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java8 August 25, 2016 1 min read by mkyong 6 comments

Java 8 – HijrahDate, How to calculate the Ramadan date

Ramadan is the 9th month of the Islamic calendar, the entire month. 1. HijrahDate -> Ramadan 2016 Full example to calculate the start and end of the Ramadan 2016 TestHijrahDate.java package com.mkyong.date; import java.time.LocalDate; import java.time.chrono.HijrahDate; import java.time.temporal.ChronoField; import java.time.temporal.TemporalAdjusters; public class TestDate { public static void main(String[] args) { //first day of Ramadan, 9th […]

java8 August 24, 2016 1 min read by mkyong 0 comments

Java 8 – MinguoDate examples

This MinguoDate calendar system is primarily used in Taiwan (Republic of China…) (ISO) 1912-01-01 = 1-01-01 (Minguo ROC) To convert the current date to the Minguo date, just subtracts the current year with number 1911, for example 2016 (ISO) – 1911 = 105 (Minguo ROC) 1. LocalDate -> MinguoDate Review a full example to convert […]

java8 August 23, 2016 4 min read by mkyong 2 comments

Java 8 – ZonedDateTime examples

Few Java 8 java.time.ZonedDateTime examples to show you how to convert a time zone between different countries. Table of contents 1. Convert LocalDateTime to ZonedDateTime 2. Malaysia (UTC+08:00) -> Japan (UTC+09:00) 3. France, Paris (UTC+02:00, DST) -> (UTC-05:00) 4. References 1. Convert LocalDateTime to ZonedDateTime The LocalDateTime has no time zone; to convert the LocalDateTime […]

java8 August 22, 2016 4 min read by mkyong 2 comments

Java 8 – Convert Date to LocalDate and LocalDateTime

Here is the code to convert java.util.Date to java.time.LocalDate. Date date = new Date(); LocalDate localDate = date.toInstant().atZone(ZoneId.systemDefault()).toLocalDate(); // different way of create instant object LocalDate localDate = Instant.ofEpochMilli(date.getTime()).atZone(ZoneId.systemDefault()).toLocalDate(); Convert java.util.Date to java.time.LocalDateTime. Date date = new Date(); LocalDateTime localDateTime = date.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime(); Convert java.util.Date to java.time.ZonedDateTime. Date date = new Date(); ZonedDateTime zonedDateTime = date.toInstant().atZone(ZoneId.systemDefault()); […]

java8 August 20, 2016 1 min read by mkyong 1 comment

Java 8 – Convert Instant to ZonedDateTime

Java 8 examples to show you how to convert from Instant to ZonedDateTime 1. Instant -> ZonedDateTime Example to convert a Instant UTC+0 to a Japan ZonedDateTime UTC+9 InstantZonedDateTime1.java package com.mkyong.date; import java.time.Instant; import java.time.ZoneId; import java.time.ZonedDateTime; public class InstantZonedDateTime1 { public static void main(String[] argv) { // Z = UTC+0 Instant instant = Instant.now(); […]

java8 August 19, 2016 1 min read by mkyong 1 comment

Java 8 – Convert Instant to LocalDateTime

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 […]

java8 August 18, 2016 7 min read by mkyong 10 comments

Java – Display all ZoneId and its UTC offset

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; […]

java8 August 16, 2016 7 min read by mkyong 25 comments

Java 8 – How to convert String to LocalDate

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 […]

java8 August 11, 2016 3 min read by mkyong 26 comments

Java 8 – How to sort a Map

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 […]

java8 August 10, 2016 1 min read by mkyong 3 comments

Java 8 – Convert a Stream to List

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 […]

java8 August 9, 2016 1 min read by mkyong 6 comments

Java 8 – Filter a null value from a Stream

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 //

java8 August 1, 2016 4 min read by mkyong 4 comments

Java 8 – Convert Map to List

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 = […]

mysql July 27, 2016 2 min read by mkyong 0 comments

How to backup and restore (import and export) MySQL database or table

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 […]

java July 22, 2016 3 min read by mkyong 7 comments

How to install Oracle JDK 8 on CentOS

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 […]

unit test June 28, 2016 7 min read by mkyong 9 comments

Unit Test – What is Mocking? and Why?

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. […]

unit test June 23, 2016 3 min read by mkyong 13 comments

JUnit + Spring integration example

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> […]

unit test June 21, 2016 3 min read by mkyong 6 comments

JUnit – Categories Test

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 […]

unit test June 15, 2016 1 min read by mkyong 0 comments

JUnit – Assert if a property exists in a class

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 […]

java June 14, 2016 3 min read by mkyong 3 comments

Java Custom Exception Examples

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 : […]

unit test June 13, 2016 1 min read by mkyong 1 comment

JUnit – Run test in a particular order

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)); […]

Intellij June 10, 2016 1 min read by mkyong 1 comment

Intellij + Infinitest Continuous Testing

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. […]

Intellij June 9, 2016 1 min read by mkyong 4 comments

Intellij IDEA – How to build project automatically

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

unit test June 8, 2016 1 min read by mkyong 1 comment

JUnit – How to test a Map

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. […]

unit test June 7, 2016 3 min read by mkyong 9 comments

JUnit – How to test a List

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 […]

unit test June 6, 2016 1 min read by mkyong 1 comment

Hamcrest – How to assertThat check null value?

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, […]

unit test May 31, 2016 1 min read by mkyong 2 comments

Maven and JUnit example

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 […]

unit test May 29, 2016 1 min read by mkyong 1 comment

Gradle and JUnit example

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 […]

logging May 7, 2016 3 min read by mkyong 4 comments

Logback – Set log file name programmatically

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}" /> […]

mongodb May 3, 2016 2 min read by mkyong 6 comments

MongoDB – group, count and sort example

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" : […]

java April 28, 2016 2 min read by mkyong 3 comments

Java – find class fields with specified data type

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; //… } […]

java8 April 14, 2016 9 min read by mkyong 10 comments

Java 8 flatMap example

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. […]

java8 April 13, 2016 3 min read by mkyong 5 comments

Java – How to convert Array to Stream

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", […]

java8 April 12, 2016 2 min read by mkyong 9 comments

Java – Stream has already been operated upon or closed

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[] […]

computer tips April 8, 2016 2 min read by mkyong 35 comments

Windows 10 – Can not create new folder

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 […]

java8 April 7, 2016 4 min read by mkyong 36 comments

Java 8 – Stream Collectors groupingBy examples

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 […]

computer tips April 6, 2016 1 min read by mkyong 2 comments

Windows 10 – Edit Hosts file

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 […]

java March 24, 2016 3 min read by mkyong 15 comments

Java – How to override equals and hashCode

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"); […]

java8 March 19, 2016 3 min read by mkyong 20 comments

Java 8 – Convert List to Map

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 […]

design pattern March 18, 2016 5 min read by mkyong 2 comments

Java Builder pattern examples

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 […]

java March 10, 2016 2 min read by mkyong 0 comments

Java – Compare Enum value

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 […]

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