3-Third commit for articles:

* to core-java-lang:
  * https://www.baeldung.com/java-lang-system
  * https://www.baeldung.com/java-type-erasure
  * https://www.baeldung.com/java-assert
  * https://www.baeldung.com/java-pass-by-value-or-pass-by-reference
  * https://www.baeldung.com/java-variable-method-hiding
  * https://www.baeldung.com/java-access-modifiers
  * https://www.baeldung.com/java-super
  * https://www.baeldung.com/java-this
  * https://www.baeldung.com/java-immutable-object
  * https://www.baeldung.com/java-classnotfoundexception-and-noclassdeffounderror
  * https://www.baeldung.com/infinite-loops-java (changes for this were included in commit 1, with other loop-related examples)

core-java-lang/src/main/java/com/baeldung/accessmodifiers/Public.java

@@ -0,0 +1,9 @@
+package com.baeldung.accessmodifiers;
+
+public class Public {
+    public Public() {
+        SuperPublic.publicMethod(); // Available everywhere.
+        SuperPublic.protectedMethod(); // Available in the same package or subclass.
+        SuperPublic.defaultMethod(); // Available in the same package.
+    }
+}

core-java-lang/src/main/java/com/baeldung/accessmodifiers/SubClass.java

@@ -0,0 +1,9 @@
+package com.baeldung.accessmodifiers;
+
+public class SubClass extends SuperPublic {
+    public SubClass() {
+        SuperPublic.publicMethod(); // Available everywhere.
+        SuperPublic.protectedMethod(); // Available in the same package or subclass.
+        SuperPublic.defaultMethod(); // Available in the same package.
+    }
+}

core-java-lang/src/main/java/com/baeldung/accessmodifiers/SuperPublic.java

@@ -0,0 +1,39 @@
+package com.baeldung.accessmodifiers;
+
+//Only public or default access modifiers are permitted
+public class SuperPublic {
+    // Always available from anywhere
+    static public void publicMethod() {
+        System.out.println(SuperPublic.class.getName() + " publicMethod()");
+    }
+    
+    // Available within the same package
+    static void defaultMethod() {
+        System.out.println(SuperPublic.class.getName() + " defaultMethod()");
+    }
+    
+    // Available within the same package and subclasses
+    static protected void protectedMethod() {
+        System.out.println(SuperPublic.class.getName() + " protectedMethod()");
+    }
+    
+    // Available within the same class only
+    static private void privateMethod() {
+        System.out.println(SuperPublic.class.getName() + " privateMethod()");
+    }
+    
+    // Method in the same class = has access to all members within the same class
+    private void anotherPrivateMethod() {
+        privateMethod();
+        defaultMethod();
+        protectedMethod();
+        publicMethod(); // Available in the same class only.
+    }
+}
+
+// Only public or default access modifiers are permitted
+class SuperDefault {
+    public void publicMethod() {
+        System.out.println(this.getClass().getName() + " publicMethod()");
+    }
+}

core-java-lang/src/main/java/com/baeldung/accessmodifiers/another/AnotherPublic.java

@@ -0,0 +1,9 @@
+package com.baeldung.accessmodifiers.another;
+
+import com.baeldung.accessmodifiers.SuperPublic;
+
+public class AnotherPublic {
+    public AnotherPublic() {
+        SuperPublic.publicMethod(); // Available everywhere.
+    }
+}

core-java-lang/src/main/java/com/baeldung/accessmodifiers/another/AnotherSubClass.java

@@ -0,0 +1,10 @@
+package com.baeldung.accessmodifiers.another;
+
+import com.baeldung.accessmodifiers.SuperPublic;
+
+public class AnotherSubClass extends SuperPublic {
+    public AnotherSubClass() {
+        SuperPublic.publicMethod(); // Available everywhere.
+        SuperPublic.protectedMethod(); // Available in subclass. Let's note different package.
+    }
+}

core-java-lang/src/main/java/com/baeldung/accessmodifiers/another/AnotherSuperPublic.java

