Merge remote-tracking branch 'upstream/master'

.gitignore

@@ -65,6 +65,7 @@ core-java-io/target_link.txt
 core-java/src/main/java/com/baeldung/manifest/MANIFEST.MF
 ethereum/logs/
 jmeter/src/main/resources/*-JMeter.csv
+ninja/devDb.mv.db
 
 **/node_modules/
 **/dist

algorithms-miscellaneous-5/README.md

@@ -16,4 +16,8 @@ This module contains articles about algorithms. Some classes of algorithms, e.g.
 - [Maximum Subarray Problem](https://www.baeldung.com/java-maximum-subarray)
 - [How to Merge Two Sorted Arrays](https://www.baeldung.com/java-merge-sorted-arrays)
 - [Median of Stream of Integers using Heap](https://www.baeldung.com/java-stream-integers-median-using-heap)
+- [Kruskal’s Algorithm for Spanning Trees](https://www.baeldung.com/java-spanning-trees-kruskal)
+- [Balanced Brackets Algorithm in Java](https://www.baeldung.com/java-balanced-brackets-algorithm)
+- [Efficiently Merge Sorted Java Sequences](https://www.baeldung.com/java-merge-sorted-sequences)
+- [Introduction to Greedy Algorithms with Java](https://www.baeldung.com/java-greedy-algorithms)
 - More articles: [[<-- prev]](/../algorithms-miscellaneous-4)

algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/balancedbinarytree/AVLTree.java

@@ -0,0 +1,141 @@
+package com.baeldung.algorithms.balancedbinarytree;
+
+public class AVLTree {
+
+    public class Node {
+        int key;
+        int height;
+        Node left;
+        Node right;
+
+        Node(int key) {
+            this.key = key;
+        }
+    }
+
+    private Node root;
+
+    public Node find(int key) {
+        Node current = root;
+        while (current != null) {
+            if (current.key == key) {
+               break;
+            }
+            current = current.key < key ? current.right : current.left;
+        }
+        return current;
+    }
+
+    public void insert(int key) {
+        root = insert(root, key);
+    }
+
+    public void delete(int key) {
+        root = delete(root, key);
+    }
+
+    public Node getRoot() {
+        return root;
+    }
+
+    public int height() {
+        return root == null ? -1 : root.height;
+    }
+
+    private Node insert(Node node, int key) {
+        if (node == null) {
+            return new Node(key);
+        } else if (node.key > key) {
+            node.left = insert(node.left, key);
+        } else if (node.key < key) {
+            node.right = insert(node.right, key);
+        } else {
+            throw new RuntimeException("duplicate Key!");
+        }
+        return rebalance(node);
+    }
+
+    private Node delete(Node node, int key) {
+        if (node == null) {
+            return node;
+        } else if (node.key > key) {
+            node.left = delete(node.left, key);
+        } else if (node.key < key) {
+            node.right = delete(node.right, key);
+        } else {
+            if (node.left == null || node.right == null) {
+                node = (node.left == null) ? node.right : node.left;
+            } else {
+                Node mostLeftChild = mostLeftChild(node.right);
+                node.key = mostLeftChild.key;
+                node.right = delete(node.right, node.key);
+            }
+        }
+        if (node != null) {
+            node = rebalance(node);
+        }
+        return node;
+    }
+
+    private Node mostLeftChild(Node node) {
+        Node current = node;
+        /* loop down to find the leftmost leaf */
+        while (current.left != null) {
+            current = current.left;
+        }
+        return current;
+    }
+
+    private Node rebalance(Node z) {
+        updateHeight(z);
+        int balance = getBalance(z);
+        if (balance > 1) {
+            if (height(z.right.right) > height(z.right.left)) {
+                z = rotateLeft(z);
+            } else {
+                z.right = rotateRight(z.right);
+                z = rotateLeft(z);
+            }
+        } else if (balance < -1) {
+            if (height(z.left.left) > height(z.left.right)) {
+                z = rotateRight(z);
+            } else {
+                z.left = rotateLeft(z.left);
+                z = rotateRight(z);
+            }
+        }
+        return z;
+    }
+
+    private Node rotateRight(Node y) {
+        Node x = y.left;
+        Node z = x.right;
+        x.right = y;
+        y.left = z;
+        updateHeight(y);
+        updateHeight(x);
+        return x;
+    }
+
+    private Node rotateLeft(Node y) {
+        Node x = y.right;
+        Node z = x.left;
+        x.left = y;
+        y.right = z;
+        updateHeight(y);
+        updateHeight(x);
+        return x;
+    }
+
+    private void updateHeight(Node n) {
+        n.height = 1 + Math.max(height(n.left), height(n.right));
+    }
+
+    private int height(Node n) {
+        return n == null ? -1 : n.height;
+    }
+
+    public int getBalance(Node n) {
+        return (n == null) ? 0 : height(n.right) - height(n.left);
+    }
+}

algorithms-miscellaneous-5/src/test/java/com/baeldung/algorithms/balancedbinarytree/AVLTreeUnitTest.java

