resolved

core-java-8/src/main/java/com/baeldung/hashtable/Word.java

@@ -0,0 +1,28 @@
+package com.baeldung.hashtable;
+
+public class Word {
+    private String name;
+
+    public Word(String name) {
+        this.name = name;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public boolean equals(Object o) {
+        if (o == this)
+            return true;
+        if (!(o instanceof Word))
+            return false;
+
+        Word word = (Word) o;
+        return word.getName().equals(this.name) ? true : false;
+
+    }
+
+    public int hashCode() {
+        return name.hashCode();
+    }
+}

core-java-8/src/main/java/com/baeldung/optional/OrElseAndOrElseGet.java

@@ -0,0 +1,34 @@
+package com.baeldung.optional;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Optional;
+import java.util.Random;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class OrElseAndOrElseGet {
+
+    public static List<String> names = Arrays.asList("John", "Jones", "Kelly", "Cristina", "Raven");
+
+    private static final Logger LOG = LoggerFactory.getLogger(OrElseAndOrElseGet.class);
+
+    public String getRandomName() {
+        LOG.info("getRandomName() method - start");
+        Random random = new Random();
+        int index = random.nextInt(5);
+        LOG.info("getRandomName() method - end");
+        return names.get(index);
+    }
+
+    public String getNameUsingOrElse(String name) {
+        return Optional.ofNullable(name)
+            .orElse(getRandomName());
+    }
+
+    public String getNameUsingOrElseGet(String name) {
+        return Optional.ofNullable(name)
+            .orElseGet(() -> getRandomName());
+    }
+}

core-java-8/src/main/java/com/baeldung/optional/OrElseAndOrElseGetBenchmarkRunner.java

@@ -0,0 +1,37 @@
+package com.baeldung.optional;
+
+import java.io.IOException;
+import java.util.concurrent.TimeUnit;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.runner.RunnerException;
+
+@Fork(1)
+@State(Scope.Benchmark)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+public class OrElseAndOrElseGetBenchmarkRunner {
+
+    private OrElseAndOrElseGet orElsevsOrElseGet = new OrElseAndOrElseGet();
+
+    public static void main(String[] args) throws RunnerException, IOException {
+        org.openjdk.jmh.Main.main(args);
+    }
+
+    @Benchmark
+    public String orElseBenchmark() {
+        return orElsevsOrElseGet.getNameUsingOrElse("baeldung");
+    }
+
+    @Benchmark
+    public String orElseGetBenchmark() {
+        return orElsevsOrElseGet.getNameUsingOrElseGet("baeldung");
+    }
+
+}

