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I just had a java interview and they asked me about difference between ConcurrentHashMap and Collections.Synchronized-map and then again difference between ConcurrentHashMap and Hashtable. I didn't know so I searched the net found this java hashmap tutorial, this site has some really good java hashmap tutorial e..g how hashmap works in java, how concurrentHashmap is different than hashtable etc.

What are differences between HashSet and TreeSet in Java

Difference between JDK, JRE and JVM. Java Virtual Machine is a specification and implementaion provided by sun microsystem. It is an abstract machine that is used to provide runtime environment for java application or applet.

Difference between JDK, JRE and JVM. Java Virtual Machine is a specification and implementaion provided by sun microsystem. It is an abstract machine that is used to provide runtime environment for java application or applet.

From a technical standpoint Ext GWT and SmartGWT are quite equal apart from the fact that Smart has more to offer on the server side. Vaadin with its complete different apprach (not from the programming style but from runtime behavior) needs to be compared in a different fashion. Things like GUI responsiveness and overall performance must be carefully checked. But on the pro side you have a very small js client with vaadin which results in fast startup in the browser. On the other hand, our product is a business product and we are planing to rewrite the AdminConsole. This is something that will be used in intranets in 95% of the time. It doesnt make much of a differnece if you load 100k or 1Mb from inside the LAN.

When developing a mobile application, you need not focus on the limitations or capabilities of different browsers, as Trinidad enables you to develop applications that function properly on different browser types. The Trinidad renderer ensures that the target browser can consume contents correctly. It handles the variations in both browser implementations of HTML, JavaScript, CSS, DOM, XMLHttpRequest and system performance. For example, if a browser does not support XMLHttpRequest and is incapable of posting a partial page request to a server, support for AJAX enables the application to revert automatically to a full page submit so that the same page functions whether the browser supports XMLHttpRequest or not. Furthermore, if the target browser does no support JavaScript Trinidad will automatically render contents that work on HTML by removing all dependencies on JavaScript.

Quick guide on class, instance and local variable in Java. major difference between all these three variable is there scope and how do you access it. class variable belongs to class, instance belongs to Object and local variable belongs to local code block.

"Implementation of Units of Measurement services. A coordinates module compliant with OGC/ISO specifications for the development and deployment of geographic applications. A rigourous mapping of mathematical structures (e.g. Group, Ring, Field, VectorSpace ) to Java interfaces. A linear algebra module, which includes a first (and I believe unique) parameterized matrix class capable of resolving linear system of equations involving any kind of elements (e.g. Complex, ModuloInteger, RationalFunctions) A functions module for symbolic calculations and analysis. Different types of numbers such as real numbers of arbitrary and guaranteed precision, or the always exact rational numbers. Support for exact or arbitrary precision measurements (also strongly typed). Support for Standard , Relativistic , High-Energy , Quantum and Natural physical models. A monetary module for precision-guaranteed calculations and currencies conversions."

URL Rewriting and UrL Encoding are two similar but yet different terms and concept. URL Encoding is used to encode special character while URL Rewriting is used for Session management. this is a popular JSP interview questions .

Icefaces is an open source Ajax framework for developing RIA for the web. The applications are structured the same way as JSF applications, but with added Ajax features. In this article there will be a short description of the biggest differences between the IT Mill Toolkit 5.2.0 and Icefaces 1.6.2 based development of RIAs.

Aspect-oriented computing is continuing to increase in popularity. The modularity inherent in OSGi and Eclipse offers unique opportunities for managing and applying aspects by supplying them in bundles and directing their application to particular sets of bundles. This incubator work area is dedicated to delivering an integration of aspects and OSGi. The goal is to allow developers to use the Equinox together with AspectJ by combining the benefits of both worlds. Using a load-time weaving extension you are able to add AspectJ aspects to your bundle-based system just by putting them into general OSGi bundles. It does not matter if the pointcuts you defined inside the aspects contain join points that are defined by classes within the same bundle or any other bundle in your installation. The load-time weaving extension will take care that your aspects are woven with the appropriate classes at load-time. To illustrate this lets assume the following situation: You would like to write an aspect that traces something within the JDT plug-ins of Eclipse. Without some kind of load-time aspect weaving you would somehow need to recompile those JDT plug-ins using AJDT (for example) together with your aspect. By using the load-time aspect weaving extension all you need is to implement your aspect and add that bundle to your system. The load-time aspect weaving extension takes care of weaving your aspect with the JDT code as it is loaded. And it doesn't matter if a new JDT is installed by the user later on. The next time your application is started the load-time aspect weaving will take care of weaving your aspect into these bundles as well, if necessary. With this technology is becomes possible to modularize crosscutting concerns across different plug-ins while keeping the idea of separate compilation for bundles. Goals Provide Runtime Modularity and Versioning for Crosscutting Concerns: Aspects are used to implement crosscutting concerns. However such concerns usually compr

Aegis Software offering data integration solutions for your enterprise. We collect your enterprise data from different source and integrate them in your enterprise system or platforms through which you can increase your business performance and capabilities.

