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 […]
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) […]
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 […]
Currently my company is using IBATIS and pure SQLs as database persistence mechanism. I like SQL query very much, especially in tuning, but i do not like to write all SQL statement in Java application, it’s easy to hit typo error and what a stupid and tedious job? Finally my company has a new project […]
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 [] […]
Adapter , Adapter , Adapter ~ Actually Adapter design pattern can consider as a simple conversion program / class. It usually used to make two incompatible interfaces or classes to work together. Please review below Adapter design pattern image draw by me, a bit ugly 🙂 Case Study Company A developed a program in Java […]
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 […]
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 […]
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 […]
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. […]
