Merge remote-tracking branch 'upstream/master'

algorithms-miscellaneous-4/README.md

@@ -11,4 +11,5 @@ This module contains articles about algorithms. Some classes of algorithms, e.g.
 - [Find Substrings That Are Palindromes in Java](https://www.baeldung.com/java-palindrome-substrings)
 - [Find the Longest Substring without Repeating Characters](https://www.baeldung.com/java-longest-substring-without-repeated-characters)
 - [Permutations of an Array in Java](https://www.baeldung.com/java-array-permutations)
+- [Find the Smallest Missing Integer in an Array](https://www.baeldung.com/java-smallest-missing-integer-in-array)
 - More articles: [[<-- prev]](/algorithms-miscellaneous-3) [[next -->]](/algorithms-miscellaneous-5)

algorithms-miscellaneous-5/README.md

@@ -9,4 +9,5 @@ This module contains articles about algorithms. Some classes of algorithms, e.g.
 - [Reversing a Binary Tree in Java](https://www.baeldung.com/java-reversing-a-binary-tree)
 - [Find If Two Numbers Are Relatively Prime in Java](https://www.baeldung.com/java-two-relatively-prime-numbers)
 - [Knapsack Problem Implementation in Java](https://www.baeldung.com/java-knapsack)
+- [How to Determine if a Binary Tree is Balanced](https://www.baeldung.com/java-balanced-binary-tree)
 - More articles: [[<-- prev]](/../algorithms-miscellaneous-4)

aws/src/test/java/com/baeldung/dynamodb/rule/LocalDbCreationRule.java

@@ -15,7 +15,7 @@ public class LocalDbCreationRule extends ExternalResource {
     @Override
     protected void before() throws Exception {
         String port = "8000";
-        this.server = ServerRunner.createServerFromCommandLineArgs(new String[]{"-inMemory", "-port", port});
+        this.server = ServerRunner.createServerFromCommandLineArgs(new String[]{"-inMemory","-sharedDb" ,"-port", port});
         server.start();
     }
 

code-generation/README.md

@@ -7,3 +7,4 @@ This module contains articles about automatic code generation
 - [Introduction to AutoValue](https://www.baeldung.com/introduction-to-autovalue)
 - [Introduction to AutoFactory](https://www.baeldung.com/autofactory)
 - [Google AutoService](https://www.baeldung.com/google-autoservice)
+- [Defensive Copies for Collections Using AutoValue](https://www.baeldung.com/autovalue-defensive-copies)

core-java-modules/core-java-collections-list-3/README.md

@@ -9,4 +9,5 @@ This module contains articles about the Java List collection
 - [List of Primitive Integer Values in Java](https://www.baeldung.com/java-list-primitive-int)
 - [Performance Comparison of Primitive Lists in Java](https://www.baeldung.com/java-list-primitive-performance)
 - [Filtering a Java Collection by a List](https://www.baeldung.com/java-filter-collection-by-list)
+- [How to Count Duplicate Elements in Arraylist](https://www.baeldung.com/java-count-duplicate-elements-arraylist)
 - [[<-- Prev]](/core-java-modules/core-java-collections-list-2)

core-java-modules/core-java-concurrency-advanced-3/pom.xml

@@ -14,11 +14,18 @@
         <relativePath>../../parent-java</relativePath>
     </parent>
 
-    <dependencies>
-    </dependencies>
-
     <build>
         <finalName>core-java-concurrency-advanced-3</finalName>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                </configuration>
+            </plugin>
+        </plugins>
         <resources>
             <resource>
                 <directory>src/main/resources</directory>
@@ -28,6 +35,8 @@
     </build>
 
     <properties>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
     </properties>
 
 </project>

core-java-modules/core-java-concurrency-advanced-3/src/main/java/com/baeldung/commonissues/CollectionsConcurrencyIssues.java