core-java-8/src/test/java/com/baeldung/hashtable/HashtableUnitTest.java

@@ -0,0 +1,274 @@
+package com.baeldung.hashtable;
+
+import java.util.ConcurrentModificationException;
+import java.util.Enumeration;
+import java.util.Hashtable;
+import java.util.Iterator;
+import java.util.Map;
+
+import static org.junit.Assert.*;
+import static org.hamcrest.Matchers.*;
+import org.junit.Test;
+
+public class HashtableUnitTest {
+
+    @Test
+    public void whenPutAndGet_thenReturnsValue() {
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+
+        Word word = new Word("cat");
+        table.put(word, "an animal");
+
+        String definition = table.get(word);
+
+        assertEquals("an animal", definition);
+
+        definition = table.remove(word);
+
+        assertEquals("an animal", definition);
+    }
+
+    @Test
+    public void whenThesameInstanceOfKey_thenReturnsValue() {
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        Word word = new Word("cat");
+        table.put(word, "an animal");
+        String extracted = table.get(word);
+        assertEquals("an animal", extracted);
+    }
+
+    @Test
+    public void whenEqualsOverridden_thenReturnsValue() {
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        Word word = new Word("cat");
+        table.put(word, "an animal");
+        String extracted = table.get(new Word("cat"));
+        assertEquals("an animal", extracted);
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void whenNullKey_thenException() {
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        table.put(null, "an animal");
+    }
+
+    @Test(expected = ConcurrentModificationException.class)
+    public void whenIterate_thenFailFast() {
+
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        table.put(new Word("cat"), "an animal");
+        table.put(new Word("dog"), "another animal");
+
+        Iterator<Word> it = table.keySet().iterator();
+        System.out.println("iterator created");
+
+        table.remove(new Word("dog"));
+        System.out.println("element removed");
+
+        while (it.hasNext()) {
+            Word key = it.next();
+            System.out.println(table.get(key));
+        }
+    }
+
+    @Test
+    public void whenEnumerate_thenNotFailFast() {
+
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        table.put(new Word("1"), "one");
+        table.put(new Word("2"), "two");
+        table.put(new Word("3"), "three");
+        table.put(new Word("4"), "four");
+        table.put(new Word("5"), "five");
+        table.put(new Word("6"), "six");
+        table.put(new Word("7"), "seven");
+        table.put(new Word("8"), "eight");
+
+        Enumeration<Word> enumKey = table.keys();
+        System.out.println("Enumeration created");
+        table.remove(new Word("1"));
+        System.out.println("element removed");
+        while (enumKey.hasMoreElements()) {
+            Word key = enumKey.nextElement();
+            System.out.println(table.get(key));
+        }
+    }
+
+    @Test
+    public void whenAddElements_thenIterationOrderUnpredicable() {
+
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        table.put(new Word("1"), "one");
+        table.put(new Word("2"), "two");
+        table.put(new Word("3"), "three");
+        table.put(new Word("4"), "four");
+        table.put(new Word("5"), "five");
+        table.put(new Word("6"), "six");
+        table.put(new Word("7"), "seven");
+        table.put(new Word("8"), "eight");
+
+        Iterator<Map.Entry<Word, String>> it = table.entrySet().iterator();
+        while (it.hasNext()) {
+            Map.Entry<Word, String> entry = it.next();
+            System.out.println(entry.getValue());
+        }
+    }
+
+    @Test
+    public void whenGetOrDefault_thenDefaultGot() {
+
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        table.put(new Word("cat"), "a small domesticated carnivorous mammal");
+        Word key = new Word("dog");
+        String definition;
+
+        // old way
+        /* if (table.containsKey(key)) {
+            definition = table.get(key);
+        } else {
+            definition = "not found";
+        }*/
+
+        // new way
+        definition = table.getOrDefault(key, "not found");
+
+        assertThat(definition, is("not found"));
+    }
+
+    @Test
+    public void whenPutifAbsent_thenNotRewritten() {
+
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        table.put(new Word("cat"), "a small domesticated carnivorous mammal");
+
+        String definition = "an animal";
+        // old way
+        /* if (!table.containsKey(new Word("cat"))) {
+            table.put(new Word("cat"), definition);
+        }*/
+        // new way
+        table.putIfAbsent(new Word("cat"), definition);
+
+        assertThat(table.get(new Word("cat")), is("a small domesticated carnivorous mammal"));
+    }
+
+    @Test
+    public void whenRemovePair_thenCheckKeyAndValue() {
+
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        table.put(new Word("cat"), "a small domesticated carnivorous mammal");
+
+        // old way
+        /* if (table.get(new Word("cat")).equals("an animal")) {
+            table.remove(new Word("cat"));
+        }*/
+
+        // new way
+        boolean result = table.remove(new Word("cat"), "an animal");
+
+        assertThat(result, is(false));
+    }
+
+    @Test
+    public void whenReplacePair_thenValueChecked() {
+
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        table.put(new Word("cat"), "a small domesticated carnivorous mammal");
+
+        String definition = "an animal";
+
+        // old way
+        /* if (table.containsKey(new Word("cat")) && table.get(new Word("cat")).equals("a small domesticated carnivorous mammal")) {
+            table.put(new Word("cat"), definition);
+        }*/
+        // new way
+        table.replace(new Word("cat"), "a small domesticated carnivorous mammal", definition);
+
+        assertThat(table.get(new Word("cat")), is("an animal"));
+
+    }
+
+    @Test
+    public void whenKeyIsAbsent_thenNotRewritten() {
+
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        table.put(new Word("cat"), "a small domesticated carnivorous mammal");
+
+        // old way
+        /* if (!table.containsKey(cat)) {
+            String definition = "an animal";// calculate
+            table.put(new Word("cat"), definition);
+        }
+        */
+        // new way
+
+        table.computeIfAbsent(new Word("cat"), key -> "an animal");
+        assertThat(table.get(new Word("cat")), is("a small domesticated carnivorous mammal"));
+
+    }
+
+    @Test
+    public void whenKeyIsPresent_thenComputeIfPresent() {
+
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        table.put(new Word("cat"), "a small domesticated carnivorous mammal");
+
+        Word cat = new Word("cat");
+        // old way
+        /* if (table.containsKey(cat)) {
+            String concatination = cat.getName() + " - " + table.get(cat);
+            table.put(cat, concatination);
+        }*/
+
+        // new way
+        table.computeIfPresent(cat, (key, value) -> key.getName() + " - " + value);
+
+        assertThat(table.get(cat), is("cat - a small domesticated carnivorous mammal"));
+
+    }
+
+    @Test
+    public void whenCompute_thenForAllKeys() {
+
+        Hashtable<String, Integer> table = new Hashtable<String, Integer>();
+        String[] animals = { "cat", "dog", "dog", "cat", "bird", "mouse", "mouse" };
+        for (String animal : animals) {
+            table.compute(animal, (key, value) -> (value == null ? Integer.valueOf(1) : Integer.valueOf(value) + 1));
+        }
+        assertThat(table.values(), hasItems(2, 2, 2, 1));
+
+    }
+
+    @Test
+    public void whenInsteadOfCompute_thenMerge() {
+
+        Hashtable<String, Integer> table = new Hashtable<String, Integer>();
+        String[] animals = { "cat", "dog", "dog", "cat", "bird", "mouse", "mouse" };
+        for (String animal : animals) {
+            table.merge(animal, 1, (oldValue, value) -> (oldValue + value));
+        }
+        assertThat(table.values(), hasItems(2, 2, 2, 1));
+    }
+
+    @Test
+    public void whenForeach_thenIterate() {
+
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        table.put(new Word("cat"), "a small domesticated carnivorous mammal");
+        table.put(new Word("dog"), "another animal");
+        table.forEach((k, v) -> System.out.println(k.getName() + " - " + v)
+
+        );
+    }
+
+    @Test
+    public void whenReplaceall_thenNoIterationNeeded() {
+
+        Hashtable<Word, String> table = new Hashtable<Word, String>();
+        table.put(new Word("cat"), "a small domesticated carnivorous mammal");
+        table.put(new Word("dog"), "another animal");
+        table.replaceAll((k, v) -> k.getName() + " - " + v);
+
+        assertThat(table.values(), hasItems("cat - a small domesticated carnivorous mammal", "dog - another animal"));
+    }
+}

