Merge pull request #82 from eugenp/master

update

core-java-modules/core-java-10/README.md

@@ -5,7 +5,7 @@ This module contains articles about Java 10 core features
 ### Relevant Articles: 
 
 - [Java 10 LocalVariable Type-Inference](http://www.baeldung.com/java-10-local-variable-type-inference)
-- [Guide to Java 10](http://www.baeldung.com/java-10-overview)
+- [New Features in Java 10](https://www.baeldung.com/java-10-overview)
 - [Copy a List to Another List in Java](http://www.baeldung.com/java-copy-list-to-another)
 - [Deep Dive Into the New Java JIT Compiler – Graal](https://www.baeldung.com/graal-java-jit-compiler)
 - [Copying Sets in Java](https://www.baeldung.com/java-copy-sets)

core-java-modules/core-java-12/README.md

@@ -1,5 +1,4 @@
 ## Relevant Articles:
 
-
 - [String API Updates in Java 12](https://www.baeldung.com/java12-string-api)
-- [Java 12 New Features](https://www.baeldung.com/java-12-new-features)
+- [New Features in Java 12](https://www.baeldung.com/java-12-new-features)

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

@@ -1,4 +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)
+- [New Features in Java 13](https://www.baeldung.com/java-13-new-features)

core-java-modules/core-java-14/README.md

@@ -10,4 +10,4 @@ This module contains articles about Java 14.
 - [Helpful NullPointerExceptions in Java 14](https://www.baeldung.com/java-14-nullpointerexception)
 - [Foreign Memory Access API in Java 14](https://www.baeldung.com/java-foreign-memory-access)
 - [Java 14 Record Keyword](https://www.baeldung.com/java-record-keyword)
-- [Java 14 – New Features](https://www.baeldung.com/java-14-new-features)
+- [New Features in Java 14](https://www.baeldung.com/java-14-new-features)

core-java-modules/core-java-9-new-features/README.md

@@ -4,7 +4,7 @@ This module contains articles about core Java features that have been introduced
 
 ### Relevant Articles:
 
-- [Java 9 New Features](https://www.baeldung.com/new-java-9)
+- [New Features in Java 9](https://www.baeldung.com/new-java-9)
 - [Java 9 Variable Handles Demystified](http://www.baeldung.com/java-variable-handles)
 - [Exploring the New HTTP Client in Java 9 and 11](http://www.baeldung.com/java-9-http-client)
 - [Multi-Release Jar Files](https://www.baeldung.com/java-multi-release-jar)

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

@@ -3,4 +3,4 @@
 This module contains articles about Java Character Class
 
 ### Relevant Articles: 
-- [Character#isAlphabetic vs Character#isLetter](https://www.baeldung.com/java-character-isletter-isalphabetic)
+- [Character#isAlphabetic vs. Character#isLetter](https://www.baeldung.com/java-character-isletter-isalphabetic)

core-java-modules/core-java-collections-maps-2/src/main/java/com/baeldung/map/Product.java

@@ -26,7 +26,7 @@ public class Product {
         return tags;
     }
 
-    public Product addTagsOfOtherProdcut(Product product) {
+    public Product addTagsOfOtherProduct(Product product) {
         this.tags.addAll(product.getTags());
         return this;
     }
@@ -100,11 +100,11 @@ public class Product {
         HashMap<String, Product> productsByName = new HashMap<>();
         Product eBike2 = new Product("E-Bike", "A bike with a battery");
         eBike2.getTags().add("sport");
-        productsByName.merge("E-Bike", eBike2, Product::addTagsOfOtherProdcut);
+        productsByName.merge("E-Bike", eBike2, Product::addTagsOfOtherProduct);
 
         //Prior to Java 8:
         if(productsByName.containsKey("E-Bike")) {
-            productsByName.get("E-Bike").addTagsOfOtherProdcut(eBike2);
+            productsByName.get("E-Bike").addTagsOfOtherProduct(eBike2);
         } else {
             productsByName.put("E-Bike", eBike2);
         }
@@ -117,7 +117,7 @@ public class Product {
 
         productsByName.compute("E-Bike", (k,v) -> {
             if(v != null) {
-                return v.addTagsOfOtherProdcut(eBike2);
+                return v.addTagsOfOtherProduct(eBike2);
             } else {
                 return eBike2;
             }
@@ -125,7 +125,7 @@ public class Product {
 
