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Move articles out of core-java-lang part 2

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This commit is contained in:
catalin-burcea
2019-10-06 15:57:30 +03:00
parent 7cbe9ac12c
commit 6b80543360
43 changed files with 49 additions and 62 deletions
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68
core-java-modules/core-java-lang/src/main/java/com/baeldung/controlstructures/ConditionalBranches.java
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package com.baeldung.controlstructures;
public class ConditionalBranches {
/**
* Multiple if/else/else if statements examples. Shows different syntax usage.
*/
public static void ifElseStatementsExamples() {
int count = 2; // Initial count value.
// Basic syntax. Only one statement follows. No brace usage.
if (count > 1)
System.out.println("Count is higher than 1");
// Basic syntax. More than one statement can be included. Braces are used (recommended syntax).
if (count > 1) {
System.out.println("Count is higher than 1");
System.out.println("Count is equal to: " + count);
}
// If/Else syntax. Two different courses of action can be included.
if (count > 2) {
System.out.println("Count is higher than 2");
} else {
System.out.println("Count is lower or equal than 2");
}
// If/Else/Else If syntax. Three or more courses of action can be included.
if (count > 2) {
System.out.println("Count is higher than 2");
} else if (count <= 0) {
System.out.println("Count is less or equal than zero");
} else {
System.out.println("Count is either equal to one, or two");
}
}
/**
* Ternary Operator example.
* @see ConditionalBranches#ifElseStatementsExamples()
*/
public static void ternaryExample() {
int count = 2;
System.out.println(count > 2 ? "Count is higher than 2" : "Count is lower or equal than 2");
}
/**
* Switch structure example. Shows how to replace multiple if/else statements with one structure.
*/
public static void switchExample() {
int count = 3;
switch (count) {
case 0:
System.out.println("Count is equal to 0");
break;
case 1:
System.out.println("Count is equal to 1");
break;
case 2:
System.out.println("Count is equal to 2");
break;
default:
System.out.println("Count is either negative, or higher than 2");
break;
}
}
}

157
core-java-modules/core-java-lang/src/main/java/com/baeldung/controlstructures/Loops.java
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package com.baeldung.controlstructures;
public class Loops {
/**
* Dummy method. Only prints a generic message.
*/
private static void methodToRepeat() {
System.out.println("Dummy method.");
}
/**
* Shows how to iterate 50 times with 3 different method/control structures.
*/
public static void repetitionTo50Examples() {
for (int i = 1; i <= 50; i++) {
methodToRepeat();
}
int whileCounter = 1;
while (whileCounter <= 50) {
methodToRepeat();
whileCounter++;
}
int count = 1;
do {
methodToRepeat();
count++;
} while (count < 50);
}
/**
* Splits a sentence in words, and prints each word in a new line.
* @param sentence Sentence to print as independent words.
*/
public static void printWordByWord(String sentence) {
for (String word : sentence.split(" ")) {
System.out.println(word);
}
}
/**
* Prints text an N amount of times. Shows usage of the {@code break} branching statement.
* @param textToPrint Text to repeatedly print.
* @param times Amount to times to print received text.
*/
public static void printTextNTimes(String textToPrint, int times) {
int counter = 1;
while (true) {
System.out.println(textToPrint);
if (counter == times) {
break;
}
}
}
/**
* Prints text an N amount of times, up to 50. Shows usage of the {@code break} branching statement.
* @param textToPrint Text to repeatedly print.
* @param times Amount to times to print received text. If times is higher than 50, textToPrint will only be printed 50 times.
*/
public static void printTextNTimesUpTo50(String textToPrint, int times) {
int counter = 1;
while (counter < 50) {
System.out.println(textToPrint);
if (counter == times) {
break;
}
}
}
/**
* Finds the index of {@code name} in a list
* @param name The name to look for
* @param names The list of names
* @return The index where the name was found or -1 otherwise
*/
public static int findFirstInstanceOfName(String name, String[] names) {
int index = 0;
for ( ; index < names.length; index++) {
if (names[index].equals(name)) {
break;
}
}
return index == names.length ? -1 : index;
}
/**
* Takes several names and makes a list, skipping the specified {@code name}.
*
* @param name The name to skip
* @param names The list of names
* @return The list of names as a single string, missing the specified {@code name}.
*/
public static String makeListSkippingName(String name, String[] names) {
String list = "";
for (int i = 0; i < names.length; i++) {
if (names[i].equals(name)) {
continue;
}
list += names[i];
}
return list;
}
/**
* Prints an specified amount of even numbers. Shows usage of both {@code break} and {@code continue} branching statements.
* @param amountToPrint Amount of even numbers to print.
*/
public static void printEvenNumbers(int amountToPrint) {
if (amountToPrint <= 0) { // Invalid input
return;
}
int iterator = 0;
int amountPrinted = 0;
while (true) {
if (iterator % 2 == 0) { // Is an even number
System.out.println(iterator);
amountPrinted++;
iterator++;
} else {
iterator++;
continue; // Won't print
}
if (amountPrinted == amountToPrint) {
break;
}
}
}
/**
* Prints an specified amount of even numbers, up to 100. Shows usage of both {@code break} and {@code continue} branching statements.
* @param amountToPrint Amount of even numbers to print.
*/
public static void printEvenNumbersToAMaxOf100(int amountToPrint) {
if (amountToPrint <= 0) { // Invalid input
return;
}
int iterator = 0;
int amountPrinted = 0;
while (amountPrinted < 100) {
if (iterator % 2 == 0) { // Is an even number
System.out.println(iterator);
amountPrinted++;
iterator++;
} else {
iterator++;
continue; // Won't print
}
if (amountPrinted == amountToPrint) {
break;
}
}
}
}

