The double colon is there [to fully qualify keywords][1] with your current namespace. This is intended to avoid name clashes for keywords which are meaningful for different libraries. Without fully qualified keywords you might accidentally overwrite some values in a map and break compatibility with a library.


  [1]: http://kotka.de/blog/2010/05/Did_you_know_III.html

As now documented [for Clojure](https://clojure.org/reference/reader#_literals) as well as [for ClojureScript](https://cljs.github.io/api/syntax/keyword-qualify), `::` keywords can also be used to resolve namespace aliases.  For example, `::foo/bar` will evaluate to `:clojure.core/bar` if `foo` is an alias of `clojure.core`. Reader exception is thrown if `foo` does not resolve to a namespace.

I often search documents (mainly PDFs) using Google. But when I right click the link, or just hang the mouse cursor over it. What I get is NOT the real link, but some thing long and confusing like the following:

    http://www.google.com/url?sa=t&amp;source=web&amp;cd=1&amp;ved=0CCUQFjAA&amp;url=http%3A%2F%2Fwww.marxists.org%2Freference%2Farchive%2Feinstein%2Fworks%2F1910s%2Frelative%2Frelativity.pdf&amp;ei=Fai1TZq-Acugtgenw6DqDg&amp;usg=AFQjCNFzYOTqpf68rQnuwW9K7wp39WL6Rg&amp;sig2=z4RqvOLEEJsPohBqr1ghxQ

I have no idea what this is but I know this nonsense is not what I want, I want the real link (for the one above: `http://www.marxists.org/reference/archive/einstein/works/1910s/relative/relativity.pdf`), not something with Google&#39;s intervention.

How do I get the “Real” link to file in Google search results?

&quot;Real&quot; link to file in Google search results?

I would like to get a list of files with a specific extension in a directory. In the API (Java 6), I see a method `File.listFiles(FileFilter)` which would do this.

Since I need a specific extension, I created a `FileNameExtensionFilter`. However I get a compilation error when I use `listFiles` with this. I assumed that since `FileNameExtensionFilter implements FileFilter`, I should be able to do this. Code follows:

    FileNameExtensionFilter filter = new FileNameExtensionFilter(&quot;text only&quot;,&quot;txt&quot;);
    String dir  = &quot;/users/blah/dirname&quot;;
    File f[] = (new File(dir)).listFiles(filter);

The last line shows a compilation error:

&gt; method listFiles(FileNameFilter) in type File is not applicable for arguments of type FileNameExtensionFilter

I am trying to use `listFiles(FileFilter)`, not `listFiles(FileNameFilter)`. Why does the compiler not recognize this?

This works if I write my own extension filter extending `FileFilter`. I would rather use `FileNameExtensionFilter` than write my own. What am I doing wrong?

Using File.listFiles with FileNameExtensionFilter

I understand keywords in Clojure being `:keyword`.  But what is the `::` used for? Why does it look like it has a binding?  

```clojure
user=&gt; :foo
:foo
user=&gt; ::foo
:user/foo
```


What is the :: used for in clojure?

I understand keywords in Clojure being <code>:keyword</code>. But what is the <code>::</code> used for? Why does it look like it has a binding?
<pre><code class="hljs language-ruby">user=> :foo
:foo
user=> ::foo
:user/foo
</code></pre>

How can I get the methods of a Java class from Clojure?

The intent of my question is **not** to start a flame war, but rather to determine in what circumstances each language is &quot;the best tool for the job.&quot;

I have read several books on Clojure ([Programming Clojure][1], [Practical Clojure][2], [The Joy of Clojure][3], and the Manning Early Access edition of [Clojure in Action][4]), and I think it is a fantastic language. I am currently reading [Let Over Lambda][5] which mostly deals with Common Lisp macros, and, it too, is a very interesting language.

I am **not** a Lisp expert (more of a newbie), but this family of languages fascinates me, as does functional programming, in general.