@@ -0,0 +1,9 @@
+package com.baeldung.accessmodifiers.another;
+
+import com.baeldung.accessmodifiers.SuperPublic;
+
+public class AnotherSuperPublic {
+    public AnotherSuperPublic() {
+        SuperPublic.publicMethod(); // Available everywhere. Let's note different package.
+    }
+}

core-java-lang/src/main/java/com/baeldung/assertion/Assertion.java

@@ -0,0 +1,26 @@
+package com.baeldung.assertion;
+
+/**
+ * Simple demonstration of using Java assert keyword.
+ */
+public class Assertion {
+
+  public static void main(String[] args) {
+    Assertion assertion = new Assertion();
+    assertion.setup();
+  }
+
+  public void setup() {
+    Object conn = getConnection();
+    assert conn != null : "Connection is null";
+
+    // continue with other setup ...
+  }
+
+  // Simulate failure to get a connection; using Object
+  // to avoid dependencies on JDBC or some other heavy
+  // 3rd party library
+  public Object getConnection() {
+    return null;
+  }
+}

core-java-lang/src/main/java/com/baeldung/immutableobjects/Currency.java

@@ -0,0 +1,18 @@
+package com.baeldung.immutableobjects;
+
+public final class Currency {
+
+    private final String value;
+    
+    private Currency(String currencyValue) {
+        value = currencyValue;
+    }
+    
+    public String getValue() {
+        return value;
+    }
+    
+    public static Currency of(String value) {
+        return new Currency(value);
+    }
+}

core-java-lang/src/main/java/com/baeldung/immutableobjects/Money.java

@@ -0,0 +1,20 @@
+package com.baeldung.immutableobjects;
+
+// 4. Immutability in Java
+public final class Money {
+    private final double amount;
+    private final Currency currency;
+
+    public Money(double amount, Currency currency) {
+        this.amount = amount;
+        this.currency = currency;
+    }
+
+    public Currency getCurrency() {
+        return currency;
+    }
+
+    public double getAmount() {
+        return amount;
+    }
+}

core-java-lang/src/main/java/com/baeldung/keyword/KeywordDemo.java

@@ -0,0 +1,16 @@
+package com.baeldung.keyword;
+
+import com.baeldung.keyword.superkeyword.SuperSub;
+import com.baeldung.keyword.thiskeyword.KeywordUnitTest;
+
+/**
+ * Created by Gebruiker on 5/14/2018.
+ */
+public class KeywordDemo {
+
+    public static void main(String[] args) {
+        KeywordUnitTest keyword = new KeywordUnitTest();
+
+        SuperSub child = new SuperSub("message from the child class");
+    }
+}

core-java-lang/src/main/java/com/baeldung/keyword/superkeyword/SuperBase.java

@@ -0,0 +1,20 @@
+package com.baeldung.keyword.superkeyword;
+
+/**
+ * Created by Gebruiker on 5/14/2018.
+ */
+public class SuperBase {
+
+    String message = "super class";
+
+    public SuperBase() {
+    }
+
+    public SuperBase(String message) {
+        this.message = message;
+    }
+
+    public void printMessage() {
+        System.out.println(message);
+    }
+}

core-java-lang/src/main/java/com/baeldung/keyword/superkeyword/SuperSub.java

@@ -0,0 +1,26 @@
+package com.baeldung.keyword.superkeyword;
+
+/**
+ * Created by Gebruiker on 5/15/2018.
+ */
+public class SuperSub extends SuperBase {
+
+    String message = "child class";
+
+    public SuperSub(String message) {
+        super(message);
+    }
+
+    public SuperSub() {
+        super.printMessage();
+        printMessage();
+    }
+
+    public void getParentMessage() {
+        System.out.println(super.message);
+    }
+
+    public void printMessage() {
+        System.out.println(message);
+    }
+}

core-java-lang/src/main/java/com/baeldung/keyword/thiskeyword/KeywordUnitTest.java