core-java-8/src/test/java/com/baeldung/java8/optional/OrElseAndOrElseGetTest.java

@@ -0,0 +1,44 @@
+package com.baeldung.java8.optional;
+
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import static org.junit.Assert.*;
+
+import com.baeldung.optional.OrElseAndOrElseGet;
+
+public class OrElseAndOrElseGetTest {
+
+    private OrElseAndOrElseGet orElsevsOrElseGet = new OrElseAndOrElseGet();
+
+    private static final Logger LOG = LoggerFactory.getLogger(OrElseAndOrElseGetTest.class);
+
+    @Test
+    public void givenNonEmptyOptional_whenOrElseUsed_thenGivenStringReturned() {
+        LOG.info("In givenNonEmptyOptional_whenOrElseUsed_thenGivenStringReturned()");
+        String name = orElsevsOrElseGet.getNameUsingOrElse("baeldung");
+        assertEquals(name, "baeldung");
+    }
+
+    @Test
+    public void givenEmptyOptional_whenOrElseUsed_thenRandomStringReturned() {
+        LOG.info("In givenEmptyOptional_whenOrElseUsed_thenRandomStringReturned()");
+        String name = orElsevsOrElseGet.getNameUsingOrElse(null);
+        assertTrue(orElsevsOrElseGet.names.contains(name));
+    }
+
+    @Test
+    public void givenNonEmptyOptional_whenOrElseGetUsed_thenGivenStringReturned() {
+        LOG.info("In givenNonEmptyOptional_whenOrElseGetUsed_thenGivenStringReturned()");
+        String name = orElsevsOrElseGet.getNameUsingOrElseGet("baeldung");
+        assertEquals(name, "baeldung");
+    }
+
+    @Test
+    public void givenEmptyOptional_whenOrElseGetUsed_thenRandomStringReturned() {
+        LOG.info("In givenEmptyOptional_whenOrElseGetUsed_thenRandomStringReturned()");
+        String name = orElsevsOrElseGet.getNameUsingOrElseGet(null);
+        assertTrue(orElsevsOrElseGet.names.contains(name));
+    }
+}