         //Prior to Java 8:
         if(productsByName.containsKey("E-Bike")) {
-            productsByName.get("E-Bike").addTagsOfOtherProdcut(eBike2);
+            productsByName.get("E-Bike").addTagsOfOtherProduct(eBike2);
         } else {
             productsByName.put("E-Bike", eBike2);
         }

core-java-modules/core-java-collections-maps-3/pom.xml

@@ -20,6 +20,11 @@
             <artifactId>jmh-core</artifactId>
             <version>${jmh-core.version}</version>
         </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+        </dependency>
     </dependencies>
 
     <properties>

core-java-modules/core-java-collections-maps-3/src/main/java/com/baeldung/map/propertieshashmap/PropertiesToHashMapConverter.java

@@ -0,0 +1,39 @@
+package com.baeldung.map.propertieshashmap;
+
+import com.google.common.collect.Maps;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Properties;
+import java.util.stream.Collectors;
+
+public class PropertiesToHashMapConverter {
+
+    @SuppressWarnings({"rawtypes", "unchecked"})
+    public static HashMap<String, String> typeCastConvert(Properties prop) {
+        Map step1 = prop;
+        Map<String, String> step2 = (Map<String, String>) step1;
+        return new HashMap<>(step2);
+    }
+
+    public static HashMap<String, String> loopConvert(Properties prop) {
+        HashMap<String, String> retMap = new HashMap<>();
+        for (Map.Entry<Object, Object> entry : prop.entrySet()) {
+            retMap.put(String.valueOf(entry.getKey()), String.valueOf(entry.getValue()));
+        }
+        return retMap;
+    }
+
+    public static HashMap<String, String> streamConvert(Properties prop) {
+        return prop.entrySet().stream().collect(
+                Collectors.toMap(
+                  e -> String.valueOf(e.getKey()),
+                  e -> String.valueOf(e.getValue()),
+                  (prev, next) -> next, HashMap::new
+                ));
+    }
+
+    public static HashMap<String, String> guavaConvert(Properties prop) {
+        return Maps.newHashMap(Maps.fromProperties(prop));
+    }
+}

core-java-modules/core-java-collections-maps-3/src/test/java/com/baeldung/map/hashmap/loadfactor/HashMapLoadFactorUnitTest.java

@@ -0,0 +1,49 @@
+package com.baeldung.map.hashmap.loadfactor;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.Assert;
+import org.junit.jupiter.api.Test;
+
+public class HashMapLoadFactorUnitTest {
+
+    @Test
+    public void whenCreateMapWithDefaultParam_thenSucces() {
+        Map<String, String> mapWithDefaultParams = new HashMap<>();
+        mapWithDefaultParams.put("1", "one");
+        mapWithDefaultParams.put("2", "two");
+        mapWithDefaultParams.put("3", "three");
+        mapWithDefaultParams.put("4", "four");
+        mapWithDefaultParams.put("5", "five");
+        
+        Assert.assertEquals(5, mapWithDefaultParams.size());
+    }
+
+    @Test
+    public void whenCreateMapWithInitialCapacity_thenSucces() {
+        Map<String, String> mapWithInitialCapacity = new HashMap<>(5);
+        mapWithInitialCapacity.put("1", "one");
+        mapWithInitialCapacity.put("2", "two");
+        mapWithInitialCapacity.put("3", "three");
+        
+        Assert.assertEquals(3, mapWithInitialCapacity.size());
+    }
+
+    @Test
+    public void whenCreateMapWithInitialCapacityAndLF_thenSucces() {
+        Map<String, String> mapWithInitialCapacityAndLF = new HashMap<>(5, 0.5f);
+        mapWithInitialCapacityAndLF.put("1", "one");
+        mapWithInitialCapacityAndLF.put("2", "two");
+        mapWithInitialCapacityAndLF.put("3", "three");
+        mapWithInitialCapacityAndLF.put("4", "four");
+        mapWithInitialCapacityAndLF.put("5", "five");
+        mapWithInitialCapacityAndLF.put("6", "six");
+        mapWithInitialCapacityAndLF.put("7", "seven");
+        mapWithInitialCapacityAndLF.put("8", "eight");
+        mapWithInitialCapacityAndLF.put("9", "nine");
+        mapWithInitialCapacityAndLF.put("10", "ten");
+     
+        Assert.assertEquals(10, mapWithInitialCapacityAndLF.size());
+    }
+}

core-java-modules/core-java-collections-maps-3/src/test/java/com/baeldung/map/propertieshashmap/PropertiesToHashMapConverterUnitTest.java

