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 …
Java object Serialization is an API provided by Java Library stack as a means to serialize Java objects. Serialization is a process to convert objects into a writable byte stream. Once converted into a byte-stream, these objects can be written to a file. The reverse process of this is called de-serialization. A Java object is …
In this article, we will show you a few ways to join a Java Array. Apache Commons Lang – ArrayUtils Java API Java 8 Stream 1. Apache Commons Lang – ArrayUtils The simplest way is add the Apache Commons Lang library, and use ArrayUtils. addAll to join arrays. This method supports both primitive and object …
This article shows you the difference between Mutable and Immutable objects in Java 1. Mutable object – You can change the states and fields after the object is created. For examples: StringBuilder, java.util.Date and etc. 2. Immutable object – You cannot change anything after the object is created. For examples: String, boxed primitive objects like …
In this article, we will show you a few ways to print a Java Array. Table of contents. 1. JDK 1.5 Arrays.toString 2. Java 8 Stream APIs 3. Java 8 Stream APIs – Collectors.joining 4. Jackson APIs 5. References 1. JDK 1.5 Arrays.toString We can use Arrays.toString to print a simple array and Arrays.deepToString for …
RMI stands for Remote Method Invocation and it is the object-oriented equivalent of RPC (Remote Procedure Calls). RMI was designed to make the interaction between applications using the object-oriented model and run on different machines seem like that of stand-alone programs. The code below will give you the basis to Java RMI with a very …
In this tutorial, we will show you how to install Oracle JDK 8 On Debian, manually. Environment : Debian 7 OpenJDK 1.7 is installed. (Switch to Oracle JDK 8 later) At the time of writing, OpenJDK 1.8 is not included in the default apt-get repository yet. I just don’t like the default apt repository schedule, …
In Java, the System.getenv() returns an unmodifiable string Map view of the current system environment. Map<String, String> env = System.getenv(); // get PATH environment variable String path = System.getenv("PATH"); Table of contents. 1. Get a specified environment variable 2. UnsupportedOperationException 3. Display all environment variables 4. Sort the environment variables 5. Download Source Code 6. …
In this tutorial, we will show you how to use Jackson 2.x to convert Java objects to / from a JSON. 1. Basic 1.1 Convert a Staff object to from JSON. writeValue(…) – Java Objects to JSON ObjectMapper mapper = new ObjectMapper(); // Java object to JSON file mapper.writeValue(new File("c:\\test\\staff.json"), new Staff()); // Java object …
In Java, we can use String#split() to split a string. String phone = "012-3456789"; // String#split(string regex) accepts regex as the argument String[] output = phone.split("-"); String part1 = output[0]; // 012 String part2 = output[1]; // 3456789 Table of contents 1. Split a string (default) 2. Split a string and retain the delimiter 3. …
In Java, we can use TimeUnit.SECONDS.sleep() or Thread.sleep() to delay few seconds. 1. TimeUnit JavaDelayExample.java package com.mkyong; import java.util.Date; import java.util.concurrent.TimeUnit; public class JavaDelayExample { public static void main(String[] args) { try { System.out.println("Start…" + new Date()); // delay 5 seconds TimeUnit.SECONDS.sleep(5); System.out.println("End…" + new Date()); // delay 0.5 second //TimeUnit.MICROSECONDS.sleep(500); // delay 1 minute …
In Java, you can use Map.containsKey() to check if a key exists in a Map. TestMap.java package com.mkyong.examples; import java.util.HashMap; import java.util.Map; public class TestMap { public static void main(String[] args) { Map<String, Integer> fruits = new HashMap<>(); fruits.put("apple", 1); fruits.put("orange", 2); fruits.put("banana", 3); fruits.put("watermelon", null); System.out.println("1. Is key ‘apple’ exists?"); if (fruits.containsKey("apple")) { //key …
Learn how to set the JAVA_HOME environment variable on Windows 10 or 11 with easy-to-follow steps and screenshots.