core-java/README.md

@@ -74,17 +74,14 @@
 - [CharSequence vs. String in Java](http://www.baeldung.com/java-char-sequence-string)
 - [Period and Duration in Java](http://www.baeldung.com/java-period-duration)
 - [Guide to the Diamond Operator in Java](http://www.baeldung.com/java-diamond-operator)
-- [Singletons in Java](http://www.baeldung.com/java-singleton)
 - [“Sneaky Throws” in Java](http://www.baeldung.com/java-sneaky-throws)
 - [OutOfMemoryError: GC Overhead Limit Exceeded](http://www.baeldung.com/java-gc-overhead-limit-exceeded)
 - [StringBuilder and StringBuffer in Java](http://www.baeldung.com/java-string-builder-string-buffer)
 - [Number of Digits in an Integer in Java](http://www.baeldung.com/java-number-of-digits-in-int)
-- [Proxy, Decorator, Adapter and Bridge Patterns](http://www.baeldung.com/java-structural-design-patterns)
 - [Creating a Java Compiler Plugin](http://www.baeldung.com/java-build-compiler-plugin)
 - [A Guide to the Static Keyword in Java](http://www.baeldung.com/java-static)
 - [Initializing Arrays in Java](http://www.baeldung.com/java-initialize-array)
 - [Guide to Java String Pool](http://www.baeldung.com/java-string-pool)
-- [Introduction to Creational Design Patterns](http://www.baeldung.com/creational-design-patterns)
 - [Quick Example - Comparator vs Comparable in Java](http://www.baeldung.com/java-comparator-comparable)
 - [Quick Guide to Java Stack](http://www.baeldung.com/java-stack)
 - [The Java continue and break Keywords](http://www.baeldung.com/java-continue-and-break)
@@ -116,8 +113,6 @@
 - [Comparing Strings in Java](http://www.baeldung.com/java-compare-strings)
 - [Guide to Inheritance in Java](http://www.baeldung.com/java-inheritance)
 - [Guide to Externalizable Interface in Java](http://www.baeldung.com/java-externalizable)
-- [The Observer Pattern in Java](http://www.baeldung.com/java-observer-pattern)
-- [Flyweight Pattern in Java](http://www.baeldung.com/java-flyweight)
 - [Object Type Casting in Java](http://www.baeldung.com/java-type-casting)
 - [A Practical Guide to DecimalFormat](http://www.baeldung.com/java-decimalformat)
 - [How to Detect the OS Using Java](http://www.baeldung.com/java-detect-os)
@@ -136,7 +131,6 @@
 - [Class Loaders in Java](http://www.baeldung.com/java-classloaders)
 - [Find Sum and Average in a Java Array](http://www.baeldung.com/java-array-sum-average)
 - [Java List UnsupportedOperationException](http://www.baeldung.com/java-list-unsupported-operation-exception)
-- [Service Locator Pattern](http://www.baeldung.com/java-service-locator-pattern)
 - [Type Erasure in Java Explained](http://www.baeldung.com/java-type-erasure)
 - [BigDecimal and BigInteger in Java](http://www.baeldung.com/java-bigdecimal-biginteger)
 - [Display All Time Zones With GMT And UTC in Java](http://www.baeldung.com/java-time-zones)
@@ -145,4 +139,5 @@
 - [Sending Emails with Java](http://www.baeldung.com/java-email)
 - [Introduction to SSL in Java](http://www.baeldung.com/java-ssl)
 - [Java KeyStore API](http://www.baeldung.com/java-keystore)
-- [Double-Checked Locking with Singleton](http://www.baeldung.com/java-singleton-double-checked-locking)
+- [Using Java Assertions](http://www.baeldung.com/java-assert)
+- [Guide to Java Clock Class](http://www.baeldung.com/java-clock)

core-java/src/main/java/com/baeldung/designpatterns/creational/abstractfactory/Color.java

@@ -1,5 +0,0 @@
-package com.baeldung.designpatterns.creational.abstractfactory;
-
-public interface Color {
-    String getColor();
-}

core-java/src/main/java/com/baeldung/designpatterns/creational/factory/Polygon.java

@@ -1,5 +0,0 @@
-package com.baeldung.designpatterns.creational.factory;
-
-public interface Polygon {
-    String getType();
-}

core-java/src/main/java/com/baeldung/nan/NaNExample.java

@@ -0,0 +1,81 @@
+package com.baeldung.nan;
+
+/**
+ * Sample usage of NaN.
+ *
+ */
+public class NaNExample {
+
+    public static void main(String[] args) {
+        NaNExample naNExample = new NaNExample();
+        naNExample.demo();
+    }
+
+    void demo() {
+        undefined_operations_produce_NaN();
+        operations_with_no_real_results_produce_NaN();
+        operations_with_NaN_produce_NaN();
+        comparison_with_NaN();
+        check_if_a_value_is_NaN();
+        assign_NaN_to_missing_values();
+    }
+
+    void undefined_operations_produce_NaN() {
+        System.out.println("Undefined Operations Produce NaN");
+        final double ZERO = 0;
+        System.out.println("ZERO / ZERO = " + (ZERO / ZERO));
+        System.out.println("INFINITY - INFINITY = " + (Double.POSITIVE_INFINITY - Double.POSITIVE_INFINITY));
+        System.out.println("INFINITY * ZERO = " + (Double.POSITIVE_INFINITY * ZERO));
+        System.out.println();
+    }
+
+    void operations_with_no_real_results_produce_NaN() {
+        System.out.println("Operations with no real results produce NaN");
+        System.out.println("SQUARE ROOT OF -1 = " + Math.sqrt(-1));
+        System.out.println("LOG OF -1 = " + Math.log(-1));
+        System.out.println();
+    }
+
+    void operations_with_NaN_produce_NaN() {
+        System.out.println("Operations with NaN produce NaN");
+        System.out.println("2 + NaN = " + (2 + Double.NaN));
+        System.out.println("2 - NaN = " + (2 - Double.NaN));
+        System.out.println("2 * NaN = " + (2 * Double.NaN));
+        System.out.println("2 / NaN = " + (2 / Double.NaN));
+        System.out.println();
+    }
+
+    void assign_NaN_to_missing_values() {
+        System.out.println("Assign NaN to Missing values");
+        double salaryRequired = Double.NaN;
+        System.out.println(salaryRequired);
+        System.out.println();
+    }
+
+    void comparison_with_NaN() {
+        System.out.println("Comparison with NaN");
+        final double NAN = Double.NaN;
+        System.out.println("NaN == 1 = " + (NAN == 1));
+        System.out.println("NaN > 1 = " + (NAN > 1));
+        System.out.println("NaN < 1 = " + (NAN < 1));
+        System.out.println("NaN != 1 = " + (NAN != 1));
+        System.out.println("NaN == NaN = " + (NAN == NAN));
+        System.out.println("NaN > NaN = " + (NAN > NAN));
+        System.out.println("NaN < NaN = " + (NAN < NAN));
+        System.out.println("NaN != NaN = " + (NAN != NAN));
+        System.out.println();
+    }
+
+    void check_if_a_value_is_NaN() {
+        System.out.println("Check if a value is NaN");
+        double x = 1;
+        System.out.println(x + " is NaN = " + (x != x));
+        System.out.println(x + " is NaN = " + (Double.isNaN(x)));
+
+        x = Double.NaN;
+        System.out.println(x + " is NaN = " + (x != x));
+        System.out.println(x + " is NaN = " + (Double.isNaN(x)));
+        System.out.println();
+    }
+
+}