@@ -0,0 +1,192 @@
+package com.baeldung.map.propertieshashmap;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.HashMap;
+import java.util.Properties;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class PropertiesToHashMapConverterUnitTest {
+
+    private Properties properties;
+
+    private final static String propertyFileName = "toHashMap.properties";
+
+    @BeforeEach
+    public void setup() throws IOException {
+        properties = new Properties();
+        try (InputStream is = getClass().getClassLoader().getResourceAsStream(propertyFileName)) {
+            if (is != null) {
+                properties.load(is);
+            }
+        }
+    }
+
+    @Test
+    public void havingPropertiesLoaded_whenCheck_thenEquals() {
+        assertEquals(3, properties.size());
+        assertEquals("str_value", properties.get("property1"));
+        assertEquals("123", properties.get("property2"));
+        assertEquals("", properties.get("property3"));
+    }
+
+    @Test
+    public void whenPropertiesModified_thenTypeSafeIssues() {
+        compromiseProperties(properties);
+
+        assertEquals(5, properties.size());
+
+        assertNull(properties.getProperty("property4"));
+        assertNotEquals(String.class, properties.get("property4").getClass());
+        assertEquals(456, properties.get("property4"));
+
+
+        assertNull(properties.getProperty("5"));
+        assertNotEquals(String.class, properties.get(5).getClass());
+        assertEquals(10.11, properties.get(5));
+    }
+
+    @Test
+    public void havingNonModifiedProperties_whenTypeCastConvert_thenNoTypeSafeIssues() {
+        HashMap<String, String> hMap = PropertiesToHashMapConverter.typeCastConvert(properties);
+
+        assertEquals(3, hMap.size());
+        assertEquals(String.class, hMap.get("property1").getClass());
+        assertEquals(properties.get("property1"), hMap.get("property1"));
+        assertEquals(String.class, hMap.get("property2").getClass());
+        assertEquals(properties.get("property2"), hMap.get("property2"));
+        assertEquals(String.class, hMap.get("property3").getClass());
+        assertEquals(properties.get("property3"), hMap.get("property3"));
+    }
+
+    @Test
+    public void havingModifiedProperties_whenTypeCastConvert_thenClassCastException() {
+        compromiseProperties(properties);
+        HashMap<String, String> hMap = PropertiesToHashMapConverter.typeCastConvert(properties);
+        assertEquals(5, hMap.size());
+
+        assertThrows(ClassCastException.class, () -> {
+            String s = hMap.get("property4");
+        });
+        assertEquals(Integer.class, ((Object) hMap.get("property4")).getClass());
+
+        assertNull(hMap.get("5"));
+        assertNotNull(hMap.get(5));
+        assertThrows(ClassCastException.class, () -> {
+            String s = hMap.get(5);
+        });
+        assertEquals(Double.class, ((Object) hMap.get(5)).getClass());
+    }
+
+    @Test
+    public void havingNonModifiedProperties_whenLoopConvert_thenNoTypeSafeIssues() {
+        HashMap<String, String> hMap = PropertiesToHashMapConverter.loopConvert(properties);
+
+        assertEquals(3, hMap.size());
+        assertEquals(String.class, hMap.get("property1").getClass());
+        assertEquals(properties.get("property1"), hMap.get("property1"));
+        assertEquals(String.class, hMap.get("property2").getClass());
+        assertEquals(properties.get("property2"), hMap.get("property2"));
+        assertEquals(String.class, hMap.get("property3").getClass());
+        assertEquals(properties.get("property3"), hMap.get("property3"));
+    }
+
+    @Test
+    public void havingModifiedProperties_whenLoopConvert_thenNoClassCastException() {
+        compromiseProperties(properties);