Java SE is main platform for developing application for your business. The main reason behind use of Java SE is the capability of running same code run on different types of platform. Aegis Software offering java solution for latest Java SE to their customer.

" GlassFish V3 has improved the way to front GlassFish with Apache HTTP Server. Unlike the V2 way where users had to copy tomcat-ajp.jar and commons-*.jar, you can just enable mod_jk in V3 using the network-listener's attribute "jk-enabled" without copying any additional jars into its lib directory. You can also create jk-connectors under different virtual-servers (not just default virtual-server "server" in V2) using the network-listener's "jk-enabled" attribute. "

"Since 1994, the Java programming language evolved and became a valid tool to develop reliable and performant server applications as opposed to just applets and client applications. The major disadvantage of the Java platform is that still today the only portable way to start a Java application relies on a single point of entry: the public static void main(String[]) method. Having a single-point of entry is a valid solution for client applications, where interactively a user can command to the application to quit (which can terminate the Virtual Machine process at calling the System.exit(int) method), but in those cases where the application is not interactive (server applications) there is currently no portable way to notify the Virtual Machine of its imminent shutdown. A server application written in Java might have to perform several tasks before being able to shutdown the Virtual Machine process. For example in the case of a Servlet container, before the VM process is shut down, sessions might need to be serialized to disk, and web applications need to be destroyed. One common solution to this problem is to create (for example) a ServerSocket and wait for a particular message to be issued. When the message is received, all operations required to shut down the server applications are performed and at the end the System.exit method is called to terminate the Virtual Machine process. This method however, has several disadvantages and risks: In case of a system-wide shutdown, the Virtual Machine process may be shut down directly by the operating system without notifying the running server application. If an attacker finds out the shutdown message to send to the server and discovers a way to send this message, he can easily interrupt the server's operation, bypassing all the security restrictions implemented in the operating system. Most multi-user operating systems already have a way in which server applications are started and stopped. Under Unix based

"Executing external processes from Java is a well-known problem area. It is inheriently platform dependent and requires the developer to know and test for platform specific behaviors, for example using cmd.exe on Windows or limited buffer sizes causing deadlocks. The JRE support for this is very limited, albeit better with the new Java SE 1.5 ProcessBuilder class. Reliably executing external processes can also require knowledge of the environment variables before or after the command is executed. In J2SE 1.1-1.4 there is not support for this, since the method, System.getenv(), for retriving environment variables is deprecated. There are currently several different libraries that for their own purposes have implemented frameworks around Runtime.exec() to handle the various issues outlined above. The proposed project should aim at coordinating and learning from these initatives to create and maintain a simple, reusable and well-tested package. Since some of the more problematic platforms are not readily available, it is my hope that the broad Apache community can be a great help."

"Jaxen is an open source XPath library written in Java. It is adaptable to many different object models, including DOM, XOM, dom4j, and JDOM. Is it also possible to write adapters that treat non-XML trees such as compiled Java byte code or Java beans as XML, thus enabling you to query these trees with XPath too. "

Atmosphere is a POJO based framework using Inversion of Control (IoC) to bring push/Comet and Websocket to the masses! Finally a framework which can run on any Java based Web Server, including Tomcat, Jetty, GlassFish, Weblogic, Grizzly, JBossWeb and JBoss, Resin, etc. without having to learn how Comet or WebSocket support has been differently implemented by all those Containers. The Atmosphere Framework has both client (JQuery PlugIn) and server components. Servlet 3.0 is supported along with framework like Jersey (natively), GWT (natively), Wicket, Guice, Spring etc. and programming language like JRuby, Gr oovy and Scala. We also support massive scalability with our Cluster plugin architecture (JGroups, JMS/ActiveMQ, Redis, XMPP,i etc.)

"OpenCMIS is a collection of Java libraries, frameworks and tools around the CMIS (Content Management Interoperability Services) specification. The goal of OpenCMIS is to make CMIS simple for Java client and server developers. It hides the binding details and provides APIs and SPIs on different abstraction levels. It also includes test tools for content repository developers and client application developers."

When creating a REST api with Java EE 6 and JAX-RS there comes the time when you start thinking about security. In our case we were trying to set up HTTP Basic Auth for the REST api to identify users and keep them from deleting other peoples stuff. It took me a while to understand the different aspects of configuring HTTP Basic Auth when using GlassFish:

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