@@ -0,0 +1,83 @@
+package com.baeldung.algorithms.balancedbinarytree;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class AVLTreeUnitTest {
+
+    @Test
+    public void givenEmptyTree_whenHeightCalled_shouldReturnMinus1() {
+        AVLTree tree = new AVLTree();
+        Assert.assertEquals(-1, tree.height());
+    }
+
+    @Test
+    public void givenEmptyTree_whenInsertCalled_heightShouldBeZero() {
+        AVLTree tree = new AVLTree();
+        tree.insert(1);
+        Assert.assertEquals(0, tree.height());
+    }
+
+    @Test
+    public void givenEmptyTree_whenInsertCalled_treeShouldBeAvl() {
+        AVLTree tree = new AVLTree();
+        tree.insert(1);
+        Assert.assertTrue(isAVL(tree));
+    }
+
+    @Test
+    public void givenSampleTree_whenInsertCalled_treeShouldBeAvl() {
+        AVLTree tree = getSampleAVLTree();
+        int newKey = 11;
+        tree.insert(newKey);
+        Assert.assertTrue(isAVL(tree));
+    }
+
+    @Test
+    public void givenSampleTree_whenFindExistingKeyCalled_shouldReturnMatchedNode() {
+        AVLTree tree = getSampleAVLTree();
+        int existingKey = 2;
+        AVLTree.Node result = tree.find(existingKey);
+        Assert.assertEquals(result.key, existingKey);
+    }
+
+    @Test
+    public void givenSampleTree_whenFindNotExistingKeyCalled_shouldReturnNull() {
+        AVLTree tree = getSampleAVLTree();
+        int notExistingKey = 11;
+        AVLTree.Node result = tree.find(notExistingKey);
+        Assert.assertNull(result);
+    }
+
+    @Test
+    public void givenEmptyTree_whenDeleteCalled_treeShouldBeAvl() {
+        AVLTree tree = new AVLTree();
+        tree.delete(1);
+        Assert.assertTrue(isAVL(tree));
+    }
+
+    @Test
+    public void givenSampleTree_whenDeleteCalled_treeShouldBeAvl() {
+        AVLTree tree = getSampleAVLTree();
+        tree.delete(1);
+        Assert.assertTrue(isAVL(tree, tree.getRoot()));
+    }
+
+    private boolean isAVL(AVLTree tree) {
+       return isAVL(tree, tree.getRoot());
+    }
+
+    private boolean isAVL(AVLTree tree, AVLTree.Node node) {
+        if ( node == null )
+            return true;
+        int balance = tree.getBalance(node);
+        return (balance <= 1 && balance >= -1) && isAVL(tree, node.left) && isAVL(tree, node.right);
+    }
+
+    private AVLTree getSampleAVLTree() {
+        AVLTree avlTree = new AVLTree();
+        for (int i = 0; i < 10; i++)
+            avlTree.insert(i);
+        return avlTree;
+    }
+}

algorithms-sorting-2/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles:
+
+- [Partitioning and Sorting Arrays with Many Repeated Entries](https://www.baeldung.com/java-sorting-arrays-with-repeated-entries)

apache-poi/README.md

@@ -6,3 +6,6 @@ This module contains articles about Apache POI
 - [Microsoft Word Processing in Java with Apache POI](https://www.baeldung.com/java-microsoft-word-with-apache-poi)
 - [Working with Microsoft Excel in Java](https://www.baeldung.com/java-microsoft-excel)
 - [Creating a MS PowerPoint Presentation in Java](https://www.baeldung.com/apache-poi-slideshow)
+- [Merge Cells in Excel Using Apache POI](https://www.baeldung.com/java-apache-poi-merge-cells)
+- [Get String Value of Excel Cell with Apache POI](https://www.baeldung.com/java-apache-poi-cell-string-value)
+- [Read Excel Cell Value Rather Than Formula With Apache POI](https://github.com/eugenp/tutorials/tree/master/apache-poi)