@@ -0,0 +1,53 @@
+package com.baeldung.commonissues;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+public class CollectionsConcurrencyIssues {
+
+    private void putIfAbsentList_NonAtomicOperation_ProneToConcurrencyIssues() {
+        List<String> list = Collections.synchronizedList(new ArrayList<>());
+        if (!list.contains("foo")) {
+            list.add("foo");
+        }
+    }
+
+    private void putIfAbsentList_AtomicOperation_ThreadSafe() {
+        List<String> list = Collections.synchronizedList(new ArrayList<>());
+        synchronized (list) {
+            if (!list.contains("foo")) {
+                list.add("foo");
+            }
+        }
+    }
+
+    private void putIfAbsentMap_NonAtomicOperation_ProneToConcurrencyIssues() {
+        Map<String, String> map = new ConcurrentHashMap<>();
+        if (!map.containsKey("foo")) {
+            map.put("foo", "bar");
+        }
+    }
+
+    private void putIfAbsentMap_AtomicOperation_BetterApproach() {
+        Map<String, String> map = new ConcurrentHashMap<>();
+        synchronized (map) {
+            if (!map.containsKey("foo")) {
+                map.put("foo", "bar");
+            }
+        }
+    }
+
+    private void putIfAbsentMap_AtomicOperation_BestApproach() {
+        Map<String, String> map = new ConcurrentHashMap<>();
+        map.putIfAbsent("foo", "bar");
+    }
+
+    private void computeIfAbsentMap_AtomicOperation() {
+        Map<String, String> map = new ConcurrentHashMap<>();
+        map.computeIfAbsent("foo", key -> key + "bar");
+    }
+
+}

core-java-modules/core-java-concurrency-advanced-3/src/main/java/com/baeldung/commonissues/Counter.java

@@ -0,0 +1,13 @@
+package com.baeldung.commonissues;
+
+class Counter {
+    private int counter = 0;
+
+    public void increment() {
+        counter++;
+    }
+
+    public int getValue() {
+        return counter;
+    }
+}

core-java-modules/core-java-concurrency-advanced-3/src/main/java/com/baeldung/commonissues/DeadlockExample.java

@@ -0,0 +1,42 @@
+package com.baeldung.commonissues;
+
+public class DeadlockExample {
+
+    public static Object lock1 = new Object();
+    public static Object lock2 = new Object();
+
+    public static void main(String args[]) {
+        Thread threadA = new Thread(() -> {
+            synchronized (lock1) {
+                System.out.println("ThreadA: Holding lock 1...");
+                sleep();
+                System.out.println("ThreadA: Waiting for lock 2...");
+
+                synchronized (lock2) {
+                    System.out.println("ThreadA: Holding lock 1 & 2...");
+                }
+            }
+        });
+        Thread threadB = new Thread(() -> {
+            synchronized (lock2) {
+                System.out.println("ThreadB: Holding lock 2...");
+                sleep();
+                System.out.println("ThreadB: Waiting for lock 1...");
+
+                synchronized (lock1) {
+                    System.out.println("ThreadB: Holding lock 1 & 2...");
+                }
+            }
+        });
+        threadA.start();
+        threadB.start();
+    }
+
+    private static void sleep() {
+        try {
+            Thread.sleep(100);
+        } catch (InterruptedException e) {
+            throw new RuntimeException();
+        }
+    }
+}

core-java-modules/core-java-concurrency-advanced-3/src/main/java/com/baeldung/commonissues/SimpleDateFormatThreadUnsafetyExample.java

@@ -0,0 +1,35 @@
+package com.baeldung.commonissues;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+public class SimpleDateFormatThreadUnsafetyExample {
+
+    private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
+
+    public static void main(String[] args) {
+        String dateStr = "2019-10-29T11:12:21";
+
+        ExecutorService executorService = Executors.newFixedThreadPool(10);
+
+        for (int i = 0; i < 20; i++) {
+            executorService.submit(() -> parseDate(dateStr));
+        }
+
+        executorService.shutdown();
+    }
+
+    private static void parseDate(String dateStr) {
+        try {
+            Date date = simpleDateFormat.parse(dateStr);
+            System.out.println("Successfully Parsed Date " + date);
+        } catch (ParseException e) {
+            System.out.println("ParseError " + e.getMessage());
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+}

core-java-modules/core-java-concurrency-advanced-3/src/main/java/com/baeldung/commonissues/SynchronizedCounter.java

@@ -0,0 +1,13 @@
+package com.baeldung.commonissues;
+
+class SynchronizedCounter {
+    private int counter = 0;
+
+    public synchronized void increment() {
+        counter++;
+    }
+
+    public synchronized int getValue() {
+        return counter;
+    }
+}

core-java-modules/core-java-concurrency-advanced-3/src/main/java/com/baeldung/commonissues/SynchronizedVolatileCounter.java