+        HashMap<String, String> hMap = PropertiesToHashMapConverter.loopConvert(properties);
+        assertEquals(5, hMap.size());
+
+        assertDoesNotThrow(() -> {
+            String s = hMap.get("property4");
+        });
+        assertEquals(String.class, hMap.get("property4").getClass());
+        assertEquals("456", hMap.get("property4"));
+
+        assertDoesNotThrow(() -> {
+            String s = hMap.get("5");
+        });
+        assertEquals("10.11", hMap.get("5"));
+    }
+
+    @Test
+    public void havingNonModifiedProperties_whenStreamConvert_thenNoTypeSafeIssues() {
+        HashMap<String, String> hMap = PropertiesToHashMapConverter.streamConvert(properties);
+
+        assertEquals(3, hMap.size());
+        assertEquals(String.class, hMap.get("property1").getClass());
+        assertEquals(properties.get("property1"), hMap.get("property1"));
+        assertEquals(String.class, hMap.get("property2").getClass());
+        assertEquals(properties.get("property2"), hMap.get("property2"));
+        assertEquals(String.class, hMap.get("property3").getClass());
+        assertEquals(properties.get("property3"), hMap.get("property3"));
+    }
+
+    @Test
+    public void havingModifiedProperties_whenStreamConvert_thenNoClassCastException() {
+        compromiseProperties(properties);
+        HashMap<String, String> hMap = PropertiesToHashMapConverter.streamConvert(properties);
+        assertEquals(5, hMap.size());
+
+        assertDoesNotThrow(() -> {
+            String s = hMap.get("property4");
+        });
+        assertEquals(String.class, hMap.get("property4").getClass());
+        assertEquals("456", hMap.get("property4"));
+
+        assertDoesNotThrow(() -> {
+            String s = hMap.get("5");
+        });
+        assertEquals("10.11", hMap.get("5"));
+    }
+
+    @Test
+    public void havingModifiedProperties_whenLoopConvertAndStreamConvert_thenHashMapsSame() {
+        compromiseProperties(properties);
+        HashMap<String, String> hMap1 = PropertiesToHashMapConverter.loopConvert(properties);
+        HashMap<String, String> hMap2 = PropertiesToHashMapConverter.streamConvert(properties);
+
+        assertEquals(hMap2, hMap1);
+    }
+
+    @Test
+    public void havingNonModifiedProperties_whenGuavaConvert_thenNoTypeSafeIssues() {
+        HashMap<String, String> hMap = PropertiesToHashMapConverter.guavaConvert(properties);
+
+        assertEquals(3, hMap.size());
+        assertEquals(String.class, hMap.get("property1").getClass());
+        assertEquals(properties.get("property1"), hMap.get("property1"));
+        assertEquals(String.class, hMap.get("property2").getClass());
+        assertEquals(properties.get("property2"), hMap.get("property2"));
+        assertEquals(String.class, hMap.get("property3").getClass());
+        assertEquals(properties.get("property3"), hMap.get("property3"));
+    }
+
+    @Test
+    public void havingModifiedProperties_whenGuavaConvert_thenUnableToConvertAndThrowException() {
+        compromiseProperties(properties);
+        assertThrows(Exception.class, () -> PropertiesToHashMapConverter.guavaConvert(properties));
+    }
+
+    @Test
+    public void havingModifiedPropertiesWithNoIntegerValue_whenGuavaConvert_thenNullPointerException() {
+        properties.put("property4", 456);
+        assertThrows(NullPointerException.class, () -> PropertiesToHashMapConverter.guavaConvert(properties));
+    }
+
+    @Test
+    public void havingModifiedPropertiesWithNoIntegerKey_whenGuavaConvert_thenClassCastException() {
+        properties.put(5, 10.11);
+        assertThrows(ClassCastException.class, () -> PropertiesToHashMapConverter.guavaConvert(properties));
+    }
+
+
+    private void compromiseProperties(Properties prop) {
+        prop.put("property4", 456);
+        prop.put(5, 10.11);
+    }
+}

