# `Files.exists`

Look in the [`Files`][1] class for the static methods [`exists()`][2] and [`notExists()`][3]. Both take a [`Path`][4]. 

I guess they decided it made more sense as a [static][5] rather than instance method.


  [1]: http://docs.oracle.com/javase/8/docs/api/java/nio/file/Files.html
  [2]: http://docs.oracle.com/javase/8/docs/api/java/nio/file/Files.html#exists-java.nio.file.Path-java.nio.file.LinkOption...-
  [3]: http://docs.oracle.com/javase/8/docs/api/java/nio/file/Files.html#notExists-java.nio.file.Path-java.nio.file.LinkOption...-
  [4]: http://docs.oracle.com/javase/8/docs/api/java/nio/file/Path.html
  [5]: http://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html

I&#39;m trying to find an efficient, numerically stable algorithm to calculate a rolling variance (for instance, a variance over a 20-period rolling window). I&#39;m aware of the [Welford algorithm][1] that efficiently computes the running variance for a stream of numbers (it requires only one pass), but am not sure if this can be adapted for a rolling window. I would also like the solution to avoid the accuracy problems discussed at the top of [this article][2] by John D. Cook. A solution in any language is fine.


  [1]: http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Online_algorithm
  [2]: http://www.johndcook.com/standard_deviation.html

Rolling variance algorithm

I&#39;m developing a game for Android. It uses a surface view and uses the sort of standard 2D drawing APIs provided. When I first released the game, I was doing all sorts of daft things like re-drawing 9-patches on each frame and likewise with text. I have since optimised much of this by drawing to Bitmap objects and drawing them each frame, only re-drawing onto the Bitmap objects when required. 

I&#39;ve received complaints about battery drain before, and following my modifications I&#39;d like to know (scientifically) if I&#39;ve made any improvements. Unfortunately, I don&#39;t have any prior data to go by, so it would be most useful to compare the performance to some other game.

I&#39;ve been running Traceview, and using the results of it mostly for the purposes of identifying CPU-time-consuming methods. 

So -- **what&#39;s the best way of determining my app&#39;s battery performance, and what&#39;s a good benchmark?**

I know I can look at the %s of different apps through the settings, but this is again unscientific, as the figure I get from this also depends on what&#39;s happening in all of the other apps. I&#39;ve looked through (most of) Google&#39;s documentation, and although the message is clear that you *should* be saving battery (and it gives the occasional tip as to how), there is little indication of how I can measure how well my app is performing. The last thing I want are more complaints of battery drain in the Android Market!

Thanks in advance.

***

EDIT
----

Thanks for all your helpful advice/suggestions. What I really want to know is **how I can use the data coming from Traceview (ie: CPU time in ms spent on each frame of the game) to determine battery usage** (if this is at all possible). Reading back on my original question, I can see I was a bit vague. Thanks again.


Is my Android App Draining Battery?

Does anyone know what happened to the `path.exists()` API method in the latest Java 7 API? 
I cannot find the change in the change logs, and between b123 and b130, the method has been removed from the API.I see that there is a static `Files.exists` method but I&#39;m not sure if that is the replacement or not. 

Is anyone following the Java 7 work close enough to know how this should be handled?

Thanks for any help. 


Java 7 new IO API - Paths.exists

Does anyone know what happened to the <code>path.exists()</code> API method in the latest Java 7 API?
I cannot find the change in the change logs, and between b123 and b130, the method has been removed from the API.I see that there is a static <code>Files.exists</code> method but I'm not sure if that is the replacement or not.
Is anyone following the Java 7 work close enough to know how this should be handled?
Thanks for any help.

Please advice how to convert a `String` to `JsonObject` using `gson` library. 

What I unsuccesfully do: 

    String string = &quot;abcde&quot;;
    Gson gson = new Gson();
    JsonObject json = new JsonObject();
    json = gson.toJson(string); // Can&#39;t convert String to JsonObject

How to convert a String to JsonObject using gson library

In Java, what happens when you increment an int (or byte/short/long) beyond it&#39;s max value? Does it wrap around to the max negative value?

Does `AtomicInteger.getAndIncrement()` also behave in the same manner?

What happens when you increment an integer beyond its max value?

What is the most efficient way to remove the first 3 characters of a string?

For example:
&lt;pre&gt;
&#39;apple&#39; change to &#39;le&#39;  
&#39;a cat&#39; change to &#39;at&#39;  
&#39; a b c&#39;change to &#39;b c&#39;
&lt;/pre&gt;

Removing the first 3 characters from a string

Where should I put the log4j.properties file when using the conventional Maven directories?  

If using maven, usually you put log4j.properties under java or resources?

Can somebody please explain me why I can&#39;t cast `List&lt;&gt;` to `ArrayList&lt;&gt;` with first approach and I do with second one? Thank you.

First approach:

    ArrayList&lt;Task&gt; tmp = ((ArrayList&lt;Task&gt;)mTrackytAdapter.getAllTasks(token));

 

Second approach:

    ArrayList&lt;Task&gt; tmp = new ArrayList&lt;Task&gt;(mTrackytAdapter.getAllTasks(token));

How to cast ArrayList&lt;&gt; from List&lt;&gt;

Apologies if this has already been asked and answered; I&#39;ve looked around a bunch but haven&#39;t found exactly what I&#39;m asking.

--

1. Suppose my web app at http://example.com/ uses a private and undocumented web API at http://api.example.com/ to fetch data, e.g. via XHR or JSONP.

2. Also suppose that this web app is anonymous &amp;mdash; it does *not* require user login.

3. Since there&#39;s communication between client and server, anyone can open Fiddler, etc. to see the exact request and response, not to mention inspect the client-side JS code.