In this article, we will show you three ways to generate random integers in a range. java.util.Random.nextInt Math.random java.util.Random.ints (Java 8) 1. java.util.Random This Random().nextInt(int bound) generates a random integer from 0 (inclusive) to bound (exclusive). 1.1 Code snippet. For getRandomNumberInRange(5, 10), this will generates a random integer between 5 (inclusive) and 10 (inclusive). private …
In Java, we can use Integer.parseInt(String) to convert a String to an int; For unparsable String, it throws NumberFormatException. Integer.parseInt("1"); // ok Integer.parseInt("+1"); // ok, result = 1 Integer.parseInt("-1"); // ok, result = -1 Integer.parseInt("100"); // ok Integer.parseInt(" 1"); // NumberFormatException (contains space) Integer.parseInt("1 "); // NumberFormatException (contains space) Integer.parseInt("2147483648"); // NumberFormatException (Integer max 2,147,483,647) …
In Java, there are few ways to display double in 2 decimal places. Table of contents. 1. DecimalFormat("0.00") 2. String.format("%.2f") 3. BigDecimal 4. References Possible Duplicate How to round double / float value to 2 decimal places 1. DecimalFormat(“0.00”) We can use DecimalFormat("0.00") to ensure the number is round to 2 decimal places. DecimalExample.java package …
A simple Math.pow example, display 2 to the power of 8. In Math 2^8 = 2x2x2x2x2x2x2x2 =256 In Java Math.pow(2, 8) Note In Java, the symbol ^ is a XOR operator, DON’T use this for the power calculation. TestPower.java package com.mkyong.test; import java.text.DecimalFormat; public class TestPower { static DecimalFormat df = new DecimalFormat(".00"); public static …
A code snippet to show you how to get the number of available processors / cores / CPUs in your environment. int processors = Runtime.getRuntime().availableProcessors(); System.out.println(processors); Output 8 P.S Tested with Intel(R) Core(TM) i7-4770 CPU @3.40GHz
In this article, we will show you how to use Jsoup to check if an URL is going to redirect. 1. URL Redirection Normally, a redirect URL will return an HTTP code of 301 or 307, and the target URL will be existed in the response header “location” field. Review a sample of HTTP Response …
In this tutorial, we will show you few examples (ZonedDateTime (Java 8), Date, Calendar and Joda Time) to convert a date and time between different time zones. All examples will be converting the date and time from (UTC+8:00) Asia/Singapore – Singapore Time Date : 22-1-2015 10:15:55 AM to (UTC-5:00) America/New_York – Eastern Standard Time Date …
This Java example shows you how to display a list of TimeZone with GMT in front. P.S Tested with JDK 1.7 Java 8 You may interest at this example – Display all ZoneId and its UTC offset TimeZoneExample.java package com.mkyong.test; import java.util.TimeZone; import java.util.concurrent.TimeUnit; public class TimeZoneExample { public static void main(String[] args) { String[] …
In Java, you can use calendar.setTime(date) to convert a Date object to a Calendar object. Calendar calendar = Calendar.getInstance(); Date newDate = calendar.setTime(date); A Full example DateAndCalendar.java import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Calendar; import java.util.Date; public class DateAndCalendar { public static void main(String[] argv) throws ParseException { //1. Create a Date from String SimpleDateFormat sdf …
A code snippet to use Joda Time to convert a java.util.Date to different timezone : //java.util.Date : 22-1-2015 10:15:55 AM //System TimeZone : Asia/Singapore //Convert java.util.Date to America/New_York TimeZone DateTime dt = new DateTime(date); DateTimeZone dtZone = DateTimeZone.forID("America/New_York"); DateTime dtus = dt.withZone(dtZone); //21-1-2015 09:15:55 PM – Correct! //Convert Joda DateTime back to java.util.Date, and print …
In Java, you can use Enum valueOf() to convert a String to an Enum object, review the following case study : 1. Java Enum example WhoisRIR.java package com.mkyong.whois.utils; public enum WhoisRIR { ARIN("whois.arin.net"), RIPE("whois.ripe.net"), APNIC("whois.apnic.net"), AFRINIC("whois.afrinic.net"), LACNIC("whois.lacnic.net"), JPNIC("whois.nic.ad.jp"), KRNIC("whois.nic.or.kr"), CNNIC("ipwhois.cnnic.cn"), UNKNOWN(""); private String url; WhoisRIR(String url) { this.url = url; } public String url() { …
Quartz is good, but often times we just need a simple scheduler system to run a jar file periodically. On *unix system, you can use the build-in cron to schedule a scheduler job easily. In this example, we will show you how to create a cron job on *nix to run a jar file, by …
This article covers 3 ways to read a text file line by line : Java NIO libraries – FileChannel to read the files. It is a non-blocking mode of reading files BufferedReader – Which is a blocking operation i.e it blocks any other read/write request to the file until it has completed the task. Apache …
