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SEARCH KEYWORD -- JAVA APPLICATION MAINTENANCE

  Why exception would be thrown when deleting element while looping through HashMap in Java

HashMap and other Collection types are frequently used in Java application programming. This post will explain why exception would be thrown when deleting element with Map.remove() while looping through a Map using Iterator. This issue would also occur to other Collection types such as Set, List. Below is a sample code snippet demonstrating the exception thrown. Map<String,String> map = Collections.synchronizedMap(new TreeMap<String,String>()); map.put("key1","value1"); map.put("ke...

   JAVA,HASHMAP,CONCURRENTMODIFICATIONEXCEPTION     2018-06-30 12:49:09

  What will the value of Integer.valueOf(127) == Integer.valueOf(127) be in Java?

Do you really understand how Java does the integer comparison? OK, ignore the statements in the post title. What we are interested in is another set of comparison statements. Let's first see below code snippet. public class IntegerComparison { public static void main(String[] args) { Integer a = 127, b = 127; Integer c = 128, d = 128; System.out.println(a == b); System.out.println(c == d); } } What do you think the output will be? Are they both displaying true? You will find out t...

   JAVA,==,EQUALSTO     2018-01-13 22:18:15

  A HTTPS client and HTTPS server demo in Java

In this post, I will create a HTTPS server and HTTPS client demo which can establish HTTPS communication between a server and a client using Java. This should be very useful when we want to test our understanding about SSL communication. We will use both a detailed SSL client and a simple HttpsURLConnection as the HTTPS client. Before creating the actual HTTPS server and HTTPS client, we first need to generate the keystore and truststore to be used by the server and client. To generate the keyst...

   SSL,HTTPS,JAVA,DEMO     2015-10-23 09:04:36

  Standardizing Python WSGI deployment

Over the past year I have been testing all of the new python platform as a service companies that have popped up, and I have posted my notes on my blog so that everyone can learn from my experiences. ep.io, apphosted.com, gondor.io, dotcloud.com, DjangoZoom.com, Heroku, Django hosting roundup, All and all, the platforms were very similar, they allowed you to easily host your python/django project without having to worry about managing a server or other typical system administr...

   Python,Standard,WAR,Java     2011-12-31 15:39:44

  Singleton Design Pattern in Java

Singleton is frequently used in applications where resource may be expensive to create and no instance specific state needs to be maintained. For example, when creating database connection, a singleton may be needed. Today we will share the famous Singleton design pattern in Java. 1. Definition Singleton design pattern is a design pattern that restricts the instantiation of a class to one object. It is one of the most well-known design patterns. 2. Application Singleton ...

   DESIGN PATTERN,SINGLETON,MULTITHREAD,JAVA     2020-04-11 02:16:28

  Using Java keytool programmatically

Java provides a command line tool to access and operate different keystore which store keys and certificates. This tool is named keytool and is located at \bin.  On command line, you can issue below command to generate a keystore named mytest.jks which contains a private key and certificate chain. keytool -genkeypair -alias mykey -keyalg RSA -sigalg SHA256withRSA -dname CN=Java -storetype JKS -keypass password -keystore mytest.jks -storepass password Sometimes, in testing purpose, w...

   JAVA,KEYTOOL     2016-01-09 06:28:07

  NIO vs IO in Java

Java 1.4 provides a new API for handling IO -- NIO. This is a non-blocking and buffer oriented IO API. Below are main differences between the NIO and IO in Java. IO NIO Stream oriented Buffer oriented Blocking IO Non-blocking IO N/A Using selector Stream oriented vs Buffer oriented The main difference is that IO is stream oriented where the data is read byte by byte and the data will not be buffered normally.This means there is no pointer to move forward and backward in the stream. I...

   JAVA,IO,NIO     2016-01-10 01:40:02

  JavaScript JVM runs Java

The world of software is made slightly crazy because of the huge flexibility within any computer language. Once you have absorbed the idea of a compiler written in the language it compiles what else is there left to gawp at? But... a Java Virtual Machine JVM written in JavaScript seems like another level of insanity.In fact it is a quite reasonable idea which is only made mad by the usual positions that Java, the top dog, and JavaScript the underling, usually occupy. Java is compiled not to mach...

   JavaScript,JVM,BicaVM,Cross platform,JavaScript written JVM     2011-11-22 02:51:38

  Writing unit tests for legacy code – an open letter to developers I work with

This is an email I sent today to developers who work with me, it is exactly as I wrote it except for project and developer names which I’ve redacted. Dear Developers, S asked me a difficult question today, and I think the answer (which took me a few minutes to arrive at) is worth sharing with all developers, mainly because many of you will surely face the exact same problem especially in [maintenance and enhancement] projects. By now I think it is crystal clear that one of our non-ne...

   Unit testing,Open letter     2012-02-09 05:39:56

  Hey, you may be happy to know these mottos about programming languages

Different programming are similar in helping people build staff work as people want them to. But they all have their own features which differentiate them from other programming languages. The language type may be different, for example Java is OOP, some may have different syntax. A programming motto usually can best describe the characteristic of the programming language. For example, "Write once Run everywhere" for Java. But today we are going to take a look at "unofficial mottos" about some p...

   motto,programming language     2014-04-05 20:02:13

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