apache-poi/src/test/java/com/baeldung/poi/excel/merge/ExcelCellMergerUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.poi.excel;
+package com.baeldung.poi.excel.merge;
 
 import static org.junit.Assert.assertEquals;
 

apache-rocketmq/README.md

@@ -3,3 +3,5 @@
 This module contains articles about Apache RocketMQ
 
 ### Relevant Articles: 
+
+- [Apache RocketMQ with Spring Boot](https://www.baeldung.com/apache-rocketmq-spring-boot)

core-java-modules/core-java-13/README.md

@@ -1,3 +1,4 @@
 ### Relevant articles:
 
 - [Java Switch Statement](https://www.baeldung.com/java-switch)
+- [New Java 13 Features](https://www.baeldung.com/java-13-new-features)

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

@@ -13,4 +13,5 @@ This module contains articles about Java arrays
 - [Removing an Element from an Array in Java](https://www.baeldung.com/java-array-remove-element)
 - [Removing the First Element of an Array](https://www.baeldung.com/java-array-remove-first-element)
 - [Adding an Element to a Java Array vs an ArrayList](https://www.baeldung.com/java-add-element-to-array-vs-list)
+- [Arrays.sort vs Arrays.parallelSort](https://www.baeldung.com/java-arrays-sort-vs-parallelsort)
 - [[<-- Prev]](/core-java-modules/core-java-arrays)

core-java-modules/core-java-arrays-2/src/test/java/com/baeldung/arraysort/SortComparisonUnitTest.java

@@ -69,7 +69,7 @@ public class SortComparisonUnitTest {
     }
 
     @Test
-    public void givenArrayOfIntegers_whenUsingArraysSortMethodWithRange_thenSortRangeOfArrayInAscendingOrder() {
+    public void givenArrayOfIntegers_whenUsingArraysSortWithRange_thenSortRangeOfArrayAsc() {
         int[] array = { 10, 4, 6, 2, 1, 9, 7, 8, 3, 5 };
         int[] expected = { 10, 4, 1, 2, 6, 7, 8, 9, 3, 5 };
 
@@ -89,7 +89,7 @@ public class SortComparisonUnitTest {
     }
 
     @Test
-    public void givenArrayOfIntegers_whenUsingArraysParallelSortMethodWithRange_thenSortRangeOfArrayInAscendingOrder() {
+    public void givenArrayOfIntegers_whenUsingArraysParallelSortWithRange_thenSortRangeOfArrayAsc() {
         int[] array = { 10, 4, 6, 2, 1, 9, 7, 8, 3, 5 };
         int[] expected = { 10, 4, 1, 2, 6, 7, 8, 9, 3, 5 };
 

core-java-modules/core-java-concurrency-advanced-3/README.md

@@ -8,4 +8,6 @@ This module contains articles about advanced topics about multithreading with co
 
 - [Common Concurrency Pitfalls in Java](https://www.baeldung.com/java-common-concurrency-pitfalls)
 - [Guide to RejectedExecutionHandler](https://www.baeldung.com/java-rejectedexecutionhandler)
-[[<-- previous]](/core-java-modules/core-java-concurrency-advanced-2)
+- [Guide to Work Stealing in Java](https://www.baeldung.com/java-work-stealing)
+- [Asynchronous Programming in Java](https://www.baeldung.com/java-asynchronous-programming)
+- [[<-- previous]](/core-java-modules/core-java-concurrency-advanced-2)

core-java-modules/core-java-concurrency-advanced/src/main/java/com/baeldung/concurrent/volatilekeyword/SharedObject.java

@@ -4,7 +4,7 @@ package com.baeldung.concurrent.volatilekeyword;
 public class SharedObject {
     private volatile int count=0;
 
-    void increamentCount(){
+    void incrementCount(){
         count++;
     }
     public int  getCount(){

core-java-modules/core-java-concurrency-advanced/src/test/java/com/baeldung/concurrent/volatilekeyword/SharedObjectManualTest.java

@@ -10,7 +10,7 @@ public class SharedObjectManualTest {
     public void whenOneThreadWrites_thenVolatileReadsFromMainMemory() throws InterruptedException {
         SharedObject sharedObject = new SharedObject();
 
-        Thread writer = new Thread(() -> sharedObject.increamentCount());
+        Thread writer = new Thread(() -> sharedObject.incrementCount());
         writer.start();
         Thread.sleep(100);
 
