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Creating a price model using k-Nearest Neighbours + Genetic Algorithm

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Chapter 8 of Programming Collective Intelligence (PCI) explains the usage and implementation of the k-Nearest Neighbours algorithm. (k-NN). Simply put: k-NN is a classification algorithm that uses (k) for the number of neighbours to determine what class an item will belong to.  To determine the neighbours to be used the algorithm uses a distance / similarity score function, in this example (Euclidian Distance). ...

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From inside the code: Camel Routing Engine Part I

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So I’ve recently re-kindled my interest in how Apache Camel works. Camel is such a powerful integration tool and is very widely used, but anytime I put it to work, I can’t help but think “well, how the hell does it do all that!!” … guess I just have knack for not just accepting that it’s wonderful.. I want to ...

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Optional in Java 8 cheat sheet

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java.util.Optional<T> in Java 8 is a poor cousin of scala.Option[T] and Data.Maybe in Haskell. But this doesn’t mean it’s not useful. If this concept is new to you, imagine Optional as a container that may or may not contain some value. Just like all references in Java can point to some object or be null, Option may enclose some (non-null!) ...

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50 Servlet Interview Questions and Answers

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Servlets are very important topic of Java EE and all of the web applications framework such as Spring and Struts are built on top of it. This makes servlet a hot topic in Java interviews. Here I am providing a list of 50 servlet interview questions with answers to help you tackle most of the interview questions related to servlets ...

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10 More Common Mistakes Java Developers Make when Writing SQL

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I was positively surprised to see how popular my recent listing about 10 Common Mistakes Java Developers Make when Writing SQL was, both on my own blog and on my syndication partner DZone. The popularity shows a couple of things: How important SQL is to the professional Java world. How common it is to forget about some basic SQL things. How well SQL-centric ...

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Simple and lightweight pool implementation

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Object pools are containers which contain a specified amount of objects. When an object is taken from the pool, it is not available in the pool until it is put back. Objects in the pool have a lifecycle: creation, validation, destroying, etc. A pool helps to manage available resources in a better way. There are many using examples. Especially in ...

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Async Servlet Feature of Servlet 3

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Before we jump into understanding what Async Servlet is, let’s try to understand why do we need it. Let’s say we have a Servlet that takes a lot of time to process, something like below.                 LongRunningServlet.java package com.journaldev.servlet; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; ...

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5 Things You Didn’t Know About Synchronization in Java and Scala

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Practically all server applications require some sort of synchronization between multiple threads. Most of the synchronization work is done for us at the framework level, such as by our web server, DB client or messaging framework. Java and Scala provide a multitude of components to write solid multi-threaded applications. These include object pools, concurrent collections, advanced locks, execution contexts etc.. To ...

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KISS My YAGNI

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We are all familiar with the KISS (Keep It Simple, Stupid) and YAGNI (You Ain’t Gonna Need It) principles. And yet, overly complicated software is everywhere. Let’s use an application server. Definitely. We can’t go without distributed transactions. And a message queue – for the sake of decoupling. Oh, our business logic is likely to include a lot of business ...

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