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  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

  Interview Programming Problems Done Right

Introduction Why 37signals Doesn't Hire Programmers Based on Brainteasers and my comment on HN generated a lot of responses, so much so that I'm writing this post to properly explain the essence of a good (IMHO) interview programming problem. Pascal's Triangle Pascal's Triangle is a shortcut for getting coefficients most often used binomial probability. The root element is 1. Every other element is the sum of the one or two above it (diagonally left and diagonally right). There are severa...

   Interview,Programming problem,Pascal,Triangle     2012-01-06 09:46:43

  mysql_fetch_array(),mysql_fetch_assoc() and mysql_fetch_row()

In PHP MySQL mannual. There are three functions which need to be clarified for some users who may get confused when choosing which one to use to get the result. mysql_fetch_array() : by seeting the different parameters, there are three ways to return the result set. MYSQL_ASSOC(Result set with field names as the associative indexs.It means you can use the field name as the index to get value of the specified cell). MYSQL_NUM(Result set with field names as the number indices). Or MYSQL_BOTH(...

   PHP,MySQL,resultset,comparison,mysql_fet     2011-08-05 04:53:09

  Understand Virtual DOM

With the popularity of React, the internals and implementation of Virtual DOM has becoming top discussed topic in tech communities and interviews. This post will give an introduction of Virtual DOM and how to implement a simple Virtual DOM logic. How to understand Virtual DOM In early days, front end developers would update a webpage view based on the data status change(usually after making AJAX call). But it brings performance penalties when there is frequent update as it would cause page reflo...

   JAVASCRIPT,DOM,VIRTUAL DOM     2019-12-07 23:43:04

  6 amazing HTML5 animation effects

HTML5 is rapidly developed in WEB world, it puts all kinds of pressure to browser development, but at the same time it also brings us lots of unexpected page effects. If we can use some HTML5 elements on our web apps,  we may get different user experience. However, for HTML5, there are lots of places need to improved. The following HTML5 animation effects are very attractive. 1. HTML5 mouseover image effect This HTML5 animation effect can be used in photo gallery, users can preview the...

   HTML5,Animation     2012-11-20 10:32:52

  How to let Google index AJAX contents?

There are lots of websites containing only one page now with the popularity of AJAX. The website will load different contents according to different inputs from users. This approach provides good user experience and it also helps save bandwidth, the drawback is that AJAX contents are not easy to be indexed by search engines. For example, if you have a website: http://example.com Users can see different contents with the appended # structure in the URL: http://example.com#1 http://example.com#2 h...

   AJAX,Search engine,Google,History     2013-07-16 00:47:14

  Can a === 1 && a === 2 && a === 3 be true in JavaScript?

Lots of you may be aware that there is famous interview question which asks whether a == 1 && a == 2 && a == 3 can be true in JavaScript. And the answer to this question is YES. The reason is that == will do a non-strict comparison which will evaluate a to a number and this provides the possibility of dynamically return the value when every time a is accessed. Have you ever wondered whether a === 1 && a === 2 && a === 3 can be true? At first glance, it seems this ...

   JAVASCRIPT,===,STRICT COMPARISON     2018-04-06 12:17:29

  Create Packed Indexes with MySQL

I am pretty much sure that you are aware of indexes which we are creating on database fields. Indexes are very useful to make your query search faster and improve the site performance. But the fact is that Indexes which we are creating on database tables also require some additional space on your hard disk and if you have not properly created these indexes than some t...

   MySQL,Compressed index,PACK_KEYS     2012-04-24 07:42:18

  Build your own internet search engine - Part 2

After having started to build my own internet search engine as described in a previous blog post, I now have read some papers and books about web search engine architecture and information retrieval to complete my hobby project. Here is a list of papers and books that I highly recommend to anybody who is interested in this topic: 1. Google: data structures and algorithms by Petteri Huuhka 2. The Anatomy of a Large-Scale Hypertextual Web Search Engine by the Google founde...

   Search engine,Paper,Database,Data structure     2011-12-22 08:25:59

  Android 4.0+ occupies quarter of Android market

Google updates its developer page about Android platform version market share. From the latest data, we can find Android 4.0 and above system occupy around 25% of all Android market. But Android 2.3 Gingerbread still occupies over 50% of Android market. From the above chart, Android 4.0 has 23.7% market share, the latest Android 4.1 JellyBean takes 1.8%, these two have 25.5% market share in total. But Android 2.3 Gingerbread alone still dominates the Android market, it takes 55.8% market share....

   Google,Android,Share     2012-10-02 19:22:19

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