10
core-java-modules/core-java-lang/src/main/java/com/baeldung/nativekeyword/DateTimeUtils.java
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package com.baeldung.nativekeyword;
public class DateTimeUtils {
public native String getSystemTime();
static {
System.loadLibrary("nativedatetimeutils");
}
}

11
core-java-modules/core-java-lang/src/main/java/com/baeldung/nativekeyword/NativeMainApp.java
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@@ -1,11 +0,0 @@
package com.baeldung.nativekeyword;
import com.baeldung.nativekeyword.DateTimeUtils;
public class NativeMainApp {
public static void main(String[] args) {
DateTimeUtils dateTimeUtils = new DateTimeUtils();
String input = dateTimeUtils.getSystemTime();
System.out.println("System time is : " + input);
}
}

22
core-java-modules/core-java-lang/src/main/java/com/baeldung/packages/TodoApp.java
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package com.baeldung.packages;
import java.time.LocalDate;
import com.baeldung.packages.domain.TodoItem;
public class TodoApp {
public static void main(String[] args) {
TodoList todoList = new TodoList();
for (int i = 0; i < 3; i++) {
TodoItem item = new TodoItem();
item.setId(Long.valueOf((long)i));
item.setDescription("Todo item " + (i + 1));
item.setDueDate(LocalDate.now().plusDays((long)(i + 1)));
todoList.addTodoItem(item);
}
todoList.getTodoItems().forEach((TodoItem todoItem) -> System.out.println(todoItem.toString()));
}
}

27
core-java-modules/core-java-lang/src/main/java/com/baeldung/packages/TodoList.java
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package com.baeldung.packages;
import java.util.ArrayList;
import java.util.List;
import com.baeldung.packages.domain.TodoItem;
public class TodoList {
private List<TodoItem> todoItems;
public void addTodoItem(TodoItem todoItem) {
if (todoItems == null) {
todoItems = new ArrayList<TodoItem>();
}
todoItems.add(todoItem);
}
public List<TodoItem> getTodoItems() {
return todoItems;
}
public void setTodoItems(List<TodoItem> todoItems) {
this.todoItems = todoItems;
}
}

39
core-java-modules/core-java-lang/src/main/java/com/baeldung/packages/domain/TodoItem.java
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package com.baeldung.packages.domain;
import java.time.LocalDate;
public class TodoItem {
private Long id;
private String description;
private LocalDate dueDate;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public LocalDate getDueDate() {
return dueDate;
}
public void setDueDate(LocalDate dueDate) {
this.dueDate = dueDate;
}
@Override
public String toString() {
return "TodoItem [id=" + id + ", description=" + description + ", dueDate=" + dueDate + "]";
}
}