**Advantages of Clojure** (and disadvantages of &quot;others&quot;):

 - Runs on the JVM.
  - The JVM is a very stable, high-performance language environment that pretty well meets Sun&#39;s dream of &quot;Write once, run [almost] anywhere&quot;. I can write code on my Macbook Pro, compile it into an executable JAR file, and then run it on Linux and Microsoft Windows with little additional testing.

  - The (Hotspot, and other) JVM supports high-quality garbage collection and very performant just-in-time compilation and optimization. Where just a few years ago, I wrote everything that had to run fast in C, now I do not hesitate to do so in Java.

  - Standard, simple, multithreading model. Does Common Lisp have a standard multithreading package?

  - Breaks up the monotony of all those parentheses with `[]`, `{}`, and `#{}`, although Common Lisp experts will probably tell me that with reader macros, you can add those to CL.

**Disadvantages of Clojure**:

 - Runs on the JVM.
  - No tail recursion or continuations. Does Common Lisp support continuations? Scheme requires support for both, I believe.

**Advantages of Others (Common Lisp, in particular)** (and disadvantages of Clojure):

 - User-definable reader macros.

 - Other advantages?

Thoughts? Other differences?

  [1]: http://www.amazon.com/Programming-Clojure-Pragmatic-Programmers-Halloway/dp/1934356336/ref=sr_1_2?ie=UTF8&amp;qid=1305460278&amp;sr=8-2
  [2]: http://www.amazon.com/Practical-Clojure-Experts-Voice-Source/dp/1430272317/ref=sr_1_3?ie=UTF8&amp;qid=1305460278&amp;sr=8-3
  [3]: http://www.amazon.com/Joy-Clojure-Thinking-Way/dp/1935182641/ref=sr_1_1?ie=UTF8&amp;qid=1305460278&amp;sr=8-1
  [4]: http://www.amazon.com/Clojure-Action-Amit-Rathore/dp/1935182595/ref=sr_1_4?ie=UTF8&amp;qid=1305460278&amp;sr=8-4
  [5]: http://www.amazon.com/Let-Over-Lambda-Doug-Hoyte/dp/1435712757/ref=sr_1_1?ie=UTF8&amp;s=books&amp;qid=1305460578&amp;sr=8-1

Clojure vs other Lisps

We are going to write a concurrent program using Clojure, which is going to extract keywords from a huge amount of incoming mail which will be cross-checked with a database.

One of my teammates has suggested to use Erlang to write this program.

Here I want to note something that I am new to functional programming so I am in a little doubt whether clojure is a good choice for writing this program, or Erlang is more suitable. 



Concurrency model: Erlang vs Clojure

Why is the name of the language, &quot;Clojure&quot;? 

I googled a bit, asked in #clojure. So far, no luck.

Why is Clojure named Clojure

I have the following map which I want to iterate: 

    (def db {:classname &quot;com.mysql.jdbc.Driver&quot; 
             :subprotocol &quot;mysql&quot; 
             :subname &quot;//100.100.100.100:3306/clo&quot; 
             :username &quot;usr&quot; :password &quot;pwd&quot;})

I&#39;ve tried the following, but rather than printing the key and value **once**, it repeatedly prints the key and values as various combinations:

    (doseq [k (keys db) 
            v (vals db)] 
      (println (str k &quot; &quot; v)))

I came up with a solution, but Brian&#39;s (see below) are much more logical.

    (let [k (keys db) v (vals db)] 
      (do (println (apply str (interpose &quot; &quot; (interleave k v))))))

Content Type	Original Author	Original Content on Stackoverflow
Question	carinmeier	View Question on Stackoverflow
Solution 1 - Clojure	skuro	View Answer on Stackoverflow
Solution 2 - Clojure	Shaun Lebron	View Answer on Stackoverflow

What is the :: used for in clojure?

Clojure Problem Overview

Clojure Solutions

Solution 1 - Clojure

Solution 2 - Clojure

Using File.listFiles with FileNameExtensionFilter

"Real" link to file in Google search results?

Attributions