@@ -0,0 +1,49 @@
+package com.baeldung.keyword.thiskeyword;
+
+public class KeywordUnitTest {
+
+    private String name;
+    private int age;
+
+    public KeywordUnitTest() {
+        this("John", 27);
+        this.printMessage();
+        printInstance(this);
+    }
+
+    public KeywordUnitTest(String name, int age) {
+        this.name = name;
+        this.age = age;
+    }
+
+    public void printMessage() {
+        System.out.println("invoked by this");
+    }
+
+    public void printInstance(KeywordUnitTest thisKeyword) {
+        System.out.println(thisKeyword);
+    }
+
+    public KeywordUnitTest getCurrentInstance() {
+        return this;
+    }
+
+    class ThisInnerClass {
+
+        boolean isInnerClass = true;
+
+        public ThisInnerClass() {
+            KeywordUnitTest thisKeyword = KeywordUnitTest.this;
+            String outerString = KeywordUnitTest.this.name;
+            System.out.println(this.isInnerClass);
+        }
+    }
+
+    @Override
+    public String toString() {
+        return "KeywordTest{" +
+                "name='" + name + '\'' +
+                ", age=" + age +
+                '}';
+    }
+}

core-java-lang/src/main/java/com/baeldung/noclassdeffounderror/ClassWithInitErrors.java

@@ -0,0 +1,5 @@
+package com.baeldung.noclassdeffounderror;
+
+public class ClassWithInitErrors {
+    static int data = 1 / 0;
+}

core-java-lang/src/main/java/com/baeldung/noclassdeffounderror/NoClassDefFoundErrorExample.java

@@ -0,0 +1,14 @@
+package com.baeldung.noclassdeffounderror;
+
+public class NoClassDefFoundErrorExample {
+    public ClassWithInitErrors getClassWithInitErrors() {
+        ClassWithInitErrors test;
+        try {
+            test = new ClassWithInitErrors();
+        } catch (Throwable t) {
+            System.out.println(t);
+        }
+        test = new ClassWithInitErrors();
+        return test;
+    }
+}

core-java-lang/src/main/java/com/baeldung/parameterpassing/NonPrimitives.java

@@ -0,0 +1,27 @@
+package com.baeldung.parameterpassing;
+
+public class NonPrimitives {
+    public static void main(String[] args) {
+        FooClass a = new FooClass(1);
+        FooClass b = new FooClass(1);
+ 
+        System.out.printf("Before Modification: a = %d and b = %d ", a.num, b.num);
+        modify(a, b);
+        System.out.printf("\nAfter Modification: a = %d and b = %d ", a.num, b.num);
+    }
+ 
+    public static void modify(FooClass a1, FooClass b1) {
+        a1.num++;
+       
+        b1 = new FooClass(1);
+        b1.num++;
+    }
+}
+ 
+class FooClass {
+    public int num;
+   
+    public FooClass(int num) {
+        this.num = num;
+    }
+}

core-java-lang/src/main/java/com/baeldung/parameterpassing/Primitives.java

@@ -0,0 +1,17 @@
+package com.baeldung.parameterpassing;
+
+public class Primitives {
+    public static void main(String[] args) {
+        int x = 1;
+        int y = 2;
+       
+        System.out.printf("Before Modification: x = %d and y = %d ", x, y);
+        modify(x, y);
+        System.out.printf("\nAfter Modification: x = %d and y = %d ", x, y);
+    }
+   
+    public static void modify(int x1, int y1) {
+        x1 = 5;
+        y1 = 10;
+    }
+}

core-java-lang/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-lang/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-lang/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-lang/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-lang/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-lang/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-lang/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-lang/src/main/java/com/baeldung/system/ChatWindow.java

@@ -0,0 +1,17 @@
+package com.baeldung.system;
+
+import java.awt.event.WindowEvent;
+
+/**
+ * Note: This class is not meant for unit-testing since it uses system
+ * features at low level and that it uses 'System' gc() which suggests
+ * JVM for garbage collection. But the usage below demonstrates how the
+ * method can be used.
+ */
+public class ChatWindow {
+    public void windowStateChanged(WindowEvent event) {
+        if (event.getNewState() == WindowEvent.WINDOW_DEACTIVATED ) {
+            System.gc(); // if it ends up running, great!
+        }
+    }
+}