@@ -31,11 +31,11 @@ public class SharedObjectManualTest {
     @Test
     public void whenTwoThreadWrites_thenVolatileReadsFromMainMemory() throws InterruptedException {
         SharedObject sharedObject = new SharedObject();
-        Thread writerOne = new Thread(() -> sharedObject.increamentCount());
+        Thread writerOne = new Thread(() -> sharedObject.incrementCount());
         writerOne.start();
         Thread.sleep(100);
 
-        Thread writerTwo = new Thread(() -> sharedObject.increamentCount());
+        Thread writerTwo = new Thread(() -> sharedObject.incrementCount());
         writerTwo.start();
         Thread.sleep(100);
 

core-java-modules/core-java-date-operations-2/README.md

@@ -6,4 +6,5 @@ This module contains articles about date operations in Java.
 - [Skipping Weekends While Adding Days to LocalDate in Java 8](https://www.baeldung.com/java-localdate-add-days-skip-weekends)
 - [Checking If Two Java Dates Are on the Same Day](https://www.baeldung.com/java-check-two-dates-on-same-day)
 - [Converting Java Date to OffsetDateTime](https://www.baeldung.com/java-convert-date-to-offsetdatetime)
+- [How to Set the JVM Time Zone](https://www.baeldung.com/java-jvm-time-zone)
 - [[<-- Prev]](/core-java-modules/core-java-date-operations-1)

core-java-modules/core-java-datetime-java8-2/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles:
+
+- [Creating a LocalDate with Values in Java](https://www.baeldung.com/java-creating-localdate-with-values)

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

@@ -6,3 +6,4 @@ This module contains articles about core java exceptions
 
 - [Is It a Bad Practice to Catch Throwable?](https://www.baeldung.com/java-catch-throwable-bad-practice)
 - [Wrapping vs Rethrowing Exceptions in Java](https://www.baeldung.com/java-wrapping-vs-rethrowing-exceptions)
+- [java.net.UnknownHostException: Invalid Hostname for Server](https://www.baeldung.com/java-unknownhostexception)

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/socketexception/SocketClient.java

@@ -0,0 +1,32 @@
+package com.baeldung.socketexception;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.net.Socket;
+
+public class SocketClient {
+
+    private Socket clientSocket;
+    private PrintWriter out;
+    private BufferedReader in;
+
+    public void startConnection(String ip, int port) throws IOException {
+        clientSocket = new Socket(ip, port);
+        out = new PrintWriter(clientSocket.getOutputStream(), true);
+        in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
+    }
+
+    public String sendMessage(String msg) throws IOException {
+        out.println(msg);
+        return in.readLine();
+    }
+
+    public void stopConnection() throws IOException {
+        in.close();
+        out.close();
+        clientSocket.close();
+    }
+
+}

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/socketexception/SocketServer.java

@@ -0,0 +1,45 @@
+package com.baeldung.socketexception;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.net.ServerSocket;
+import java.net.Socket;
+
+public class SocketServer {
+
+    private ServerSocket serverSocket;
+    private Socket clientSocket;
+    private PrintWriter out;
+    private BufferedReader in;
+
+    public void start(int port) {
+        try {
+            serverSocket = new ServerSocket(port);
+            clientSocket = serverSocket.accept();
+            out = new PrintWriter(clientSocket.getOutputStream(), true);
+            in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
+            String msg = in.readLine();
+            if (msg.contains("hi"))
+                out.println("hi");
+            else
+                out.println("didn't understand");
+            close();
+            stop();
+        } catch (IOException e) {
+            
+        }
+    }
+
+    private void close() throws IOException {
+        in.close();
+        out.close();
+    }
+
+    private void stop() throws IOException {
+        clientSocket.close();
+        serverSocket.close();
+    }
+
+}

core-java-modules/core-java-exceptions-2/src/test/java/com/baeldung/socketexception/SocketExceptionHandlingUnitTest.java

@@ -0,0 +1,31 @@
+package com.baeldung.socketexception;
+
+import java.io.IOException;
+import java.net.SocketException;
+import java.util.concurrent.Executors;
+
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class SocketExceptionHandlingUnitTest {
+
+    @BeforeClass
+    public static void runServer() throws IOException, InterruptedException {
+        Executors.newSingleThreadExecutor()
+            .submit(() -> new SocketServer().start(6699));
+        Thread.sleep(100);
+    }
+
+    @Test
+    public void givenRunningServer_whenConnectToClosedSocket_thenHandleException() throws IOException {
+        SocketClient client = new SocketClient();
+        client.startConnection("127.0.0.1", 6699);
+        try {
+            client.sendMessage("hi");
+            client.sendMessage("hi again");
+        } catch (SocketException e) {
+            client.stopConnection();
+        }
+    }
+
+}

