mkyong Java 8 examples to show you how to convert from Instant to LocalDateTime 1. Instant -> LocalDateTime The java.time.LocalDateTime has no concept of time zone, just provide a zero offset UTC+0. InstantExample1.java package com.mkyong.date; import java.time.Instant; import java.time.LocalDateTime; import java.time.ZoneOffset; public class InstantExample1 { public static void main(String[] argv) { // Parse a ISO 8601 …
A Java 8 example to display all the ZoneId and its OffSet hours and minutes. P.S Tested with Java 8 and 12 1. Display ZoneId and Offset DisplayZoneAndOffSet.java package com.mkyong; import java.time.LocalDateTime; import java.time.ZoneId; import java.time.ZoneOffset; import java.time.ZonedDateTime; import java.util.HashMap; import java.util.LinkedHashMap; import java.util.Map; public class DisplayZoneAndOffSet { public static final boolean SORT_BY_REGION = false; …
Here are a few Java examples of converting a String to the new Java 8 Date API – java.time.LocalDate DateTimeFormatter formatter = DateTimeFormatter.ofPattern("d/MM/yyyy"); String date = "16/08/2016"; //convert String to LocalDate LocalDate localDate = LocalDate.parse(date, formatter); The key is understand the DateTimeFormatter patterns Note You may interest at this classic java.util.Date example – How to …
Java 8 Stream examples to sort a Map, by keys or by values. 1. Quick Explanation Steps to sort a Map in Java 8. Convert a Map into a Stream Sort it Collect and return a new LinkedHashMap (keep the order) Map result = map.entrySet().stream() .sorted(Map.Entry.comparingByKey()) .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (oldValue, newValue) -> oldValue, LinkedHashMap::new)); P.S By …
A Java 8 example to show you how to convert a Stream to a List via Collectors.toList Java8Example1.java package com.mkyong.java8; import java.util.List; import java.util.stream.Collectors; import java.util.stream.Stream; public class Java8Example1 { public static void main(String[] args) { Stream<String> language = Stream.of("java", "python", "node"); //Convert a Stream to List List<String> result = language.collect(Collectors.toList()); result.forEach(System.out::println); } } output …
Review a Stream containing null values. Java8Examples.java package com.mkyong.java8; import java.util.List; import java.util.stream.Collectors; import java.util.stream.Stream; public class Java8Examples { public static void main(String[] args) { Stream<String> language = Stream.of("java", "python", "node", null, "ruby", null, "php"); List<String> result = language.collect(Collectors.toList()); result.forEach(System.out::println); } } output java python node null //
Few Java examples to convert a Map to a List Map<String, String> map = new HashMap<>(); // Convert all Map keys to a List List<String> result = new ArrayList(map.keySet()); // Convert all Map values to a List List<String> result2 = new ArrayList(map.values()); // Java 8, Convert all Map keys to a List List<String> result3 = …
This tutorial will show you how to back up and restore (import or export) MySQL / MariaDB database or tables. Table of contents: 1. MySQL – Backup or export databases and tables 2. MySQL – Restore or import databases and tables 3. Backup and Restore MySQL 4. References 1. MySQL – Backup or export databases …
In this tutorial, we will show you how to install Oracle JDK 8 On CentOS. Environment : CentOS 6.8 Oracle JDK 8u102 Note This guide should work on Fedora and RedHat. 1. Get Oracle JDK 8 1.1 Visit Oracle JDK download page, look for RPM version. 1.2 Copy the download link of jdk-8u102-linux-x64.rpm and wget …
In simple, mocking is creating objects that mimic the behavior of real objects. Refer to the following case study : Tested : Java 1.8 JUnit 4.12 Mockito 2.0.73-beta Mock Object Read this Wikipedia Mock object. 1. Java Examples A simple Author and Book example. 1.1 BookService to return a list of books by author name. …