@@ -0,0 +1,13 @@
+package com.baeldung.commonissues;
+
+class SynchronizedVolatileCounter {
+    private volatile int counter = 0;
+
+    public synchronized void increment() {
+        counter++;
+    }
+
+    public int getValue() {
+        return counter;
+    }
+}

core-java-modules/core-java-date-operations/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles:
+- [Get the Current Date Prior to Java 8](https://www.baeldung.com/java-get-the-current-date-legacy)
+- [Skipping Weekends While Adding Days to LocalDate in Java 8](https://www.baeldung.com/java-localdate-add-days-skip-weekends)

core-java-modules/core-java-datetime-java8/README.md

@@ -13,3 +13,4 @@ This module contains articles about the Date and Time API introduced with Java 8
 - [How to Get the Start and the End of a Day using Java](http://www.baeldung.com/java-day-start-end)
 - [Set the Time Zone of a Date in Java](https://www.baeldung.com/java-set-date-time-zone)
 - [Comparing Dates in Java](https://www.baeldung.com/java-comparing-dates)
+- [Generating Random Dates in Java](https://www.baeldung.com/java-random-dates)

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

@@ -17,3 +17,4 @@ This module contains articles about core java exceptions
 - [Common Java Exceptions](https://www.baeldung.com/java-common-exceptions)
 - [Throw Exception in Optional in Java 8](https://www.baeldung.com/java-optional-throw-exception)
 - [How to Find an Exception’s Root Cause in Java](https://www.baeldung.com/java-exception-root-cause)
+- [Is It a Bad Practice to Catch Throwable?](https://www.baeldung.com/java-catch-throwable-bad-practice)

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

@@ -5,4 +5,5 @@ This module contains articles about core features in the Java language
 ### Relevant Articles: 
 - [Java Primitives versus Objects](https://www.baeldung.com/java-primitives-vs-objects)
 - [Command-Line Arguments in Java](https://www.baeldung.com/java-command-line-arguments)
+- [What is a POJO Class?](https://www.baeldung.com/java-pojo-class)
 - [[<-- Prev]](/core-java-modules/core-java-lang)

core-java-modules/core-java-lang-math/README.md

@@ -6,3 +6,4 @@
 - [Java 8 Math New Methods](https://www.baeldung.com/java-8-math)
 - [Java 8 Unsigned Arithmetic Support](https://www.baeldung.com/java-unsigned-arithmetic)
 - [How to Separate Double into Integer and Decimal Parts](https://www.baeldung.com/java-separate-double-into-integer-decimal-parts)
+- [The strictfp Keyword in Java](https://www.baeldung.com/java-strictfp)

core-java-modules/core-java-streams-3/README.md

@@ -8,4 +8,5 @@ This module contains articles about the Stream API in Java.
 - [The Difference Between Collection.stream().forEach() and Collection.forEach()](https://www.baeldung.com/java-collection-stream-foreach)
 - [Guide to Java 8’s Collectors](https://www.baeldung.com/java-8-collectors)
 - [Primitive Type Streams in Java 8](https://www.baeldung.com/java-8-primitive-streams)
-- More articles: [[<-- prev>]](/../core-java-streams-2)
+- [Debugging Java 8 Streams with IntelliJ](https://www.baeldung.com/intellij-debugging-java-streams)
+- More articles: [[<-- prev>]](/../core-java-streams-2)

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

@@ -58,7 +58,7 @@
     </build>
 
     <properties>
-        <commons-lang3.version>3.8.1</commons-lang3.version>
+        <commons-lang3.version>3.9</commons-lang3.version>
         <assertj.version>3.6.1</assertj.version>
         <commons-codec.version>1.10</commons-codec.version>
     </properties>

core-java-modules/core-java-string-operations/src/main/java/com/baeldung/isnumeric/Benchmarking.java

@@ -1,6 +1,9 @@
 package com.baeldung.isnumeric;
 
+import java.util.HashMap;
+import java.util.Map;
 import java.util.concurrent.TimeUnit;
+import java.util.function.Function;
 
 import org.openjdk.jmh.annotations.Benchmark;
 import org.openjdk.jmh.annotations.BenchmarkMode;
@@ -14,6 +17,8 @@ import org.openjdk.jmh.runner.options.Options;
 import org.openjdk.jmh.runner.options.OptionsBuilder;
 
 public class Benchmarking {
+    private static final TestMode MODE = TestMode.DIVERS;
+
     public static void main(String[] args) throws RunnerException {
         Options opt = new OptionsBuilder().include(Benchmarking.class.getSimpleName())
             .forks(1)
@@ -22,52 +27,89 @@ public class Benchmarking {
         new Runner(opt).run();
     }
 
