Believe it or not, Java contains Integer buffer overflow as well. I’m not sure is this the correct word to describe it or not, may be you can suggest some 🙂 OK, please take a look at below program, this program print the number of microseconds in a day. public class JavaLongOverflow { public static […]
There are many monetary values calculation in the financial or e-commerce application, and there is one question that arises for this – Should we use double or float data type to represent the monetary values? Answer: Always uses java.math.BigDecimal to represent the monetary values. 1. Double or Float? Here is an example of using double […]
In Java, you can use following methods to get time in milliseconds Date class – getTime() method Calendar class – getTimeInMillis() method TimeMilisecond.java package com.mkyong.test; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Calendar; import java.util.Date; public class TimeMilisecond { public static void main(String[] argv) throws ParseException { SimpleDateFormat sdf = new SimpleDateFormat("dd-M-yyyy hh:mm:ss"); String dateInString = "22-01-2015 […]
In Java, you can use the following ways to measure elapsed time in Java. 1. System.nanoTime() This is the recommended solution to measure elapsed time in Java. ExecutionTime1.java package com.mkyong.time; import java.util.concurrent.TimeUnit; public class ExecutionTime1 { public static void main(String[] args) throws InterruptedException { //start long lStartTime = System.nanoTime(); //task calculation(); //end long lEndTime = […]
Regular expression pattern in Java always is the best method to validate an user’s phone number. Here i provide a regex pattern to determines if the phone number is in correct format, the pattern force starting with 3 digits follow by a “-” and 7 digits at the end. \\d{3}-\\d{7} Explanation \\d = only digit […]
Here i show you four ways to loop a List in Java. Iterator loop For loop For loop (Adcance) While loop package com.mkyong.core; import java.util.Arrays; import java.util.Iterator; import java.util.List; public class ArrayToList { public static void main(String[] argv) { String sArray[] = new String[] { "Array 1", "Array 2", "Array 3" }; // convert array […]
Java example to show you how to convert a Array to a List ArrayToList.java package com.mkyong; import java.util.ArrayList; import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; public class ArrayToList { public static void main(String[] argv) { String sArray[] = new String[] { "A", "B", "C" }; // convert array to list #1 List<String> list = Arrays.asList(sArray); System.out.println(list); […]
Node This article is using the endTime – startTime method to measure the performance of a loop, it ignores the JVM warm up optimization, the result may not consistent or accurately. A better way is using the OpenJDK JMH framework to do the benchmark testing, because it will take care of the JVM warm up […]
Node This article is using the endTime – startTime method to measure the performance of a loop, it ignores the JVM warm up optimization, the result may not consistent or accurately. A better way is using the OpenJDK JMH framework to do the benchmark testing, because it will take care of the JVM warm up […]
I heard a lot of people talking about “Bind variables” will increase java application performance. Is this really true? i skeptical and make a simple performance test between Bind variables in PreparedStatement class and Non Bind variables in Statement class How do i test it? I will create a simple java class and keep sending […]
Problem Content Assist (Ctrl + Space) is not working in my Eclipse IDE version 3.3. I have two Eclipse IDE installed, both in my laptop and personal desktop computer. However my laptop Eclipse 3.3’s content assist feature is working perfectly, but not my personal desktop computer. Every time, when i pressed on the Ctrl + […]
Java Calendar class (java.util.Calendar) is a very useful and handy class in java date time manipulation. here i will demonstrate how to modify date time with calender class. Get current date time with Calendar() DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss"); Calendar cal = Calendar.getInstance(); System.out.println("Current Date Time : " + dateFormat.format(cal.getTime())); Calender date time manipulation […]
In Java, there are three ways to read input from a console : System.console (JDK 1.6) Scanner (JDK 1.5) BufferedReader + InputStreamReader (Classic) 1. System.console Since JDK 1.6, the developer starts to switch to the more simple and powerful java.io.Console class. JavaConsole.java package com.mkyong.io; import java.io.Console; public class JavaConsole { public static void main(String[] args) […]
This tutorial will show you how to use the Java built-in SAX parser to read and parse an XML file. 1. What is Simple API for XML (SAX) 2. Read or Parse a XML file (SAX) 3. Convert an XML file to an object 4. SAX Error Handler 5. SAX and Unicode 6. Download Source […]
This tutorial will show you how to use the Java built-in DOM parser to read an XML file. 1. What is Document Object Model (DOM) 2. Read or Parse a XML file 3. Read or Parse XML file (Unicode) 4. Parse Alexa API XML Response 5. Download Source Code 6. References Note The DOM Parser […]