In this tutorial, we will show you how to test the Spring DI components with JUnit frameworks. Technologies used : JUnit 4.12 Hamcrest 1.3 Spring 4.3.0.RELEASE Maven 1. Project Dependencies To integrate Spring with JUnit, you need spring-test.jar pom.xml <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> <exclusions> <exclusion> <groupId>org.hamcrest</groupId> <artifactId>hamcrest-core</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.hamcrest</groupId> <artifactId>hamcrest-library</artifactId> <version>1.3</version> …
In JUnit, you can organize the test cases into different categories, and run those categorized test cases with @Categories.ExcludeCategory or @Categories.IncludeCategory Note This @Categories annotation is available since JUnit 4.12 1. Category = Marker Interface In JUnit, you need to create marker interfaces to represent the categories: PerformanceTests.java package com.mkyong.category; //category marker interface public interface …
Includes hamcrest-library and test the class property and its value with hasProperty() : P.S Tested with JUnit 4.12 and hamcrest-library 1.3 ClassPropertyTest.java package com.mkyong; import org.junit.Test; import java.util.Arrays; import java.util.List; import static org.hamcrest.CoreMatchers.is; import static org.hamcrest.Matchers.containsInAnyOrder; import static org.hamcrest.Matchers.hasProperty; import static org.junit.Assert.assertThat; public class ClassPropertyTest { //Single Object @Test public void testClassProperty() { Book obj …
In Java, there are two types of exceptions – checked and unchecked exception. Here’s the summary : Checked – Extends java.lang.Exception, for recoverable condition, try-catch the exception explicitly, compile error. Unchecked – Extends java.lang.RuntimeException, for unrecoverable condition, like programming errors, no need try-catch, runtime error. 1. Custom Checked Exception Note Some popular checked exception : …
In JUnit, you can use @FixMethodOrder(MethodSorters.NAME_ASCENDING) to run the test methods by method name, in lexicographic order. P.S Tested with JUnit 4.12 ExecutionOrderTest.java package com.mkyong; import org.junit.FixMethodOrder; import org.junit.Test; import org.junit.runners.MethodSorters; import static org.hamcrest.CoreMatchers.is; import static org.junit.Assert.assertThat; //Sorts by method name @FixMethodOrder(MethodSorters.NAME_ASCENDING) public class ExecutionOrderTest { @Test public void testB() { assertThat(1 + 1, is(2)); …
The Infinitest is a continuous testing plugin, it helps to run the test automatically. 1. Install on IntelliJ 1.1 In Plugins, clicks on the “Browse repositories…” 1.2 Type “Infinitest” and clicks on the “Install” button. 1.3 Restart the Intellij IDEA. 2. Add Infinitest facet In the project structure / settings, add a “Infinitest” facet. 3. …
By default, Intellij IDEA doesn’t compile classes automatically. But, you can enable the auto compile feature by following steps : In “Project settings or preferences” Select “Build, Execution, Deployment -> Compiler” Checked Make project automatically P.S This feature is available since IDEA 12 References Brand New Compiler Mode in IntelliJ IDEA 12
Forget about JUnit assertEquals(), to test a Map, uses the more expressive IsMapContaining class from hamcrest-library.jar pom.xml <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> <exclusions> <exclusion> <groupId>org.hamcrest</groupId> <artifactId>hamcrest-core</artifactId> </exclusion> </exclusions> </dependency> <!– This will get hamcrest-core automatically –> <dependency> <groupId>org.hamcrest</groupId> <artifactId>hamcrest-library</artifactId> <version>1.3</version> <scope>test</scope> </dependency> </dependencies> 1. IsMapContaining Examples All the below assertThat checks will be passed. …
First, exclude the JUnit bundled copy of hamcrest-core, and include the useful hamcrest-library, it contains many useful methods to test the List data type. pom.xml <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> <exclusions> <exclusion> <groupId>org.hamcrest</groupId> <artifactId>hamcrest-core</artifactId> </exclusion> </exclusions> </dependency> <!– This will get hamcrest-core automatically –> <dependency> <groupId>org.hamcrest</groupId> <artifactId>hamcrest-library</artifactId> <version>1.3</version> <scope>test</scope> </dependency> </dependencies> 1. Assert List …