core-java-modules/core-java-collections-maps-3/src/test/resources/toHashMap.properties

@@ -0,0 +1,3 @@
+property1=str_value
+property2=123
+property3=

core-java-modules/core-java-concurrency-advanced-4/README.md

@@ -1,3 +1,4 @@
 ### Relevant Articles:
 
 - [Binary Semaphore vs Reentrant Lock](https://www.baeldung.com/java-binary-semaphore-vs-reentrant-lock)
+- [Bad Practices With Synchronization](https://www.baeldung.com/java-synchronization-bad-practices)

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

@@ -11,4 +11,5 @@ This module contains articles about working with the Java Virtual Machine (JVM).
 - [Where Is the Array Length Stored in JVM?](https://www.baeldung.com/java-jvm-array-length)
 - [Memory Address of Objects in Java](https://www.baeldung.com/java-object-memory-address)
 - [List All Classes Loaded in a Specific Class Loader](https://www.baeldung.com/java-list-classes-class-loader)
+- [An Introduction to the Constant Pool in the JVM](https://www.baeldung.com/jvm-constant-pool)
 - More articles: [[<-- prev]](/core-java-modules/core-java-jvm)

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

@@ -11,4 +11,5 @@ This module contains articles about core features in the Java language
 - [The transient Keyword in Java](https://www.baeldung.com/java-transient-keyword)
 - [How to Access an Iteration Counter in a For Each Loop](https://www.baeldung.com/java-foreach-counter)
 - [Comparing Doubles in Java](https://www.baeldung.com/java-comparing-doubles)
+- [Guide to Implementing the compareTo Method](https://www.baeldung.com/java-compareto)
 - [[<-- Prev]](/core-java-modules/core-java-lang-2)

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/compareto/BankAccount.java

@@ -0,0 +1,16 @@
+package com.baeldung.compareto;
+
+public class BankAccount implements Comparable<BankAccount> {
+
+    private final int balance;
+
+    public BankAccount(int balance) {
+        this.balance = balance;
+    }
+
+    @Override
+    public int compareTo(BankAccount anotherAccount) {
+        return this.balance - anotherAccount.balance;
+    }
+
+}

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/compareto/BankAccountFix.java

@@ -0,0 +1,16 @@
+package com.baeldung.compareto;
+
+public class BankAccountFix implements Comparable<BankAccountFix> {
+
+    private final int balance;
+
+    public BankAccountFix(int balance) {
+        this.balance = balance;
+    }
+
+    @Override
+    public int compareTo(BankAccountFix anotherAccount) {
+        return Integer.compare(this.balance, anotherAccount.balance);
+    }
+
+}

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/compareto/FootballPlayer.java

@@ -0,0 +1,32 @@
+package com.baeldung.compareto;
+
+public class FootballPlayer implements Comparable<FootballPlayer> {
+
+    private final String name;
+    private final int goalsScored;
+
+    public FootballPlayer(String name, int goalsScored) {
+        this.name = name;
+        this.goalsScored = goalsScored;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    @Override
+    public int compareTo(FootballPlayer anotherPlayer) {
+        return Integer.compare(this.goalsScored, anotherPlayer.goalsScored);
+    }
+
+    @Override
+    public boolean equals(Object object) {
+        if (this == object)
+            return true;
+        if (object == null || getClass() != object.getClass())
+            return false;
+        FootballPlayer player = (FootballPlayer) object;
+        return name.equals(player.name);
+    }
+
+}

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/compareto/HandballPlayer.java

@@ -0,0 +1,12 @@
+package com.baeldung.compareto;
+
+public class HandballPlayer {
+
+    private final String name;
+    private final int height;
+
+    public HandballPlayer(String name, int height) {
+        this.name = name;
+        this.height = height;
+    }
+}

core-java-modules/core-java-lang-3/src/test/java/com/baeldung/compareto/ArraysSortingUnitTest.java

@@ -0,0 +1,25 @@
+package com.baeldung.compareto;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ArraysSortingUnitTest {
+
+    @Test
+    public void givenArrayOfNumbers_whenSortingArray_thenNumbersAreSortedAscending() {
+        int[] numbers = new int[] {5, 3, 9, 11, 1, 7};
+        Arrays.sort(numbers);
+        assertThat(numbers).containsExactly(1, 3, 5, 7, 9, 11);
+    }
+
+    @Test
+    public void givenArrayOfStrings_whenSortingArray_thenStringsAreSortedAlphabetically() {
+        String[] players = new String[] {"ronaldo",  "modric", "ramos", "messi"};
+        Arrays.sort(players);
+        assertThat(players).containsExactly("messi", "modric", "ramos", "ronaldo");
+    }
+
+}

core-java-modules/core-java-lang-3/src/test/java/com/baeldung/compareto/BankAccountFixUnitTest.java

