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  <=> operator in MySQL

Have you ever seen "<=>" in a SQL query while using MySQL? Does it mean less and equals to and greater than? Actually if you consider it as the union of <= and =>, great, you are close to it. This is one form of equal operator in MySQL, it has the similar meaning to the = operator with some subtle difference. According to MySQL documentation, <=> is NULL-safe equal. This operator performs an equality comparison like the = operator, but returns 1 rather than NULL if both operand...

   MySQL,NULL safe,<=>     2014-03-24 06:23:22

  How to monitor user behavior in webpage

Sometimes there is a need for website owners to monitor user behavior on the site so that they can know what pages are mostly visited and which parts are more popular so that they can provide better service to their users. These behavior usually contain user clicks, user mouse over events etc. These data can be sent back to server when triggered with some meta data. In this post, we will cover a few ways to monitor user behavior on a web portal and send data back to backend sever. 1. Synchronous...

   HTML,BEACON API,PING,USER BEHAVIOR     2019-06-29 06:06:59

  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

  PHP to get access token for Facebook app

Since Facebook is now using OAuth 2.0 to authenticate apps to access user information. the SDK of Facebook has provided developers some useful functions to get authentication done. For example, in PHP SDK, there are getAccessToken(), getLoginUrl() etc. But unfortunately, for me I cannot use getAccessToken() method to get the user access token, it only returns me the app access token. Finally I gave up this approach to get access token for the time being. I may later retry this approach if I have...

   Faceook,PHP,Access token,signed request     2012-03-27 12:37:46

  Let's talk about JSON.stringify()

JSON has been used in lots of places to exchange data among different services/systems. Nowadays all mainstream programming languages have built-in library support of JSON data parse and stringify. In this post, let's talk about JSON.stringify() in JavaScript. Let's first take a small example of Object conversion handling. There is a requirement to convert below object const todayILearn = { _id: 1, content: '今天学习 JSON.stringify()，我很开心！', ...

   JAVASCIPT,JSON,JSON.STRINGIFY     2020-02-22 04:25:08

  Generate first N prime numbers

Recently I am taking an online course named "Startup Engineering" on coursera. There is one assignment which is to use NodeJS to write a program to generate the first 100 prime numbers. This may be very easy for many people. Here I just want to share with you the code to generate not only the first 100 prime numbers. but also any number of prime numbers. Below is the code snippet: //Helper class to generate prime numbers var PrimeProcessor=(function(){ var primeArray=[]; functio...

   Algorithm,Prime number,NodeJS,coursera,JavaScript     2013-06-29 22:08:22

  About go get and go install in Go 1.16

Go version 1.16 beta1 has been released on 18 Dec 2020, major features of Go 1.16 have been finalized with this beta release. Many people are discussing about the support of Apple M1, however, this post will not cover this topic. Instead the focus will be on go get and go install changes. There are lots of changes related to modules in Go 1.16, the details can be found in the release note. Below are some of the key highlights. GO111MODULE is on by default, if wanna keep old behavior, needs...

   GOLANG,GO 1.16,GO INSTALL     2020-12-26 00:26:58

  How to handle ES6 modules in NodeJS

In modern JavaScript, there are two types of modules: ES6 module and CommonJS module used by NodeJS. These two types of module are not compatible. Many people would wonder how to load ES6 modules in their NodeJS project. This post will show how this can be done. Difference The syntax of the module being loaded is different. CommonJS modules are loaded with require() and exported with module.exports. ES6 modules are loaded and exported using import and export respectively. Merchanismwise require(...

   NODEJS,COMMONJS,ES6     2020-08-28 22:01:33

  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

  A simple tutorial on Linux nohup command

In our daily work, there might be need to run some important program for hours or even days without being abruptly terminated. In such case, we may want to run the program with command nohup. nohup is the abbreviation of no hangup, i.e, don't hang up or terminate the process. This command will tell the process to ignore the system HUP signal. The HUP signal will be emitted when the terminal is exited or disconnected. Normally process will abort its execution when receiving this signal.  Bas...

   NOHUP,LINUX     2020-08-08 01:14:50

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