core-java/src/main/java/com/baeldung/numberofdigits/NumberOfDigitsDriver.java

@@ -1,10 +1,12 @@
 package com.baeldung.numberofdigits;
 
-import static com.baeldung.designpatterns.util.LogerUtil.LOG;
+import org.apache.log4j.Logger;
 
 public class NumberOfDigitsDriver {
     private static NumberOfDigits numberOfDigits;
     
+    private static Logger LOG = Logger.getLogger(NumberOfDigitsDriver.class);
+    
     static {
         numberOfDigits = new NumberOfDigits();
     }

core-java/src/main/java/com/baeldung/scope/method/BaseMethodClass.java

@@ -0,0 +1,9 @@
+package com.baeldung.scope.method;
+
+
+public class BaseMethodClass {
+
+    public static void printMessage() {
+        System.out.println("base static method");
+    }
+}

core-java/src/main/java/com/baeldung/scope/method/ChildMethodClass.java

@@ -0,0 +1,9 @@
+package com.baeldung.scope.method;
+
+
+public class ChildMethodClass extends BaseMethodClass {
+
+    public static void printMessage() {
+        System.out.println("child static method");
+    }
+}

core-java/src/main/java/com/baeldung/scope/method/MethodHidingDemo.java

@@ -0,0 +1,8 @@
+package com.baeldung.scope.method;
+
+public class MethodHidingDemo {
+
+    public static void main(String[] args) {
+        ChildMethodClass.printMessage();
+    }
+}

core-java/src/main/java/com/baeldung/scope/variable/ChildVariable.java

@@ -0,0 +1,13 @@
+package com.baeldung.scope.variable;
+
+/**
+ * Created by Gebruiker on 5/7/2018.
+ */
+public class ChildVariable extends ParentVariable {
+
+    String instanceVariable = "child variable";
+
+    public void printInstanceVariable() {
+        System.out.println(instanceVariable);
+    }
+}

core-java/src/main/java/com/baeldung/scope/variable/HideVariable.java

@@ -0,0 +1,23 @@
+package com.baeldung.scope.variable;
+
+/**
+ * Created by Gebruiker on 5/6/2018.
+ */
+public class HideVariable {
+
+    private String message = "this is instance variable";
+
+    HideVariable() {
+        String message = "constructor local variable";
+        System.out.println(message);
+    }
+
+    public void printLocalVariable() {
+        String message = "method local variable";
+        System.out.println(message);
+    }
+
+    public void printInstanceVariable() {
+        System.out.println(this.message);
+    }
+}

core-java/src/main/java/com/baeldung/scope/variable/ParentVariable.java

@@ -0,0 +1,13 @@
+package com.baeldung.scope.variable;
+
+/**
+ * Created by Gebruiker on 5/7/2018.
+ */
+public class ParentVariable {
+
+    String instanceVariable = "parent variable";
+
+    public void printInstanceVariable() {
+        System.out.println(instanceVariable);
+    }
+}

core-java/src/main/java/com/baeldung/scope/variable/VariableHidingDemo.java

@@ -0,0 +1,18 @@
+package com.baeldung.scope.variable;
+
+/**
+ * Created by Gebruiker on 5/6/2018.
+ */
+public class VariableHidingDemo {
+    public static void main(String[] args) {
+        HideVariable variable = new HideVariable();
+        variable.printLocalVariable();
+        variable.printInstanceVariable();
+
+        ParentVariable parentVariable = new ParentVariable();
+        ParentVariable childVariable = new ChildVariable();
+
+        parentVariable.printInstanceVariable();
+        childVariable.printInstanceVariable();
+    }
+}