Try to check null value with the Hamcrest assertThat assertion, but no idea how? @Test public void testApp() { //ambiguous method call? assertThat(null, is(null)); } 1. Solution 1.1 To check null value, try is(nullValue), remember static import org.hamcrest.CoreMatchers.* //hello static import, nullValue here import static org.hamcrest.CoreMatchers.*; import org.junit.Test; //… @Test public void testApp() { //true, …
In Maven, you can declare the JUnit dependency like this: pom.xml <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> </dependency> </dependencies> But, it comes with a bundled copy of hamcrest-core library. $ mvn dependency:tree … [INFO] \- junit:junit:jar:4.12:test [INFO] \- org.hamcrest:hamcrest-core:jar:1.3:test … 1. Maven + JUnit + Hamcrest Note Not a good idea to use the default …
In Gradle, you can declare the JUnit dependency like this: build.gradle apply plugin: ‘java’ dependencies { testCompile ‘junit:junit:4.12’ } By default, JUnit comes with a bundled copy of hamcrest-core $ gradle dependencies –configuration testCompile testCompile – Compile classpath for source set ‘test’. \— junit:junit:4.12 \— org.hamcrest:hamcrest-core:1.3 1. Gradle + JUnit + Hamcrest Normally, we need …
In Logback, it is easy to set a log file name programmatically : In logback.xml, declares a variable like ${log.name} In Java, set the variable via System.setProperty(“log.name”, “abc”) 1. Full example 1.1 A logback file, we will set the ${log.name} variable later. src/main/resources/logback.xml <?xml version="1.0" encoding="UTF-8"?> <configuration> <property name="PRO_HOME" value="/home/mkyong/ant/logs" /> <property name="USER_HOME" value="${PRO_HOME}" /> …
Some MongoDB examples to show you how to perform group by, count and sort query. 1. Test Data A whois_range collection, containing many records. > db.whois_range.find(); { "_id" : 1, "country" : "us", "source" : "ARIN", "status" : "NEW", "createdDate" : ISODate("2016-05-03T08:52:32.434Z") }, { "_id" : 2, "country" : "us", "source" : "ARIN", "status" : …
Some Java reflection API examples. 1. Display all fields and data type A Java reflection example to loop over all the fields declared by a class. 1.1 A POJO. CompanyA.java package com.mkyong.test; import java.util.List; import java.util.Map; import java.util.Set; public class CompanyA { String orgName; int count; List<String> comments; Set<String> branches; Map<String, String> extra; //… } …
This article explains the Java 8 Stream.flatMap and how to use it. Topic What is flatMap? Why flat a Stream? flatMap example – Find a set of books. flatMap example – Order and LineItems. flatMap example – Splits the line by spaces. flatMap and Primitive type 1. What is flatMap()? 1.1 Review the below structure. …
In Java 8, you can either use Arrays.stream or Stream.of to convert an Array into a Stream. 1. Object Arrays For object arrays, both Arrays.stream and Stream.of returns the same output. TestJava8.java package com.mkyong.java8; import java.util.Arrays; import java.util.stream.Stream; public class TestJava8 { public static void main(String[] args) { String[] array = {"a", "b", "c", "d", …
In Java 8, Stream cannot be reused, once it is consumed or used, the stream will be closed. 1. Example – Stream is closed! Review the following example, it will throw an IllegalStateException, saying “stream is closed”. TestJava8.java package com.mkyong.java8; import java.util.Arrays; import java.util.stream.Stream; public class TestJava8 { public static void main(String[] args) { String[] …
Suddenly, my Windows 10 is unable to create new folder: In desktop or C drive, right click, then “new” -> “folder” option is disappeared!? On C drive, the top “New folder” and “New Item” icons are malfunctioning, click on it, nothing will happen? In the command prompt, the mkdir command is working fine. 1. NewFolderFix.reg …