Recently, I’m been asked by my colleague (C++ programmer) regarding why java does not contains a constant keyword? Actually java do contains constant function , but it just appear as different keyword – final. A final variable in java is equal to C++ constant. The final keyword is declare before a data type, it make […]
Here is another example to show how to read a file in Java with BufferedInputStream and DataInputStream classes. The readLine() from the type DataInputStream is deprecated. Sun officially announced this method can not convert property from bytes to characters. It’s advised to use BufferedReader. You may interest to read this How to read file from […]
In this article, we will show you how to use java.io.BufferedReader to read content from a file Note Read this different ways read a file 1. Files.newBufferedReader (Java 8) In Java 8, there is a new method Files.newBufferedReader(Paths.get(“file”)) to return a BufferedReader filename.txt A B C D E FileExample1.java package com.mkyong; import java.io.BufferedReader; import java.io.IOException; […]
HashMap is an object that stores both key=value as a pair. This HashMap permits null values and the null key, unsynchronized and no guarantees to the order of the map. ["key","value"] = ["java","mkyong.com"] 1. HashMap Basic 1.1 Add an Item Map map = new HashMap<String, String>(); map.put("PostgreSQL", "Free Open Source Enterprise Database"); 1.2 Get an […]
Today i facing one funny problem, i need to convert a primitive long array (long[]) to an object Long[]. First I thought java JDK should provided this kind of function, however i failed to find it. I have to use a for loop to convert it manually. Below is the covertion source code. long [] […]
Here i show a simple java example to demonstrate how to let user download a file from website. No matter you are using struts , JSP, Spring or whatever other java framework, the logic is same. 1) First we have to set HttpServletResponse response to tell browser about system going to return an application file […]
This article shows how to write data to a comma-separated values (CSV) file. Topics: OpenCSV – Write data to a CSV file Single class CSV writer – Write data to a CSV file Single class CSV writer – Unit Tests Note The RFC 4180 defines the format or definitions of a CSV file or text/csv […]
This tutorial shows you how to install OpenJDK 8, 11, 16, and other JDK builds on Ubuntu 20. 1. APT Install JDK (OpenJDK 8 and 11) 2. Install JDK manually (OpenJDK 16) 3. Install Oracle JDK on Ubuntu 4. Switch between different JDK versions 5. Add JAVA_HOME to Ubuntu environment variable 6. References 1. APT […]
Here is a brief explanation about Java Web Start from SUN “Java Web Start is a mechanism for program delivery through a standard Web server. Typically initiated through the browser, these programs are deployed to the client and executed outside the scope of the browser. Once deployed, the programs do not need to be downloaded […]
This article shows how to use regex to remove spaces in between a String. A string with spaces in between. String text = "Hello World Java."; We want to remove the spaces and display it as below: Hello World Java. 1. Java regex remove spaces In Java, we can use regex \\s+ to match whitespace […]
In Eclipse IDE, we can use Enhanced Class Decompiler plugin to decompile Java class files without source code directly. After installing and configuring the Enhanced Class Decompiler plugin, click on the class or methods, press F3, and the plugin will automatically decompile the Java class. Table of contents 1. What is Enhanced Class Decompiler plugin? […]
A very useful Java code, to open a web browser from Java application in windows or Linux. package com.mkyong; public class StartBrowser { public static void main(String args[]) { String url = "http://www.google.com"; String os = System.getProperty("os.name").toLowerCase(); Runtime rt = Runtime.getRuntime(); try{ if (os.indexOf( "win" ) >= 0) { // this doesn’t support showing urls […]
Starting a web application, but hits the following error messages : … Caused by: java.lang.ClassNotFoundException: org.apache.commons.logging.LogFactory … 1. Normal Case 1.1 Obviously, the Apache Commons logging is missing – commons-logging-xxx.jar. To fix it, get it from Maven central repository. pom.xml <dependency> <groupId>commons-logging</groupId> <artifactId>commons-logging</artifactId> <version>1.2</version> </dependency> 2. Spring Case 2.1 For Spring application, developers always excluded […]
How to install java jdk on fedora core? here i provide few steps to demonstrate how it’s work. Installation Setup 1 ) Please visit sun java website to download any java jdk version you like. http://java.sun.com/javase/downloads/index.jsp 2 ) Click download, select Linux platform, language and accept license and continue. 3 ) Select “Linux RPM in […]
This article shows a few ways to detect if an array contains a duplicated value. Java 8 Stream, compare the array size. TreeSet, compare the array size. Two for loops, classic algorithm, 0(n^2). Set, 0(n). Bitmap, boolean[] 0(n). All the above solutions are tested with the below program and generate the same output. (except 5. […]
