceAll(sentence, regexTarget, "truck");
+        assertTrue("A truck is not the same as a carriage, and some planes can carry cars inside them!".equals(exactWordReplaced));
+    }
+
+}

java-strings/src/test/java/com/baeldung/string/StringUnitTest.java

@@ -0,0 +1,226 @@
+package com.baeldung.string;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.io.UnsupportedEncodingException;
+import java.nio.charset.StandardCharsets;
+import java.util.IllegalFormatException;
+import java.util.regex.PatternSyntaxException;
+
+import org.junit.Test;
+
+public class StringUnitTest {
+
+    @Test
+    public void whenCallCodePointAt_thenDecimalUnicodeReturned() {
+        assertEquals(97, "abcd".codePointAt(0));
+    }
+
+    @Test(expected = StringIndexOutOfBoundsException.class)
+    public void whenPassNonExistingIndex_thenExceptionThrown() {
+        int a = "abcd".codePointAt(4);
+    }
+
+    @Test
+    public void whenCallConcat_thenCorrect() {
+        assertEquals("elephant", "elep".concat("hant"));
+    }
+
+    @Test
+    public void whenGetBytes_thenCorrect() throws UnsupportedEncodingException {
+        byte[] byteArray1 = "abcd".getBytes();
+        byte[] byteArray2 = "efgh".getBytes(StandardCharsets.US_ASCII);
+        byte[] byteArray3 = "ijkl".getBytes("UTF-8");
+        byte[] expected1 = new byte[] { 97, 98, 99, 100 };
+        byte[] expected2 = new byte[] { 101, 102, 103, 104 };
+        byte[] expected3 = new byte[] { 105, 106, 107, 108 };
+
+        assertArrayEquals(expected1, byteArray1);
+        assertArrayEquals(expected2, byteArray2);
+        assertArrayEquals(expected3, byteArray3);
+    }
+
+    @Test
+    public void whenGetBytesUsingASCII_thenCorrect() {
+        byte[] byteArray = "efgh".getBytes(StandardCharsets.US_ASCII);
+        byte[] expected = new byte[] { 101, 102, 103, 104 };
+
+        assertArrayEquals(expected, byteArray);
+    }
+
+    @Test
+    public void whenCreateStringUsingByteArray_thenCorrect() {
+        byte[] array = new byte[] { 97, 98, 99, 100 };
+        String s = new String(array);
+
+        assertEquals("abcd", s);
+    }
+
+    @Test
+    public void whenCallCharAt_thenCorrect() {
+        assertEquals('P', "Paul".charAt(0));
+    }
+
+    @Test(expected = IndexOutOfBoundsException.class)
+    public void whenCharAtOnNonExistingIndex_thenIndexOutOfBoundsExceptionThrown() {
+        char character = "Paul".charAt(4);
+    }
+
+    @Test
+    public void whenCallCodePointCount_thenCorrect() {
+        assertEquals(2, "abcd".codePointCount(0, 2));
+    }
+
+    @Test(expected = IndexOutOfBoundsException.class)
+    public void whenSecondIndexEqualToLengthOfString_thenIndexOutOfBoundsExceptionThrown() {
+        char character = "Paul".charAt(4);
+    }
+
+    @Test
+    public void whenCallContains_thenCorrect() {
+        String s = "abcd";
+
+        assertTrue(s.contains("abc"));
+        assertFalse(s.contains("cde"));
+    }
+
+    @Test
+    public void whenCallCopyValueOf_thenStringConstructed() {
+        char[] array = new char[] { 'a', 'b', 'c', 'd' };
+
+        assertEquals("abcd", String.copyValueOf(array));
+    }
+
+    @Test
+    public void whenCallEndsWith_thenCorrect() {
+        String s1 = "test";
+
+        assertTrue(s1.endsWith("t"));
+    }
+
+    @Test
+    public void whenFormat_thenCorrect() {
+        String value = "Baeldung";
+        String formatted = String.format("Welcome to %s!", value);
+
+        assertEquals("Welcome to Baeldung!", formatted);
+    }
+
+    @Test(expected = IllegalFormatException.class)
+    public void whenInvalidFormatSyntax_thenIllegalFormatExceptionThrown() {
+        String value = "Baeldung";
+        String formatted = String.format("Welcome to %x!", value);
+    }
+
+    @Test
+    public void whenCallIndexOf_thenCorrect() {
+        assertEquals(1, "foo".indexOf("o"));
+    }
+
+    @Test
+    public void whenCallIsEmpty_thenCorrect() {
+        String s1 = "";
+
+        assertTrue(s1.isEmpty());
+    }
+
+    @Test
+    public void whenCallLastIndexOf_thenCorrect() {
+        assertEquals(2, "foo".lastIndexOf("o"));
+        assertEquals(2, "foo".lastIndexOf(111));
+    }
+
+    @Test
+    public void whenCallRegionMatches_thenCorrect() {
+        assertTrue("welcome to baeldung".regionMatches(false, 11, "baeldung", 0, 8));
+    }
+
+    @Test
+    public void whenCallStartsWith_thenCorrect() {
+        assertTrue("foo".startsWith("f"));
+    }
+
+    @Test
+    public void whenTrim_thenCorrect() {
+        assertEquals("foo", " foo  ".trim());
+    }
+
+    @Test
+    public void whenSplit_thenCorrect() {
+        String s = "Welcome to Baeldung";
+        String[] array = new String[] { "Welcome", "to", "Baeldung" };
+
+        assertArrayEquals(array, s.split(" "));
+    }
+
+    @Test(expected = PatternSyntaxException.class)
+    public void whenPassInvalidParameterToSplit_thenPatternSyntaxExceptionThrown() {
+        String s = "Welcome*to Baeldung";
+
+        String[] result = s.split("*");
+    }
+
+    @Test
+    public void whenCallSubSequence_thenCorrect() {
+        String s = "Welcome to Baeldung";
+
+        assertEquals("Welcome", s.subSequence(0, 7));
+    }
+
+    @Test
+    public void whenCallSubstring_thenCorrect() {
+        String s = "Welcome to Baeldung";
+
+        assertEquals("Welcome", s.substring(0, 7));
+    }
+
+    @Test(expected = IndexOutOfBoundsException.class)
+    public void whenSecondIndexEqualToLengthOfString_thenCorrect() {
+        String s = "Welcome to Baeldung";
+
+        String sub = s.substring(0, 20);
+    }
+
+    @Test
+    public void whenConvertToUpperCase_thenCorrect() {
+        String s = "Welcome to Baeldung!";
+
+        assertEquals("WELCOME TO BAELDUNG!", s.toUpperCase());
+    }
+
+    @Test
+    public void whenConvertToLowerCase_thenCorrect() {
+        String s = "WELCOME to BAELDUNG!";
+
+        assertEquals("welcome to baeldung!", s.toLowerCase());
+    }
+
+    @Test
+    public void whenCallReplace_thenCorrect() {
+        String s = "I learn Spanish";
+
+        assertEquals("I learn French", s.replaceAll("Spanish", "French"));
+    }
+
+    @Test
+    public void whenIntern_thenCorrect() {
+        String s1 = "abc";
+        String s2 = new String("abc");
+        String s3 = new String("foo");
+        String s4 = s1.intern();
+        String s5 = s2.intern();
+
+        assertFalse(s3 == s4);
+        assertTrue(s1 == s5);
+    }
+
+    @Test
+    public void whenCallValueOf_thenCorrect() {
+        long l = 200L;
+
+        assertEquals("200", String.valueOf(l));
+    }
+}

