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  How MySQL optmizes ORDER BY

In some situations, MySQL will just use an index to fulfill the requirement of an ORDER BY or GROUP BY statement without extra sorting. Although ORDER BY will not have the exact match with index, index can still be used as long as the portion that is not included in the index is included in the where clause. The following queries will all use index to process the ORDER BY or GROUP BY part: SELECT * FROM t1 ORDER BY key_part1,key_part2,... ;SELECT * FROM t1 WHERE key_part1=constant ORDER BY key_p...

   MySQL,index,ORDER BY,optimization     2012-11-13 11:01:05

  I don’t like the Ruby 1.9 hash syntax

There, I said it, I don’t like it. And I don’t know why you do either. I assume you like it anyway, everyone else I talk to seems to. My heart sank over and over again whilst I was at the recent RailsConf and saw respected rubyist after respected rubyist using the new Ruby 1.9 hash syntax in their presentations. I just don’t get it. But I’m not one to just moan. I plan to justify my feelings. Then maybe you can tell me why you do like it? My friend the hash rocket I ...

   Ruby,1.9,Hash,Feature     2011-12-14 07:05:09

  Why accessing Java HashMap may cause infinite loop in concurrent environment

HashMap in Java is frequently used to handle key/value pairs. But it is not a good candidate to be used in concurrent environment where ConcurrentHashMap should be used instead. If used in concurrent environment, it may cause lots of unexpected behavior even including make the program getting into an infinite loop situation. To understand how this can happen, let's first discuss how HaspMap works internally. In this post we will use implementation of HashMap before Java 8 as example, Java 8 prov...

   JAVA,HASHMAP,INFINITE LOOP     2020-03-29 01:47:00

  Different types of keystore in Java -- Windows-MY

Windows-MY is a type of keystore on Windows which is managed by the Windows operating system. It stores the user keys and certificates which can be used to perform cryptographic operations such as signature verification, data encryption etc. Since it's a kind of native keystore, Java doesn't have a general API to access it. To help Java applications access the keys and certificates stored in Windows-MY keystore, Java provides a separate API -- SunMSCAPI. The SunMSCAPI provider is ...

   JAVA,KEYSTORE,WINDOWS-MY,SUNMSCAPI     2016-01-09 05:45:59

  JSON unmarshal in GoLang

In almost all mainstream programming languages, there is either built-in or third-party library to support parse JSON data because it is so popular for organizing and transferring data among different services. In GoLang, the built in json package also provides functions for marshalling and unmarshalling JSON data. Marshalling GoLang struct to a JSON string is relatively simple, just need to call json.Marshal(), it's a bit complicated to unmarshal an arbitrary JSON string into a GoLang struct ob...

   GOLANG,JSON,UNMARSHAL,EMPTY INTERFACE     2019-11-09 21:57:30

  The Basics of jQuery

So, a while back I had an internal presentation at work about this topic. A few good friends in the community took a look at my slides, and they thought it would make a nice blog post because “there can’t be too many good posts about jQuery introduction and best-practices.” Whether this post is going to be good or not, is up to you but I’ll try to outline what jQuery is, and how you can start working with it. For most of you, this will just be a re-cap and probably...

   JavaScript,jQuery,Framework,Basic     2012-03-01 04:57:18

  How to Convert Images on Mac Finder

If you have a lot of images in different formats and you want to convert them to a common format, you can use the Mac Finder to do it easily and quickly. Here are the steps to follow: 1. Open the Finder and navigate to the folder where your images are stored. 2. Select the images that you want to convert. You can use the Shift key or the Command key to select multiple images at once. 3. Right-click on the selected images and choose Services > Preview from the context menu. This will open the ...

   MACOS,FINDER,IMAGE CONVERSION     2023-04-16 02:09:54

  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

  Signature sign/verification demo in Java

Digital signature is commonly used in areas where data authentication and integrity are required. It is extremely important to have signature while transferring sensitive data from one peer to other peers through network since there might be malicious applications or man-in-the-middle attacks which may alter the data along the way. Java provides some APIs to generate and verify digital signature. One important class is Signature.  When generating the signature, a private key needs to be pa...

   SECURITY,JAVA,SIGNATURE     2015-11-21 09:48:12

  Generate certificate in Java -- Self signed certificate

This is the first post in this series which I will show you how to generate SSL certificate in Java programmatically. Certificates are frequently used in SSL communication which requires the authentication of server to client. This is to make the client to trust that the server is actually the one it claims. Certificates are really important on the Internet. All HTTPS communications on the Internet need the server side to present their certificates signed by trusted CAs. The basic flow of a requ...

   Java,Certificate,X509     2014-07-30 07:42:18

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