14
core-java-modules/core-java-lang/src/main/java/com/baeldung/scope/BracketScopeExample.java
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package com.baeldung.scope;
public class BracketScopeExample {
public void mathOperationExample() {
Integer sum = 0;
{
Integer number = 2;
sum = sum + number;
}
// compiler error, number cannot be solved as a variable
// number++;
}
}

14
core-java-modules/core-java-lang/src/main/java/com/baeldung/scope/ClassScopeExample.java
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package com.baeldung.scope;
public class ClassScopeExample {
Integer amount = 0;
public void exampleMethod() {
amount++;
}
public void anotherExampleMethod() {
Integer anotherAmount = amount + 4;
}
}

18
core-java-modules/core-java-lang/src/main/java/com/baeldung/scope/LoopScopeExample.java
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package com.baeldung.scope;
import java.util.Arrays;
import java.util.List;
public class LoopScopeExample {
List<String> listOfNames = Arrays.asList("Joe", "Susan", "Pattrick");
public void iterationOfNames() {
String allNames = "";
for (String name : listOfNames) {
allNames = allNames + " " + name;
}
// compiler error, name cannot be resolved to a variable
// String lastNameUsed = name;
}
}

13
core-java-modules/core-java-lang/src/main/java/com/baeldung/scope/MethodScopeExample.java
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package com.baeldung.scope;
public class MethodScopeExample {
public void methodA() {
Integer area = 2;
}
public void methodB() {
// compiler error, area cannot be resolved to a variable
// area = area + 2;
}
}

12
core-java-modules/core-java-lang/src/main/java/com/baeldung/scope/NestedScopesExample.java
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package com.baeldung.scope;
public class NestedScopesExample {
String title = "Baeldung";
public void printTitle() {
System.out.println(title);
String title = "John Doe";
System.out.println(title);
}
}

17
core-java-modules/core-java-lang/src/main/java/com/baeldung/system/ChatWindow.java Normal file
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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!
}
}
}

16
core-java-modules/core-java-lang/src/main/java/com/baeldung/system/DateTimeService.java Normal file
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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();
}
}

7
core-java-modules/core-java-lang/src/main/java/com/baeldung/system/EnvironmentVariables.java Normal file
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package com.baeldung.system;
public class EnvironmentVariables {
public String getPath() {
return System.getenv("PATH");
}
}

18
core-java-modules/core-java-lang/src/main/java/com/baeldung/system/SystemErrDemo.java Normal file
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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");
}
}

24
core-java-modules/core-java-lang/src/main/java/com/baeldung/system/SystemExitDemo.java Normal file
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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()
}
}

25
core-java-modules/core-java-lang/src/main/java/com/baeldung/system/SystemOutDemo.java Normal file
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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"));
}
}

35
core-java-modules/core-java-lang/src/main/java/com/baeldung/system/UserCredentials.java Normal file
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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: ");
}
}