java-strings/src/test/java/com/baeldung/string/searching/WordIndexerUnitTest.java

@@ -0,0 +1,62 @@
+package com.baeldung.string.searching;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+
+public class WordIndexerUnitTest {
+
+    String theString;
+    WordIndexer wordIndexer;
+
+    @BeforeEach
+    public void setUp() throws Exception {
+        wordIndexer = new WordIndexer();
+
+        theString = "To be, or not to be: that is the question: "
+          + "Whether 'tis nobler in the mind to suffer "
+          + "The slings and arrows of outrageous fortune, "
+          + "Or to take arms against a sea of troubles, "
+          + "And by opposing end them? To die: to sleep; "
+          + "No more; and by a sleep to say we end "
+          + "The heart-ache and the thousand natural shocks "
+          + "That flesh is heir to, 'tis a consummation "
+          + "Devoutly to be wish'd. To die, to sleep; "
+          + "To sleep: perchance to dream: ay, there's the rub: "
+          + "For in that sleep of death what dreams may come,";
+    }
+
+    @Test
+
+    public void givenWord_whenSearching_thenFindAllIndexedLocations() {
+        List<Integer> expectedResult = Arrays.asList(7, 122, 130, 221, 438);
+
+        List<Integer> actualResult = wordIndexer.findWord(theString, "or");
+
+        assertEquals(expectedResult, actualResult);
+    }
+
+    @Test
+    public void givenWordWithNoRepeatCharacters_whenImprovedSearching_thenFindAllIndexedLocations() {
+        List<Integer> expectedResult = Arrays.asList(7, 122, 130, 221, 438);
+
+        List<Integer> actualResult = wordIndexer.findWordUpgrade(theString, "or");
+
+        assertEquals(expectedResult, actualResult);
+    }
+
+
+    @Test
+    public void givenWord_whenSearching_thenFindAtEndOfString() {
+        List<Integer> expectedResult = Arrays.asList(480);
+
+        List<Integer> actualResult = wordIndexer.findWordUpgrade(theString, "come,");
+
+        assertEquals(expectedResult, actualResult);
+    }
+}

java-strings/src/test/resources/.gitignore

@@ -0,0 +1,13 @@
+*.class
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+
+# Packaged files #
+*.jar
+*.war
+*.ear