Normally, we are using the following ways to generate a random number in Java. 1. ThreadLocalRandom (JDK 1.7) //Generate number between 0-9 int index = ThreadLocalRandom.current().nextInt(10); 2. Random() //Generate number between 0-9 Random random = new Random(); int index = random.nextInt(10); 3. Math.random() //Generate number between 0-9 int index = (int)(Math.random()*10); Note 1. For single …
This example shows you how to use jsoup to send a search query to Google. Document doc = Jsoup .connect("https://www.google.com/search?q=mario"); .userAgent("Mozilla/5.0") .timeout(5000).get(); Unusual traffic from your computer network Don’t use this example to spam Google, you will get above message from Google, read this Google answer. 1. jsoup example Example to send a “mario” search …
In Java, we can use getResourceAsStream or getResource to read a file or multiple files from a resources folder or root of the classpath. The getResourceAsStream method returns an InputStream. // the stream holding the file content InputStream is = getClass().getClassLoader().getResourceAsStream("file.txt"); // for static access, uses the class name directly InputStream is = JavaClassName.class.getClassLoader().getResourceAsStream("file.txt"); The …
Deployed a “war” file on Tomcat, and hits following error messages : Jul 17, 2014 7:59:55 PM org.apache.catalina.loader.WebappClassLoader validateJarFile INFO: validateJarFile(D:\apache-tomcat-7.0.53\webapps\hc\WEB-INF\lib\servlet-api-2.5.jar) – jar not loaded. See Servlet Spec 3.0, section 10.7.2. Offending class: javax/servlet/Servlet.class Tools used : JDK1.7 Maven 3 Tomcat 7 1. Reason The Tomcat’s container comes with own version of servlet-api.jar, and the …
In this tutorial, we will show you how to get the nameservers of a website using Java + dig command. 1. Using Dig Command 1.1 On Linux, we can use dig command to query a DNS lookup of a website, for example : $ dig any mkyong.com //… mkyong.com. 299 IN A 162.159.x.x mkyong.com. 299 …
In this article, we will show you how to use the -XX:+PrintFlagsFinal to find out your heap size detail. In Java, the default and maximum heap size are allocated based on this – ergonomics algorithm. Heap sizes Initial heap size of 1/64 of physical memory up to 1Gbyte Maximum heap size of 1/4 of physical …
In this example, we will show you how to append values in Object[] and int[] array. Object[] obj = new Object[] { "a", "b", "c" }; ArrayList<Object> newObj = new ArrayList<Object>(Arrays.asList(obj)); newObj.add("new value"); newObj.add("new value 2"); 1. Object[] Array Example Example to append values with ArrayList : TestApp.java package com.mkyong.test; import java.util.ArrayList; import java.util.Arrays; public …
Examples show you how to convert between int[] and its’ wrapper class Integer[]. 1. Convert int[] to Integer[] public static Integer[] toObject(int[] intArray) { Integer[] result = new Integer[intArray.length]; for (int i = 0; i < intArray.length; i++) { result[i] = Integer.valueOf(intArray[i]); } return result; } 2. Convert Integer[] to int[] public static int[] toPrimitive(Integer[] …
Eclipse IDE prompts warning on new DefaultHttpClient, mark this class as deprecated. package com.mkyong.web.controller; import org.apache.http.Header; import org.apache.http.HttpResponse; import org.apache.http.client.HttpClient; import org.apache.http.client.methods.HttpGet; import org.apache.http.impl.client.DefaultHttpClient; public class WebCrawler { public static void main(String[] args) throws Exception { HttpClient client = new DefaultHttpClient(); HttpGet request = new HttpGet("https://mkyong.com"); HttpResponse response = client.execute(request); //… } } Solution Dive …
If a web request is coming from Google crawler or Google bot, the requested “user agent” should look similar like this : Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html) or (rarely used): Googlebot/2.1 (+http://www.google.com/bot.html) Source : Google crawlers 1. Java Example In Java, you can get the “user agent” from HttpServletRequest. Example : Service hosted at abcdefg.com @Autowired …
This example shows you how to get the HTTP request headers in Java. To get the HTTP request headers, you need this class HttpServletRequest : 1. HttpServletRequest Examples 1.1 Loop over the request header’s name and print out its value. WebUtils.java package com.mkyong.web.utils; import javax.servlet.http.HttpServletRequest; import java.util.Enumeration; import java.util.HashMap; import java.util.Map; public class WebUtils { …
You have been told a lot that you can’t manage memory in Java. Well, it has changed since HotSpot release of the Java VM. There is a way to directly allocate and deallocate memory as well as write and read it… Of course we are talking about the JVM memory where the Java program runs. …
In this tutorial, we will show you how to create two custom annotations – @Test and @TestInfo, to simulate a simple unit test framework. P.S This unit test example is inspired by this official Java annotation article. 1. @Test Annotation This @interface tells Java this is a custom annotation. Later, you can annotate it on …