core-java-lang/src/main/java/com/baeldung/system/DateTimeService.java

@@ -0,0 +1,16 @@
+package com.baeldung.system;
+
+import java.util.Date;
+
+public class DateTimeService {
+
+    // One hour from now
+    public long nowPlusOneHour() {
+        return System.currentTimeMillis() + 3600 * 1000L;
+    }
+
+    // Human-readable format
+    public String nowPrettyPrinted() {
+        return new Date(System.currentTimeMillis()).toString();
+    }
+}

core-java-lang/src/main/java/com/baeldung/system/EnvironmentVariables.java

@@ -0,0 +1,7 @@
+package com.baeldung.system;
+
+public class EnvironmentVariables {
+    public String getPath() {
+        return System.getenv("PATH");
+    }
+}

core-java-lang/src/main/java/com/baeldung/system/SystemErrDemo.java

@@ -0,0 +1,18 @@
+package com.baeldung.system;
+
+/**
+ * Note: This class is not meant for unit-testing since it uses system
+ * features at low level and that it uses 'System' standard error stream
+ * methods to show output on screen. Also unit-tests in CI environments
+ * don't have console output for user to see messages. But the usage below
+ * demonstrates how the methods can be used.
+ */
+public class SystemErrDemo {
+    public static void main(String[] args) {
+        // Print without 'hitting' return
+        System.err.print("some inline error message");
+
+        // Print and then 'hit' return
+        System.err.println("an error message having new line at the end");
+    }
+}

core-java-lang/src/main/java/com/baeldung/system/SystemExitDemo.java

@@ -0,0 +1,24 @@
+package com.baeldung.system;
+
+/**
+ * Note: This class is not meant for unit-testing since it uses system
+ * features at low level and that it uses 'System' exit() which will
+ * exit the JVM. Also unit-tests in CI environments are not meant to
+ * exit unit tests like that. But the usage below demonstrates how the
+ * method can be used.
+ */
+public class SystemExitDemo {
+    public static void main(String[] args) {
+        boolean error = false;
+
+        // do something and set error value
+
+        if (error) {
+            System.exit(1); // error case exit
+        } else {
+            System.exit(0); // normal case exit
+        }
+
+        // Will not do anything after exit()
+    }
+}

core-java-lang/src/main/java/com/baeldung/system/SystemOutDemo.java

@@ -0,0 +1,25 @@
+package com.baeldung.system;
+
+import java.io.FileNotFoundException;
+import java.io.PrintStream;
+
+/**
+ * Note: This class is not meant for unit-testing since it uses system
+ * features at low level and that it uses 'System' standard output stream
+ * methods to show output on screen. Also unit-tests in CI environments
+ * don't have console output for user to see messages. But the usage below
+ * demonstrates how the methods can be used.
+ */
+public class SystemOutDemo {
+
+    public static void main(String[] args) throws FileNotFoundException {
+        // Print without 'hitting' return
+        System.out.print("some inline message");
+
+        // Print and then 'hit' return
+        System.out.println("a message having new line at the end");
+
+        // Changes output stream to send messages to file.
+        System.setOut(new PrintStream("file.txt"));
+    }
+}

core-java-lang/src/main/java/com/baeldung/system/UserCredentials.java

@@ -0,0 +1,35 @@
+package com.baeldung.system;
+
+import java.io.BufferedReader;
+import java.io.Console;
+import java.io.IOException;
+import java.io.InputStreamReader;
+
+/**
+ * Note: This class is not meant for unit-testing since it uses system
+ * features at low level and that it uses 'System' standard input stream
+ * methods to read text from user. Also unit-tests in CI environments
+ * don't have console input for user to type in text. But the usage below
+ * demonstrates how the methods can be used.
+ */
+public class UserCredentials {
+
+    public String readUsername(int length) throws IOException {
+        byte[] name = new byte[length];
+        System.in.read(name, 0, length); // by default, from the console
+        return new String(name);
+    }
+
+    public String readUsername() throws IOException {
+        BufferedReader reader =
+                new BufferedReader(new InputStreamReader(System.in));
+        return reader.readLine();
+    }
+
+    public String readUsernameWithPrompt() {
+        Console console = System.console();
+
+        return console == null ? null : // Console not available
+                console.readLine("%s", "Enter your name: ");
+    }
+}