@@ -0,0 +1,25 @@
+package com.baeldung.compareto;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class BankAccountFixUnitTest {
+
+    @Test
+    public void givenComparisonBasedImpl_whenUsingSmallIntegers_thenComparisonWorks() {
+        BankAccountFix accountOne = new BankAccountFix(5000);
+        BankAccountFix accountTwo = new BankAccountFix(1000);
+        int comparison = accountOne.compareTo(accountTwo);
+        assertThat(comparison).isPositive();
+    }
+
+    @Test
+    public void givenComparisonBasedImpl_whenUsingLargeIntegers_thenComparisonWorks() {
+        BankAccountFix accountOne = new BankAccountFix(1900000000);
+        BankAccountFix accountTwo = new BankAccountFix(-2000000000);
+        int comparison = accountOne.compareTo(accountTwo);
+        assertThat(comparison).isPositive();
+    }
+
+}

core-java-modules/core-java-lang-3/src/test/java/com/baeldung/compareto/BankAccountUnitTest.java

@@ -0,0 +1,25 @@
+package com.baeldung.compareto;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.*;
+
+public class BankAccountUnitTest {
+
+    @Test
+    public void givenSubtractionBasedImpl_whenUsingSmallIntegers_thenComparisonWorks() {
+        BankAccount accountOne = new BankAccount(5000);
+        BankAccount accountTwo = new BankAccount(1000);
+        int comparison = accountOne.compareTo(accountTwo);
+        assertThat(comparison).isPositive();
+    }
+
+    @Test
+    public void givenSubtractionBasedImpl_whenUsingLargeIntegers_thenComparisonBreaks() {
+        BankAccount accountOne = new BankAccount(1900000000);
+        BankAccount accountTwo = new BankAccount(-2000000000);
+        int comparison = accountOne.compareTo(accountTwo);
+        assertThat(comparison).isNegative();
+    }
+
+}

core-java-modules/core-java-lang-3/src/test/java/com/baeldung/compareto/FootballPlayerUnitTest.java

@@ -0,0 +1,57 @@
+package com.baeldung.compareto;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.TreeSet;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class FootballPlayerUnitTest {
+
+    @Test
+    public void givenInconsistentCompareToAndEqualsImpl_whenUsingSortedSet_thenSomeElementsAreNotAdded() {
+        FootballPlayer messi = new FootballPlayer("Messi", 800);
+        FootballPlayer ronaldo = new FootballPlayer("Ronaldo", 800);
+
+        TreeSet<FootballPlayer> set = new TreeSet<>();
+        set.add(messi);
+        set.add(ronaldo);
+
+        assertThat(set).hasSize(1);
+        assertThat(set).doesNotContain(ronaldo);
+    }
+
+    @Test
+    public void givenCompareToImpl_whenUsingCustomComparator_thenComparatorLogicIsApplied() {
+        FootballPlayer ronaldo = new FootballPlayer("Ronaldo", 900);
+        FootballPlayer messi = new FootballPlayer("Messi", 800);
+        FootballPlayer modric = new FootballPlayer("Modric", 100);
+
+        List<FootballPlayer> players = Arrays.asList(ronaldo, messi, modric);
+        Comparator<FootballPlayer> nameComparator = Comparator.comparing(FootballPlayer::getName);
+        Collections.sort(players, nameComparator);
+
+        assertThat(players).containsExactly(messi, modric, ronaldo);
+    }
+
+    @Test
+    public void givenCompareToImpl_whenSavingElementsInTreeMap_thenKeysAreSortedUsingCompareTo() {
+        FootballPlayer ronaldo = new FootballPlayer("Ronaldo", 900);
+        FootballPlayer messi = new FootballPlayer("Messi", 800);
+        FootballPlayer modric = new FootballPlayer("Modric", 100);
+
+        Map<FootballPlayer, String> players = new TreeMap<>();
+        players.put(ronaldo, "forward");
+        players.put(messi, "forward");
+        players.put(modric, "midfielder");
+
+        assertThat(players.keySet()).containsExactly(modric, messi, ronaldo);
+    }
+
+}

core-java-modules/core-java-lang-3/src/test/java/com/baeldung/compareto/HandballPlayerUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.compareto;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+
+public class HandballPlayerUnitTest {
+
+    @Test
+    public void givenComparableIsNotImplemented_whenSortingArray_thenExceptionIsThrown() {
+        HandballPlayer duvnjak = new HandballPlayer("Duvnjak", 197);
+        HandballPlayer hansen = new HandballPlayer("Hansen", 196);
+
+        HandballPlayer[] players = new HandballPlayer[] {duvnjak, hansen};
+
+        assertThatExceptionOfType(ClassCastException.class).isThrownBy(() -> Arrays.sort(players));
+    }
+
+}

core-java-modules/core-java-lang-math-3/README.md

@@ -4,6 +4,5 @@
 
 ### Relevant articles:
 
-- [Calculate Factorial in Java](https://www.baeldung.com/java-calculate-factorial)
 - [Evaluating a Math Expression in Java](https://www.baeldung.com/java-evaluate-math-expression-string)
 - More articles: [[<-- Prev]](/core-java-modules/core-java-lang-math-2)