In this article, we will show you how to use Java 8 Stream Collectors to group by, count, sum and sort a List. 1. Group By, Count and Sort 1.1 Group by a List and display the total count of it. Java8Example1.java package com.mkyong.java8; import java.util.Arrays; import java.util.List; import java.util.Map; import java.util.function.Function; import java.util.stream.Collectors; public …
In this tutorial, we will show you how to add a mapping of IP addresses to host names in the Windows Hosts file. Windows Hosts file C:\Windows\System32\drivers\etc\hosts 1. Notepad – Run as Administrator In desktop, left-bottom search box, type notepad, right click on the notepad icon and select run as administrator. 2. Edit hosts 2.1 …
Some Java examples to show you how to override equals and hashCode. 1. POJO To compare two Java objects, we need to override both equals and hashCode (Good practice). User.java public class User { private String name; private int age; private String passport; //getters and setters, constructor } User user1 = new User("mkyong", 35, "111222333"); …
Few Java 8 examples to show you how to convert a List of objects into a Map, and how to handle the duplicated keys. Hosting.java package com.mkyong.java8 public class Hosting { private int Id; private String name; private long websites; public Hosting(int id, String name, long websites) { Id = id; this.name = name; this.websites …
The Builder Pattern in Java is a creational design pattern that helps in constructing complex objects step by step. Here are three examples of the Builder pattern in Java: 1. Building a User Profile This example models a User with optional fields using the Builder Pattern. User.java package com.mkyong.builder; class User { private final String …
In Java, you can use == operator to compare Enum value. 1. Java Enum example Language.java package com.mkyong.java public enum Language { JAVA, PYTHON, NODE, NET, RUBY } 2. Compare with == Example to compare enum value with == operator. Test.java package com.mkyong.java public class Test { public static void main(String[] args) { // Covert …
This article shows a few examples of filtering a Map by its keys or values using the Java 8 stream APIs. Table of contents: 1. Java Map filter (Classic) 2. Java Map filter (Java 8) 3. Java Map filter (Java 8 Predicate) 4. References 1. Java Map filter (Classic) Before Java 8, we looped the …
While the unit test is running in the IDE, the Logback is showing a lot of configuration or status like this : 21:16:59,569 |-INFO in ch.qos.logback.classic.LoggerContext[default] – Could NOT find resource [logback.groovy] 21:16:59,569 |-INFO in ch.qos.logback.classic.LoggerContext[default] – Could NOT find resource [logback-test.xml] 21:16:59,569 |-INFO in ch.qos.logback.classic.LoggerContext[default] – Found resource [logback.xml] at … //… omitted for …
In this tutorial, we will show you few Java 8 examples to demonstrate the use of Streams filter(), collect(), findAny() and orElse() 1. Streams filter() and collect() 1.1 Before Java 8, filter a List like this : BeforeJava8.java package com.mkyong.java8; import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class BeforeJava8 { public static void main(String[] args) …
In Python, you can simply join two list with a plus + symbol like this: list1 = [1,2,3] list2 = [4,5,6] list3 = list1 + list2 print list3 #[1, 2, 3, 4, 5, 6] Note Try to compare with this Java example – how to join arrays. Python really makes join list extremely easy.
In this article, we will show you a few StringJoiner examples to join String. 1. StringJoiner 1.1 Join String by a delimiter StringJoiner sj = new StringJoiner(","); sj.add("aaa"); sj.add("bbb"); sj.add("ccc"); String result = sj.toString(); //aaa,bbb,ccc 1.2 Join String by a delimiter and starting with a supplied prefix and ending with a supplied suffix. StringJoiner sj …