core-java-lang/src/main/java/com/baeldung/typeerasure/ArrayContentPrintUtil.java

@@ -0,0 +1,16 @@
+package com.baeldung.typeerasure;
+
+public class ArrayContentPrintUtil {
+
+   public static <E> void printArray(E[] array) {
+        for (E element : array) {
+            System.out.printf("%s ", element);
+        }
+    }
+    
+    public static <E extends Comparable<E>> void printArray(E[] array) {
+        for (E element : array) {
+            System.out.printf("%s ", element);
+        }
+    }
+}

core-java-lang/src/main/java/com/baeldung/typeerasure/BoundStack.java

@@ -0,0 +1,37 @@
+package com.baeldung.typeerasure;
+
+import java.util.Arrays;
+
+public class BoundStack<E extends Comparable<E>> {
+
+    private E[] stackContent;
+    private int total;
+
+    public BoundStack(int capacity) {
+        this.stackContent = (E[]) new Object[capacity];
+    }
+
+    public void push(E data) {
+        if (total == stackContent.length) {
+            resize(2 * stackContent.length);
+        }
+        stackContent[total++] = data;
+    }
+
+    public E pop() {
+        if (!isEmpty()) {
+            E datum = stackContent[total];
+            stackContent[total--] = null;
+            return datum;
+        }
+        return null;
+    }
+
+    private void resize(int capacity) {
+        Arrays.copyOf(stackContent, capacity);
+    }
+
+    public boolean isEmpty() {
+        return total == 0;
+    }
+}

core-java-lang/src/main/java/com/baeldung/typeerasure/IntegerStack.java

@@ -0,0 +1,13 @@
+package com.baeldung.typeerasure;
+
+public class IntegerStack extends Stack<Integer> {
+
+    public IntegerStack(int capacity) {
+        super(capacity);
+    }
+
+    public void push(Integer value) {
+        System.out.println("Pushing into my integerStack");
+        super.push(value);
+    }
+}

core-java-lang/src/main/java/com/baeldung/typeerasure/Stack.java

@@ -0,0 +1,39 @@
+package com.baeldung.typeerasure;
+
+import java.util.Arrays;
+
+public class Stack<E> {
+
+    private E[] stackContent;
+    private int total;
+
+    public Stack(int capacity) {
+        this.stackContent = (E[]) new Object[capacity];
+    }
+
+    public void push(E data) {
+        System.out.println("In base stack push#");
+        if (total == stackContent.length) {
+            resize(2 * stackContent.length);
+        }
+        stackContent[total++] = data;
+    }
+
+    public E pop() {
+        if (!isEmpty()) {
+            E datum = stackContent[total];
+            stackContent[total--] = null;
+            return datum;
+        }
+        return null;
+    }
+
+    private void resize(int capacity) {
+        Arrays.copyOf(stackContent, capacity);
+    }
+
+    public boolean isEmpty() {
+        return total == 0;
+    }
+
+}

core-java-lang/src/test/java/com/baeldung/classnotfoundexception/ClassNotFoundExceptionUnitTest.java

@@ -0,0 +1,11 @@
+package com.baeldung.classnotfoundexception;
+
+import org.junit.Test;
+
+public class ClassNotFoundExceptionUnitTest {
+
+    @Test(expected = ClassNotFoundException.class)
+    public void givenNoDriversInClassPath_whenLoadDrivers_thenClassNotFoundException() throws ClassNotFoundException {
+        Class.forName("oracle.jdbc.driver.OracleDriver");
+    }
+}

core-java-lang/src/test/java/com/baeldung/immutableobjects/ImmutableObjectsUnitTest.java