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

@@ -7,4 +7,6 @@ This module contains articles about core features in the Java language
 - [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)
 - [Java Default Parameters Using Method Overloading](https://www.baeldung.com/java-default-parameters-method-overloading)
+- [How to Return Multiple Values From a Java Method](https://www.baeldung.com/java-method-return-multiple-values)
+- [Guide to the Java finally Keyword](https://www.baeldung.com/java-finally-keyword)
 - [[<-- Prev]](/core-java-modules/core-java-lang)

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

@@ -9,3 +9,4 @@
 - [The strictfp Keyword in Java](https://www.baeldung.com/java-strictfp)
 - [Basic Calculator in Java](https://www.baeldung.com/java-basic-calculator)
 - [Overflow and Underflow in Java](https://www.baeldung.com/java-overflow-underflow)
+- [Obtaining a Power Set of a Set in Java](https://www.baeldung.com/java-power-set-of-a-set)

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

@@ -12,4 +12,5 @@ This module contains articles about Java syntax
 - [Variable Scope in Java](https://www.baeldung.com/java-variable-scope)
 - [Introduction to Basic Syntax in Java](https://www.baeldung.com/java-syntax)
 - [Java ‘protected’ Access Modifier](https://www.baeldung.com/java-protected-access-modifier)
+- [Using the Not Operator in If Conditions in Java](https://www.baeldung.com/java-using-not-in-if-conditions)
 - [[<-- Prev]](/core-java-modules/core-java-lang-syntax)

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

@@ -13,4 +13,7 @@ This module contains articles about Java syntax
 - [Infinite Loops in Java](https://www.baeldung.com/infinite-loops-java)
 - [Java Switch Statement](https://www.baeldung.com/java-switch)
 - [Breaking Out of Nested Loops](https://www.baeldung.com/java-breaking-out-nested-loop)
+- [Java Do-While Loop](https://www.baeldung.com/java-do-while-loop)
+- [Java While Loop](https://www.baeldung.com/java-while-loop)
+- [Java For Loop](https://www.baeldung.com/java-for-loop)
 - [[More -->]](/core-java-modules/core-java-lang-syntax-2)

core-java-modules/core-java-reflection/README.MD

@@ -6,4 +6,5 @@
 - [Guide to Java Reflection](http://www.baeldung.com/java-reflection)
 - [Call Methods at Runtime Using Java Reflection](http://www.baeldung.com/java-method-reflection)
 - [Changing Annotation Parameters At Runtime](http://www.baeldung.com/java-reflection-change-annotation-params)
-- [Dynamic Proxies in Java](http://www.baeldung.com/java-dynamic-proxies)
+- [Dynamic Proxies in Java](http://www.baeldung.com/java-dynamic-proxies)
+- [What Causes java.lang.reflect.InvocationTargetException?](https://www.baeldung.com/java-lang-reflect-invocationtargetexception)

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

@@ -0,0 +1,10 @@
+=========
+
+## Core Java 8 Cookbooks and Examples
+
+### Relevant Articles: 
+- [An Overview of Regular Expressions Performance in Java](https://www.baeldung.com/java-regex-performance)
+- [A Guide To Java Regular Expressions API](http://www.baeldung.com/regular-expressions-java)
+- [Guide to Escaping Characters in Java RegExps](http://www.baeldung.com/java-regexp-escape-char)
+- [Pre-compile Regex Patterns Into Pattern Objects](https://www.baeldung.com/java-regex-pre-compile)
+- [Difference Between Java Matcher find() and matches()](https://www.baeldung.com/java-matcher-find-vs-matches)

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

@@ -2,9 +2,9 @@
 <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-text</artifactId>
+    <artifactId>core-java-regex</artifactId>
     <version>0.1.0-SNAPSHOT</version>
-    <name>core-java-text</name>
+    <name>core-java-regex</name>
     <packaging>jar</packaging>
 
     <parent>
@@ -28,7 +28,7 @@
     </dependencies>
 
     <build>
-        <finalName>core-java-text</finalName>
+        <finalName>core-java-regex</finalName>
         <resources>
             <resource>
                 <directory>src/main/resources</directory>