111
core-java-modules/core-java-lang/src/test/java/com/baeldung/compoundoperators/CompoundOperatorsUnitTest.java
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package com.baeldung.compoundoperators;
import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class CompoundOperatorsUnitTest {
@Test
public void whenAssignmentOperatorIsUsed_thenValueIsAssigned() {
int x = 5;
assertEquals(5, x);
}
@Test
public void whenCompoundAssignmentUsed_thenSameAsSimpleAssignment() {
int a = 3, b = 3, c = -2;
a = a * c; // Simple assignment operator
b *= c; // Compound assignment operator
assertEquals(a, b);
}
@Test
public void whenAssignmentOperatorIsUsed_thenValueIsReturned() {
long x = 1;
long y = (x+=2);
assertEquals(3, y);
assertEquals(y, x);
}
@Test
public void whenCompoundOperatorsAreUsed_thenOperationsArePerformedAndAssigned() {
//Simple assignment
int x = 5; //x is 5
//Incrementation
x += 5; //x is 10
assertEquals(10, x);
//Decrementation
x -= 2; //x is 8
assertEquals(8, x);
//Multiplication
x *= 2; //x is 16
assertEquals(16, x);
//Division
x /= 4; //x is 4
assertEquals(4, x);
//Modulus
x %= 3; //x is 1
assertEquals(1, x);
//Binary AND
x &= 4; //x is 0
assertEquals(0, x);
//Binary exclusive OR
x ^= 4; //x is 4
assertEquals(4, x);
//Binary inclusive OR
x |= 8; //x is 12
assertEquals(12, x);
//Binary Left Shift
x <<= 2; //x is 48
assertEquals(48, x);
//Binary Right Shift
x >>= 2; //x is 12
assertEquals(12, x);
//Shift right zero fill
x >>>= 1; //x is 6
assertEquals(6, x);
}
@Test(expected = NullPointerException.class)
public void whenArrayIsNull_thenThrowNullException() {
int[] numbers = null;
//Trying Incrementation
numbers[2] += 5;
}
@Test(expected = ArrayIndexOutOfBoundsException.class)
public void whenArrayIndexNotCorrect_thenThrowArrayIndexException() {
int[] numbers = {0, 1};
//Trying Incrementation
numbers[2] += 5;
}
@Test
public void whenArrayIndexIsCorrect_thenPerformOperation() {
int[] numbers = {0, 1};
//Incrementation
numbers[1] += 5;
assertEquals(6, numbers[1]);
}
}

27
core-java-modules/core-java-lang/src/test/java/com/baeldung/nativekeyword/DateTimeUtilsManualTest.java
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@@ -1,27 +0,0 @@
package com.baeldung.nativekeyword;
import static org.junit.Assert.assertNotNull;
import org.junit.BeforeClass;
import org.junit.Test;
import org.slf4j.Logger;
public class DateTimeUtilsManualTest {
private static final Logger LOG = org.slf4j.LoggerFactory.getLogger(DateTimeUtilsManualTest.class);
@BeforeClass
public static void setUpClass() {
System.loadLibrary("msvcr100");
System.loadLibrary("libgcc_s_sjlj-1");
System.loadLibrary("libstdc++-6");
System.loadLibrary("nativedatetimeutils");
}
@Test
public void givenNativeLibsLoaded_thenNativeMethodIsAccessible() {
DateTimeUtils dateTimeUtils = new DateTimeUtils();
LOG.info("System time is : " + dateTimeUtils.getSystemTime());
assertNotNull(dateTimeUtils.getSystemTime());
}
}

23
core-java-modules/core-java-lang/src/test/java/com/baeldung/packages/PackagesUnitTest.java
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@@ -1,23 +0,0 @@
package com.baeldung.packages;
import static org.junit.Assert.assertEquals;
import java.time.LocalDate;
import org.junit.Test;
import com.baeldung.packages.domain.TodoItem;
public class PackagesUnitTest {
@Test
public void whenTodoItemAdded_ThenSizeIncreases() {
TodoItem todoItem = new TodoItem();
todoItem.setId(1L);
todoItem.setDescription("Test the Todo List");
todoItem.setDueDate(LocalDate.now());
TodoList todoList = new TodoList();
todoList.addTodoItem(todoItem);
assertEquals(1, todoList.getTodoItems().size());
}
}

15
core-java-modules/core-java-lang/src/test/java/com/baeldung/system/DateTimeServiceUnitTest.java Normal file
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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());
}
}

14
core-java-modules/core-java-lang/src/test/java/com/baeldung/system/EnvironmentVariablesUnitTest.java Normal file
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@@ -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());
}
}

27
core-java-modules/core-java-lang/src/test/java/com/baeldung/system/SystemArrayCopyUnitTest.java Normal file
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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);
}
}

16
core-java-modules/core-java-lang/src/test/java/com/baeldung/system/SystemNanoUnitTest.java Normal file
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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);
}
}

56
core-java-modules/core-java-lang/src/test/java/com/baeldung/system/SystemPropertiesUnitTest.java Normal file
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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());
}
}