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

@@ -7,3 +7,4 @@ This module contains articles about generics in Java
 - [Type Erasure in Java Explained](https://www.baeldung.com/java-type-erasure)
 - [Raw Types in Java](https://www.baeldung.com/raw-types-java)
 - [Super Type Tokens in Java Generics](https://www.baeldung.com/java-super-type-tokens)
+- [Java Warning “unchecked conversion”](https://www.baeldung.com/java-unchecked-conversion)

core-java-modules/core-java-reflection-2/src/main/java/com/baeldung/reflection/check/abstractclass/InterfaceExample.java

@@ -0,0 +1,4 @@
+package com.baeldung.reflection.check.abstractclass;
+
+public interface InterfaceExample {
+}

core-java-modules/core-java-reflection-2/src/test/java/com/baeldung/reflection/check/abstractclass/AbstractExampleUnitTest.java

@@ -1,16 +1,36 @@
 package com.baeldung.reflection.check.abstractclass;
 
-import java.lang.reflect.Modifier;
-
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
+import java.lang.reflect.Modifier;
+import java.util.Date;
+
 class AbstractExampleUnitTest {
 
     @Test
-    void givenAbstractClass_whenCheckModifierIsAbstract_thenTrue() throws Exception {
+    void givenAbstractClass_whenCheckModifierIsAbstract_thenTrue() {
         Class<AbstractExample> clazz = AbstractExample.class;
         Assertions.assertTrue(Modifier.isAbstract(clazz.getModifiers()));
     }
 
+    @Test
+    void givenInterface_whenCheckModifierIsAbstract_thenTrue() {
+        Class<InterfaceExample> clazz = InterfaceExample.class;
+        Assertions.assertTrue(Modifier.isAbstract(clazz.getModifiers()));
+    }
+
+    @Test
+    void givenAbstractClass_whenCheckIsAbstractClass_thenTrue() {
+        Class<AbstractExample> clazz = AbstractExample.class;
+        int mod = clazz.getModifiers();
+        Assertions.assertTrue(Modifier.isAbstract(mod) && !Modifier.isInterface(mod));
+    }
+
+    @Test
+    void givenConcreteClass_whenCheckIsAbstractClass_thenFalse() {
+        Class<Date> clazz = Date.class;
+        int mod = clazz.getModifiers();
+        Assertions.assertFalse(Modifier.isAbstract(mod) && !Modifier.isInterface(mod));
+    }
 }

core-java-modules/core-java-security-2/src/main/java/com/baeldung/egd/JavaSecurityEgdTester.java

@@ -0,0 +1,23 @@
+package com.baeldung.egd;
+
+import java.security.SecureRandom;
+
+/**
+ * JavaSecurityEgdTester - run this with JVM parameter java.security.egd, e.g.:
+ *     java -Djava.security.egd=file:/dev/urandom -cp . com.baeldung.egd.JavaSecurityEgdTester
+ */
+public class JavaSecurityEgdTester {
+    public static final double NANOSECS = 1000000000.0;
+    public static final String JAVA_SECURITY_EGD = "java.security.egd";
+
+    public static void main(String[] args) {
+        SecureRandom secureRandom = new SecureRandom();
+        long start = System.nanoTime();
+        byte[] randomBytes = new byte[256];
+        secureRandom.nextBytes(randomBytes);
+        double duration = (System.nanoTime() - start) / NANOSECS;
+
+        String message = String.format("java.security.egd=%s took %.3f seconds and used the %s algorithm", System.getProperty(JAVA_SECURITY_EGD), duration, secureRandom.getAlgorithm());
+        System.out.println(message);
+    }
+}

guest/core-kotlin/README.md

@@ -1,3 +1,3 @@
 ### Relevant Articles:
 
-- [Kotlin vs Java](https://www.baeldung.com/kotlin/kotlin-vs-java)
+- [Kotlin vs Java](https://www.baeldung.com/kotlin/vs-java)