core-java/src/main/java/com/baeldung/stringisnumeric/Benchmarking.java

@@ -0,0 +1,75 @@
+package com.baeldung.stringisnumeric;
+
+import java.util.concurrent.TimeUnit;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.runner.Runner;
+import org.openjdk.jmh.runner.RunnerException;
+import org.openjdk.jmh.runner.options.Options;
+import org.openjdk.jmh.runner.options.OptionsBuilder;
+
+
+public class Benchmarking {
+    public static void main(String[] args) throws RunnerException {
+        Options opt = new OptionsBuilder()
+                .include(Benchmarking.class.getSimpleName())
+                .forks(1)
+                .build();
+
+        new Runner(opt).run();
+    }
+
+    @State(Scope.Thread)
+    public static class ExecutionPlan {
+        public String number = Integer.toString(Integer.MAX_VALUE);
+        public boolean isNumber = false;
+        public IsNumeric isNumeric= new IsNumeric();
+    }
+    
+    @Benchmark 
+    @BenchmarkMode(Mode.AverageTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    public void usingCoreJava(ExecutionPlan plan) {
+        plan.isNumber = plan.isNumeric.usingCoreJava(plan.number);
+    }
+    
+    @Benchmark 
+    @BenchmarkMode(Mode.AverageTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    public void usingRegularExpressions(ExecutionPlan plan) {
+        plan.isNumber = plan.isNumeric.usingRegularExpressions(plan.number);
+    }
+    
+    @Benchmark 
+    @BenchmarkMode(Mode.AverageTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    public void usingNumberUtils_isCreatable(ExecutionPlan plan) {
+        plan.isNumber = plan.isNumeric.usingNumberUtils_isCreatable(plan.number);
+    }
+    
+    @Benchmark 
+    @BenchmarkMode(Mode.AverageTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    public void usingNumberUtils_isParsable(ExecutionPlan plan) {
+        plan.isNumber = plan.isNumeric.usingNumberUtils_isParsable(plan.number);
+    }
+    
+    @Benchmark 
+    @BenchmarkMode(Mode.AverageTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    public void usingStringUtils_isNumeric(ExecutionPlan plan) {
+        plan.isNumber = plan.isNumeric.usingStringUtils_isNumeric(plan.number);
+    }
+    
+    @Benchmark 
+    @BenchmarkMode(Mode.AverageTime)
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    public void usingStringUtils_isNumericSpace(ExecutionPlan plan) {
+        plan.isNumber = plan.isNumeric.usingStringUtils_isNumericSpace(plan.number);
+    }
+}

core-java/src/main/java/com/baeldung/stringisnumeric/IsNumeric.java

@@ -0,0 +1,35 @@
+package com.baeldung.stringisnumeric;
+
+import org.apache.commons.lang3.StringUtils;
+import org.apache.commons.lang3.math.NumberUtils;
+
+public class IsNumeric {
+    public boolean usingCoreJava(String strNum) {
+        try {
+            double d = Double.parseDouble(strNum);
+        } catch (NumberFormatException | NullPointerException nfe) {
+            return false;
+        }
+        return true;
+    }
+    
+    public boolean usingRegularExpressions(String strNum) {
+        return strNum.matches("-?\\d+(\\.\\d+)?");
+    }
+    
+    public boolean usingNumberUtils_isCreatable(String strNum) {
+        return NumberUtils.isCreatable(strNum);
+    }
+    
+    public boolean usingNumberUtils_isParsable(String strNum) {
+        return NumberUtils.isParsable(strNum);
+    }
+    
+    public boolean usingStringUtils_isNumeric(String strNum) {
+        return StringUtils.isNumeric(strNum);
+    }
+    
+    public boolean usingStringUtils_isNumericSpace(String strNum) {
+        return StringUtils.isNumericSpace(strNum);
+    }
+}

core-java/src/main/java/com/baeldung/stringisnumeric/IsNumericDriver.java

@@ -0,0 +1,34 @@
+package com.baeldung.stringisnumeric;
+
+import org.apache.log4j.Logger;
+
+public class IsNumericDriver {
+    private static IsNumeric isNumeric;
+    private static Logger LOG = Logger.getLogger(IsNumericDriver.class);
+    static {
+        isNumeric =new IsNumeric();
+        
+    }
+    
+    public static void main(String[] args) {
+        LOG.info("Testing all methods...");
+        
+        boolean res = isNumeric.usingCoreJava("1001");
+        LOG.info("Using Core Java : " + res);
+        
+        res = isNumeric.usingRegularExpressions("1001");
+        LOG.info("Using Regular Expressions : " + res);
+        
+        res =isNumeric.usingNumberUtils_isCreatable("1001");
+        LOG.info("Using NumberUtils.isCreatable : " + res);
+        
+        res =isNumeric.usingNumberUtils_isParsable("1001");
+        LOG.info("Using NumberUtils.isParsable : " + res);
+        
+        res =isNumeric.usingStringUtils_isNumeric("1001");
+        LOG.info("Using StringUtils.isNumeric : " + res);
+        
+        res =isNumeric.usingStringUtils_isNumericSpace("1001");
+        LOG.info("Using StringUtils.isNumericSpace : " + res);
+    }
+}

core-java/src/test/java/com/baeldung/stringisnumeric/CoreJavaIsNumericUnitTest.java