@@ -0,0 +1,36 @@
+package com.baeldung.immutableobjects;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.Test;
+
+public class ImmutableObjectsUnitTest {
+
+    @Test
+    public void whenCallingStringReplace_thenStringDoesNotMutate() {
+        // 2. What's an Immutable Object?
+        final String name = "baeldung";
+        final String newName = name.replace("dung", "----");
+
+        assertEquals("baeldung", name);
+        assertEquals("bael----", newName);
+    }
+
+    public void whenReassignFinalValue_thenCompilerError() {
+        // 3. The final Keyword in Java (1)
+        final String name = "baeldung";
+        // name = "bael...";
+    }
+
+    @Test
+    public void whenAddingElementToList_thenSizeChange() {
+        // 3. The final Keyword in Java (2)
+        final List<String> strings = new ArrayList<>();
+        assertEquals(0, strings.size());
+        strings.add("baeldung");
+        assertEquals(1, strings.size());
+    }
+}

core-java-lang/src/test/java/com/baeldung/noclassdeffounderror/NoClassDefFoundErrorUnitTest.java

@@ -0,0 +1,12 @@
+package com.baeldung.noclassdeffounderror;
+
+import org.junit.Test;
+
+public class NoClassDefFoundErrorUnitTest {
+
+    @Test(expected = NoClassDefFoundError.class)
+    public void givenInitErrorInClass_whenloadClass_thenNoClassDefFoundError() {
+        NoClassDefFoundErrorExample sample = new NoClassDefFoundErrorExample();
+        sample.getClassWithInitErrors();
+    }
+}

core-java-lang/src/test/java/com/baeldung/parameterpassing/NonPrimitivesUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.parameterpassing;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class NonPrimitivesUnitTest {
+    @Test
+    public void whenModifyingObjects_thenOriginalObjectChanged() {
+        Foo a = new Foo(1);
+        Foo b = new Foo(1);
+
+        // Before Modification
+        Assert.assertEquals(a.num, 1);
+        Assert.assertEquals(b.num, 1);
+        
+        modify(a, b);
+        
+        // After Modification
+        Assert.assertEquals(a.num, 2);
+        Assert.assertEquals(b.num, 1);
+    }
+ 
+    public static void modify(Foo a1, Foo b1) {
+        a1.num++;
+       
+        b1 = new Foo(1);
+        b1.num++;
+    }
+}
+ 
+class Foo {
+    public int num;
+   
+    public Foo(int num) {
+        this.num = num;
+    }
+}

core-java-lang/src/test/java/com/baeldung/parameterpassing/PrimitivesUnitTest.java

@@ -0,0 +1,28 @@
+package com.baeldung.parameterpassing;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class PrimitivesUnitTest {
+    @Test
+    public void whenModifyingPrimitives_thenOriginalValuesNotModified() {
+        
+        int x = 1;
+        int y = 2;
+       
+        // Before Modification
+        Assert.assertEquals(x, 1);
+        Assert.assertEquals(y, 2);
+        
+        modify(x, y);
+        
+        // After Modification
+        Assert.assertEquals(x, 1);
+        Assert.assertEquals(y, 2);
+    }
+    
+    public static void modify(int x1, int y1) {
+        x1 = 5;
+        y1 = 10;
+    }
+}

core-java-lang/src/test/java/com/baeldung/system/DateTimeServiceUnitTest.java

@@ -0,0 +1,15 @@
+package com.baeldung.system;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class DateTimeServiceUnitTest {
+
+    @Test
+    public void givenClass_whenCalledMethods_thenNotNullInResult() {
+        DateTimeService dateTimeService = new DateTimeService();
+
+        Assert.assertNotNull(dateTimeService.nowPlusOneHour());
+        Assert.assertNotNull(dateTimeService.nowPrettyPrinted());
+    }
+}

core-java-lang/src/test/java/com/baeldung/system/EnvironmentVariablesUnitTest.java

@@ -0,0 +1,14 @@
+package com.baeldung.system;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class EnvironmentVariablesUnitTest {
+
+    @Test
+    public void givenEnvVars_whenReadPath_thenGetValueinResult() {
+        EnvironmentVariables environmentVariables = new EnvironmentVariables();
+
+        Assert.assertNotNull(environmentVariables.getPath());
+    }
+}