+    private static final IsNumeric subject = new IsNumeric();
+
     @State(Scope.Thread)
     public static class ExecutionPlan {
-        public String number = Integer.toString(Integer.MAX_VALUE);
-        public boolean isNumber = false;
-        public IsNumeric isNumeric = new IsNumeric();
+        private final Map<String, Boolean> testPlan = testPlan();
+
+        void validate(Function<String, Boolean> functionUnderTest) {
+            testPlan.forEach((key, value) -> {
+                Boolean result = functionUnderTest.apply(key);
+
+                assertEquals(value, result, key);
+            });
+        }
+
+        private void assertEquals(Boolean expectedResult, Boolean result, String input) {
+            if (result != expectedResult) {
+                throw new IllegalStateException("The output does not match the expected output, for input: " + input);
+            }
+        }
+
+        private Map<String, Boolean> testPlan() {
+            HashMap<String, Boolean> plan = new HashMap<>();
+            plan.put(Integer.toString(Integer.MAX_VALUE), true);
+
+            if (MODE == TestMode.SIMPLE) {
+                return plan;
+            }
+
+            plan.put("x0", false);
+            plan.put("0..005", false);
+            plan.put("--11", false);
+            plan.put("test", false);
+            plan.put(null, false);
+            for (int i = 0; i < 94; i++) {
+                plan.put(Integer.toString(i), true);
+            }
+            return plan;
+        }
     }
 
     @Benchmark
     @BenchmarkMode(Mode.AverageTime)
     @OutputTimeUnit(TimeUnit.NANOSECONDS)
     public void usingCoreJava(ExecutionPlan plan) {
-        plan.isNumber = plan.isNumeric.usingCoreJava(plan.number);
+        plan.validate(subject::usingCoreJava);
     }
 
     @Benchmark
     @BenchmarkMode(Mode.AverageTime)
     @OutputTimeUnit(TimeUnit.NANOSECONDS)
     public void usingRegularExpressions(ExecutionPlan plan) {
-        plan.isNumber = plan.isNumeric.usingRegularExpressions(plan.number);
+        plan.validate(subject::usingPreCompiledRegularExpressions);
     }
 
     @Benchmark
     @BenchmarkMode(Mode.AverageTime)
     @OutputTimeUnit(TimeUnit.NANOSECONDS)
     public void usingNumberUtils_isCreatable(ExecutionPlan plan) {
-        plan.isNumber = plan.isNumeric.usingNumberUtils_isCreatable(plan.number);
+        plan.validate(subject::usingNumberUtils_isCreatable);
     }
 
     @Benchmark
     @BenchmarkMode(Mode.AverageTime)
     @OutputTimeUnit(TimeUnit.NANOSECONDS)
     public void usingNumberUtils_isParsable(ExecutionPlan plan) {
-        plan.isNumber = plan.isNumeric.usingNumberUtils_isParsable(plan.number);
+        plan.validate(subject::usingNumberUtils_isParsable);
     }
 
     @Benchmark
     @BenchmarkMode(Mode.AverageTime)
     @OutputTimeUnit(TimeUnit.NANOSECONDS)
     public void usingStringUtils_isNumeric(ExecutionPlan plan) {
-        plan.isNumber = plan.isNumeric.usingStringUtils_isNumeric(plan.number);
+        plan.validate(subject::usingStringUtils_isNumeric);
     }
 
     @Benchmark
     @BenchmarkMode(Mode.AverageTime)
     @OutputTimeUnit(TimeUnit.NANOSECONDS)
     public void usingStringUtils_isNumericSpace(ExecutionPlan plan) {
-        plan.isNumber = plan.isNumeric.usingStringUtils_isNumericSpace(plan.number);
+        plan.validate(subject::usingStringUtils_isNumericSpace);
+    }
+
+    private enum TestMode {
+        SIMPLE, DIVERS
     }
 }

core-java-modules/core-java-string-operations/src/main/java/com/baeldung/isnumeric/IsNumeric.java

@@ -1,20 +1,33 @@
 package com.baeldung.isnumeric;
 
+import java.util.regex.Pattern;
+
 import org.apache.commons.lang3.StringUtils;
 import org.apache.commons.lang3.math.NumberUtils;
 
 public class IsNumeric {
+    private final Pattern pattern = Pattern.compile("-?\\d+(\\.\\d+)?");
+
     public boolean usingCoreJava(String strNum) {
+        if (strNum == null) {
+            return false;
+        }
+
         try {
             Double.parseDouble(strNum);
-        } catch (NumberFormatException | NullPointerException nfe) {
+        } catch (NumberFormatException nfe) {
             return false;
         }
         return true;
     }
 