@@ -0,0 +1,31 @@
+package com.baeldung.stringisnumeric;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class CoreJavaIsNumericUnitTest {
+    public static boolean isNumeric(String strNum) {
+        try {
+            double d = Double.parseDouble(strNum);
+        } catch (NumberFormatException | NullPointerException nfe) {
+            return false;
+        }
+        return true;
+    }
+    
+    @Test
+    public void whenUsingCoreJava_thenTrue() {
+        // Valid Numbers
+        assertThat(isNumeric("22")).isTrue();
+        assertThat(isNumeric("5.05")).isTrue();
+        assertThat(isNumeric("-200")).isTrue(); 
+        assertThat(isNumeric("10.0d")).isTrue();
+        assertThat(isNumeric("   22   ")).isTrue();
+         
+        // Invalid Numbers
+        assertThat(isNumeric(null)).isFalse();
+        assertThat(isNumeric("")).isFalse();
+        assertThat(isNumeric("abc")).isFalse();
+    }
+}

core-java/src/test/java/com/baeldung/stringisnumeric/NumberUtilsIsCreatableUnitTest.java

@@ -0,0 +1,28 @@
+package com.baeldung.stringisnumeric;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.apache.commons.lang3.math.NumberUtils;
+import org.junit.Test;
+
+public class NumberUtilsIsCreatableUnitTest {
+    @Test
+    public void givenApacheCommons_whenUsingIsParsable_thenTrue() {
+        // Valid Numbers
+        assertThat(NumberUtils.isCreatable("22")).isTrue();
+        assertThat(NumberUtils.isCreatable("5.05")).isTrue();
+        assertThat(NumberUtils.isCreatable("-200")).isTrue();
+        assertThat(NumberUtils.isCreatable("10.0d")).isTrue();
+        assertThat(NumberUtils.isCreatable("1000L")).isTrue();
+        assertThat(NumberUtils.isCreatable("0xFF")).isTrue();
+        assertThat(NumberUtils.isCreatable("07")).isTrue();
+        assertThat(NumberUtils.isCreatable("2.99e+8")).isTrue();
+         
+        // Invalid Numbers
+        assertThat(NumberUtils.isCreatable(null)).isFalse();
+        assertThat(NumberUtils.isCreatable("")).isFalse();
+        assertThat(NumberUtils.isCreatable("abc")).isFalse();
+        assertThat(NumberUtils.isCreatable(" 22 ")).isFalse();
+        assertThat(NumberUtils.isCreatable("09")).isFalse();
+    }
+}

core-java/src/test/java/com/baeldung/stringisnumeric/NumberUtilsIsParsableUnitTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.stringisnumeric;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.apache.commons.lang3.math.NumberUtils;
+import org.junit.Test;
+
+public class NumberUtilsIsParsableUnitTest {
+    @Test
+    public void givenApacheCommons_whenUsingIsParsable_thenTrue() {
+        // Valid Numbers
+        assertThat(NumberUtils.isParsable("22")).isTrue();
+        assertThat(NumberUtils.isParsable("-23")).isTrue();
+        assertThat(NumberUtils.isParsable("2.2")).isTrue();
+        assertThat(NumberUtils.isParsable("09")).isTrue();
+        
+        // Invalid Numbers
+        assertThat(NumberUtils.isParsable(null)).isFalse();
+        assertThat(NumberUtils.isParsable("")).isFalse();
+        assertThat(NumberUtils.isParsable("6.2f")).isFalse();
+        assertThat(NumberUtils.isParsable("9.8d")).isFalse();
+        assertThat(NumberUtils.isParsable("22L")).isFalse();
+        assertThat(NumberUtils.isParsable("0xFF")).isFalse();
+        assertThat(NumberUtils.isParsable("2.99e+8")).isFalse();
+    }
+}

core-java/src/test/java/com/baeldung/stringisnumeric/RegularExpressionsUnitTest.java

@@ -0,0 +1,22 @@
+package com.baeldung.stringisnumeric;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class RegularExpressionsUnitTest {
+    public static boolean isNumeric(String strNum) {
+        return strNum.matches("-?\\d+(\\.\\d+)?");
+    }
+    
+    @Test
+    public void whenUsingRegularExpressions_thenTrue() {
+        // Valid Numbers
+        assertThat(isNumeric("22")).isTrue();
+        assertThat(isNumeric("5.05")).isTrue();
+        assertThat(isNumeric("-200")).isTrue();
+         
+        // Invalid Numbers
+        assertThat(isNumeric("abc")).isFalse();
+    }
+}

core-java/src/test/java/com/baeldung/stringisnumeric/StringUtilsIsNumericSpaceUnitTest.java