core-java-lang/src/test/java/com/baeldung/system/SystemArrayCopyUnitTest.java

@@ -0,0 +1,27 @@
+package com.baeldung.system;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class SystemArrayCopyUnitTest {
+
+    @Test
+    public void givenTwoArraysAB_whenUseArrayCopy_thenArrayCopiedFromAToBInResult() {
+        int[] a = {34, 22, 44, 2, 55, 3};
+        int[] b = new int[a.length];
+
+        // copy all elements from a to b
+        System.arraycopy(a, 0, b, 0, a.length);
+        Assert.assertArrayEquals(a, b);
+    }
+
+    @Test
+    public void givenTwoArraysAB_whenUseArrayCopyPosition_thenArrayCopiedFromAToBInResult() {
+        int[] a = {34, 22, 44, 2, 55, 3};
+        int[] b = new int[a.length];
+
+        // copy 2 elements from a, starting at a[1] to b, starting at b[3]
+        System.arraycopy(a, 1, b, 3, 2);
+        Assert.assertArrayEquals(new int[] {0, 0, 0, 22, 44, 0}, b);
+    }
+}

core-java-lang/src/test/java/com/baeldung/system/SystemNanoUnitTest.java

@@ -0,0 +1,16 @@
+package com.baeldung.system;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class SystemNanoUnitTest {
+
+    @Test
+    public void givenSystem_whenCalledNanoTime_thenGivesTimeinResult() {
+        long startTime = System.nanoTime();
+        // do something that takes time
+        long endTime = System.nanoTime();
+
+        Assert.assertTrue(endTime - startTime < 10000);
+    }
+}

core-java-lang/src/test/java/com/baeldung/system/SystemPropertiesUnitTest.java

@@ -0,0 +1,56 @@
+package com.baeldung.system;
+
+import org.junit.Assert;
+import org.junit.Ignore;
+import org.junit.Test;
+
+import java.util.Properties;
+
+public class SystemPropertiesUnitTest {
+
+    @Test
+    public void givenSystem_whenCalledGetProperty_thenReturnPropertyinResult() {
+        Assert.assertNotNull(System.getProperty("java.vm.vendor"));
+    }
+
+    @Test
+    public void givenSystem_whenCalledSetProperty_thenSetPropertyasResult() {
+
+        // set a particular property
+        System.setProperty("abckey", "abcvaluefoo");
+        Assert.assertEquals("abcvaluefoo", System.getProperty("abckey"));
+    }
+
+    @Test
+    public void givenSystem_whenCalledClearProperty_thenDeletePropertyasResult() {
+
+        // Delete a property
+        System.clearProperty("abckey");
+        Assert.assertNull(System.getProperty("abckey"));
+    }
+
+    @Test
+    public void givenSystem_whenCalledGetPropertyDefaultValue_thenReturnPropertyinResult() {
+
+        System.clearProperty("dbHost");
+        String myKey = System.getProperty("dbHost", "db.host.com");
+        Assert.assertEquals("db.host.com", myKey);
+    }
+
+    @Test
+    public void givenSystem_whenCalledGetProperties_thenReturnPropertiesinResult() {
+        Properties properties = System.getProperties();
+
+        Assert.assertNotNull(properties);
+    }
+
+    @Test
+    @Ignore
+    public void givenSystem_whenCalledClearProperties_thenDeleteAllPropertiesasResult() {
+
+        // Clears all system properties. Use with care!
+        System.getProperties().clear();
+
+        Assert.assertTrue(System.getProperties().isEmpty());
+    }
+}

core-java-lang/src/test/java/com/baeldung/typeerasure/TypeErasureUnitTest.java

@@ -0,0 +1,21 @@
+package com.baeldung.typeerasure;
+
+import org.junit.Test;
+
+public class TypeErasureUnitTest {
+
+    @Test(expected = ClassCastException.class)
+    public void givenIntegerStack_whenStringPushedAndAssignPoppedValueToInteger_shouldFail() {
+        IntegerStack integerStack = new IntegerStack(5);
+        Stack stack = integerStack;
+        stack.push("Hello");
+        Integer data = integerStack.pop();
+    }
+
+    @Test
+    public void givenAnyArray_whenInvokedPrintArray_shouldSucceed() {
+        Integer[] scores = new Integer[] { 100, 200, 10, 99, 20 };
+        ArrayContentPrintUtil.printArray(scores);
+    }
+
+}