-    public boolean usingRegularExpressions(String strNum) {
-        return strNum.matches("-?\\d+(\\.\\d+)?");
+    public boolean usingPreCompiledRegularExpressions(String strNum) {
+        if (strNum == null) {
+            return false;
+        }
+
+        return pattern.matcher(strNum)
+            .matches();
     }
 
     public boolean usingNumberUtils_isCreatable(String strNum) {

core-java-modules/core-java-string-operations/src/main/java/com/baeldung/isnumeric/IsNumericDriver.java

@@ -13,8 +13,8 @@ public class IsNumericDriver {
         boolean res = isNumeric.usingCoreJava("1001");
         LOG.info("Using Core Java : " + res);
 
-        res = isNumeric.usingRegularExpressions("1001");
-        LOG.info("Using Regular Expressions : " + res);
+        res = isNumeric.usingPreCompiledRegularExpressions("1001");
+        LOG.info("Using Pre-compiled Regular Expressions : " + res);
 
         res = isNumeric.usingNumberUtils_isCreatable("1001");
         LOG.info("Using NumberUtils.isCreatable : " + res);

core-java-modules/core-java-string-operations/src/test/java/com/baeldung/isnumeric/CoreJavaIsNumericUnitTest.java

@@ -6,9 +6,13 @@ import org.junit.Test;
 
 public class CoreJavaIsNumericUnitTest {
     public static boolean isNumeric(String strNum) {
+        if (strNum == null) {
+            return false;
+        }
+
         try {
-            double d = Double.parseDouble(strNum);
-        } catch (NumberFormatException | NullPointerException nfe) {
+            Double.parseDouble(strNum);
+        } catch (NumberFormatException nfe) {
             return false;
         }
         return true;

core-java-modules/core-java-string-operations/src/test/java/com/baeldung/isnumeric/RegularExpressionsUnitTest.java

@@ -2,11 +2,19 @@ package com.baeldung.isnumeric;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+import java.util.regex.Pattern;
+
 import org.junit.Test;
 
 public class RegularExpressionsUnitTest {
-    public static boolean isNumeric(String strNum) {
-        return strNum.matches("-?\\d+(\\.\\d+)?");
+    private final Pattern pattern = Pattern.compile("-?\\d+(\\.\\d+)?");
+
+    public boolean isNumeric(String strNum) {
+        if (strNum == null) {
+            return false;
+        }
+        return pattern.matcher(strNum)
+            .matches();
     }
 
     @Test
@@ -17,6 +25,7 @@ public class RegularExpressionsUnitTest {
         assertThat(isNumeric("-200")).isTrue();
 
         // Invalid Numbers
+        assertThat(isNumeric(null)).isFalse();
         assertThat(isNumeric("abc")).isFalse();
     }
 }

jackson-2/pom.xml

@@ -14,14 +14,6 @@
 
     <dependencies>
 
-        <!-- marshalling -->
-
-        <dependency>
-            <groupId>com.fasterxml.jackson.core</groupId>
-            <artifactId>jackson-databind</artifactId>
-            <version>${jackson.version}</version>
-        </dependency>
-
         <!-- YAML -->
         <dependency>
             <groupId>com.fasterxml.jackson.dataformat</groupId>

jackson-annotations/README.md

@@ -0,0 +1,11 @@
+## Jackson Annotations
+
+This module contains articles about Jackson annotations.
+
+### Relevant Articles: 
+- [Guide to @JsonFormat in Jackson](https://www.baeldung.com/jackson-jsonformat)
+- [More Jackson Annotations](https://www.baeldung.com/jackson-advanced-annotations)
+- [Jackson Annotation Examples](https://www.baeldung.com/jackson-annotations)
+- [Jackson – Bidirectional Relationships](https://www.baeldung.com/jackson-bidirectional-relationships-and-infinite-recursion)
+- [Jackson – Change Name of Field](https://www.baeldung.com/jackson-name-of-property)
+- [Jackson Ignore Properties on Marshalling](https://www.baeldung.com/jackson-ignore-properties-on-serialization)

jackson-annotations/pom.xml

@@ -0,0 +1,60 @@
+<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>jackson-annotations</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>jackson-annotations</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>${jackson.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.dataformat</groupId>
+            <artifactId>jackson-dataformat-xml</artifactId>
+            <version>${jackson.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.module</groupId>
+            <artifactId>jackson-module-jsonSchema</artifactId>
+            <version>${jackson.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>io.rest-assured</groupId>
+            <artifactId>json-path</artifactId>
+            <version>${rest-assured.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>jackson-annotations</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+    <properties>
+        <assertj.version>3.11.0</assertj.version>
+        <rest-assured.version>3.1.1</rest-assured.version>
+    </properties>
+
+</project>