@@ -0,0 +1,23 @@
+package com.baeldung.stringisnumeric;
+
+import org.apache.commons.lang3.StringUtils;
+import org.junit.Test;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class StringUtilsIsNumericSpaceUnitTest {
+    @Test
+    public void givenApacheCommons_whenUsingIsNumericSpace_thenTrue() {
+        // Valid Numbers
+        assertThat(StringUtils.isNumericSpace("123")).isTrue();
+        assertThat(StringUtils.isNumericSpace("١٢٣")).isTrue();
+        assertThat(StringUtils.isNumericSpace("")).isTrue();
+        assertThat(StringUtils.isNumericSpace("  ")).isTrue();
+        assertThat(StringUtils.isNumericSpace("12 3")).isTrue();
+         
+        // Invalid Numbers
+        assertThat(StringUtils.isNumericSpace(null)).isFalse();
+        assertThat(StringUtils.isNumericSpace("ab2c")).isFalse();
+        assertThat(StringUtils.isNumericSpace("12.3")).isFalse();
+        assertThat(StringUtils.isNumericSpace("-123")).isFalse();
+    }
+}

core-java/src/test/java/com/baeldung/stringisnumeric/StringUtilsIsNumericUnitTest.java

@@ -0,0 +1,24 @@
+package com.baeldung.stringisnumeric;
+
+import org.apache.commons.lang3.StringUtils;
+import org.junit.Test;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class StringUtilsIsNumericUnitTest {
+    @Test
+    public void givenApacheCommons_whenUsingIsNumeric_thenTrue() {
+        // Valid Numbers
+        assertThat(StringUtils.isNumeric("123")).isTrue();
+        assertThat(StringUtils.isNumeric("١٢٣")).isTrue();
+        assertThat(StringUtils.isNumeric("१२३")).isTrue();
+         
+        // Invalid Numbers
+        assertThat(StringUtils.isNumeric(null)).isFalse();
+        assertThat(StringUtils.isNumeric("")).isFalse();
+        assertThat(StringUtils.isNumeric("  ")).isFalse();
+        assertThat(StringUtils.isNumeric("12 3")).isFalse();
+        assertThat(StringUtils.isNumeric("ab2c")).isFalse();
+        assertThat(StringUtils.isNumeric("12.3")).isFalse();
+        assertThat(StringUtils.isNumeric("-123")).isFalse();
+    }
+}

core-kotlin/pom.xml

@@ -63,6 +63,24 @@
             <artifactId>kotlinx-coroutines-core</artifactId>
             <version>${kotlinx.version}</version>
         </dependency>
+        <dependency>
+            <groupId>org.jetbrains.spek</groupId>
+            <artifactId>spek-api</artifactId>
+            <version>1.1.5</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.jetbrains.spek</groupId>
+            <artifactId>spek-subject-extension</artifactId>
+            <version>1.1.5</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.jetbrains.spek</groupId>
+            <artifactId>spek-junit-platform-engine</artifactId>
+            <version>1.1.5</version>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>com.nhaarman</groupId>
             <artifactId>mockito-kotlin</artifactId>

core-kotlin/src/test/kotlin/com/baeldung/kotlin/spek/CalculatorSubjectTest5.kt

@@ -0,0 +1,19 @@
+package com.baeldung.kotlin.spek
+
+import com.baeldung.kotlin.junit5.Calculator
+import org.jetbrains.spek.api.dsl.describe
+import org.jetbrains.spek.api.dsl.it
+import org.jetbrains.spek.subject.SubjectSpek
+import org.junit.jupiter.api.Assertions.assertEquals
+
+class CalculatorSubjectTest5 : SubjectSpek<Calculator>({
+    subject { Calculator() }
+    describe("A calculator") {
+        describe("Addition") {
+            val result = subject.add(3, 5)
+            it("Produces the correct answer") {
+                assertEquals(8, result)
+            }
+        }
+    }
+})

core-kotlin/src/test/kotlin/com/baeldung/kotlin/spek/CalculatorTest5.kt

@@ -0,0 +1,32 @@
+package com.baeldung.kotlin.spek
+
+import com.baeldung.kotlin.junit5.Calculator
+import org.jetbrains.spek.api.Spek
+import org.jetbrains.spek.api.dsl.describe
+import org.jetbrains.spek.api.dsl.given
+import org.jetbrains.spek.api.dsl.it
+import org.jetbrains.spek.api.dsl.on
+import org.junit.jupiter.api.Assertions.assertEquals
+
+class CalculatorTest5 : Spek({
+    given("A calculator") {
+        val calculator = Calculator()
+        on("Adding 3 and 5") {
+            val result = calculator.add(3, 5)
+            it("Produces 8") {
+                assertEquals(8, result)
+            }
+        }
+    }
+
+    describe("A calculator") {
+        val calculator = Calculator()
+        describe("Addition") {
+            val result = calculator.add(3, 5)
+            it("Produces the correct answer") {
+                assertEquals(8, result)
+            }
+        }
+    }
+
+})