In a case like this, how can you prevent someone from using your API in a **_non-web_** client app? E.g. an iPhone app, or server-side.

To my understanding, point #2 removes the option of something like OAuth, and point #3 removes the option of e.g. API keys or even SSL.

I&#39;ve thought about things like time-based tokens or secret salts that are injected into the page on first load, but an iPhone app could easily just secretly load your webpage before making API requests.

So is there any way besides just plain obfuscation &amp;mdash; security through obscurity?

--

In case all that is too abstract, here&#39;s a simple example:

Google.com fetches its auto-complete data via some API that&#39;s private and undocumented &amp;mdash; but open on the web. What&#39;s to stop me from using it in my iPhone app?

How to prevent arbitrary client apps from using anonymous web API?

I&#39;ve been struggling to find out what is happening with this.
My scripts were working fine for a bit and suddenly half stopped.

I&#39;m accessing the api and am getting back an access token. With the access token, I can access a users public info just fine. However, when I try to post info to their FB account I get this error.

    Fatal error: Uncaught OAuthException: An active access token must be used to query information about the current user. 

Any idea what is happening here?
I&#39;m also using sessions on my site to keep track of internal user ids. Not sure if my sessions could be causing a problem.


This is my upload script where I&#39;m getting an error.

    require &#39;facebook/src/facebook.php&#39;;
    
    
    // Create our Application instance (replace this with your appId and secret).
    $facebook = new Facebook(array(
      &#39;appId&#39;  =&gt; &#39;12345678&#39;,
      &#39;secret&#39; =&gt; &#39;REMOVED&#39;,
      &#39;fileUpload&#39; =&gt; true, 
      &#39;cookie&#39; =&gt; true,
    ));
    $facebook-&gt;setFileUploadSupport(true); 
    
    $me = null;
    // Session based API call.
    if ($session) {
      try {
        $uid = $facebook-&gt;getUser();
        $me = $facebook-&gt;api(&#39;/me&#39;);
      } catch (FacebookApiException $e) {
        error_log($e);
      }
    }
    
    
    // login or logout url will be needed depending on current user state.
    if ($me) {
      $logoutUrl = $facebook-&gt;getLogoutUrl();
    } else {
      $loginUrl = $facebook-&gt;getLoginUrl();
    }
    
    
    $photo_details = array(&#39;message&#39; =&gt; &#39;my place&#39;);
    $file=&#39;photos/my.jpg&#39;; //Example image file
    $photo_details[&#39;image&#39;] = &#39;@&#39; . realpath($file);
    $upload_photo = $facebook-&gt;api(&#39;/me/photos&#39;, &#39;post&#39;, $photo_details);




facebook Uncaught OAuthException: An active access token must be used to query information about the current user

I found that I am using a deprecated method for noficitations (notification.setLatestEventInfo())

It says to use Notification.Builder. 

- **How do I use it?**

When I try to create a new instance, it tells me:

    Notification.Builder cannot be resolved to a type



How exactly to use Notification.Builder

How do you make an S3 object public via the AWS Java SDK?

Specifically, what API methods via the Java AWS SDK can be used to make an Object public when its uploaded?


How do you make an S3 object public via the aws Java SDK?

I&#39;m working on building a RESTful API for one of the applications I maintain. We&#39;re currently looking to build various things into it that require more controlled access and security. While researching how to go about securing the API, I found a few different opinions on what form to use. I&#39;ve seen some resources say HTTP-Auth is the way to go, while others prefer API keys, and even others (including the questions I found here on SO) swear by OAuth. 

Then, of course, the ones that prefer, say, API keys, say that OAuth is designed for applications getting access on behalf of a user (as I understand it, such as signing into a non-Facebook site using your Facebook account), and not for a user directly accessing resources on a site they&#39;ve specifically signed up for (such as the official Twitter client accessing the Twitter servers). However, the recommendations for OAuth seem to be even for the most basic of authentication needs.

My question, then, is - assuming it&#39;s all done over HTTPS, what are some of the practical differences between the three? When should one be considered over the others?

API Keys vs HTTP Authentication vs OAuth in a RESTful API

To `allocate()` or to `allocateDirect()`, that is the question.

For some years now I&#39;ve just stuck to the thought that since `DirectByteBuffer`s are a direct memory mapping at OS level, that it would perform quicker with get/put calls than `HeapByteBuffer`s. I never was really interested in finding out the exact details regarding the situation until now. I want to know which of the two types of `ByteBuffer`s are faster and on what conditions.

ByteBuffer.allocate() vs. ByteBuffer.allocateDirect()

For new applications written in Java 7, is there any reason to use a [`java.io.File`][2] object any more or can we consider it deprecated? 

I believe a [`java.nio.file.Path`][1] can do everything a [`java.io.File`][2] can do and more.


  [1]: http://download.oracle.com/javase/7/docs/api/java/nio/file/Path.html
  [2]: http://download.oracle.com/javase/7/docs/api/java/io/File.html

Java: Path vs File

How can I get the size of a file or directory using the new NIO in java 7?


Get file/directory size using Java 7 new IO

Java 7 introduced [java.nio.file.Path][1] as a [possible replacement][2] for java.io.File.

With File, when I access a file under a specific, I would do:

    File parent = new File(&quot;c:\\tmp&quot;);
    File child = new File(parent, &quot;child&quot;); // this accesses c:\tmp\child

What&#39;s the way to do this with Path?

I supposed this will work:

    Path parent = Paths.get(&quot;c:\\tmp&quot;);
    Path child = Paths.get(parent.toString(), &quot;child&quot;);

But calling `parent.toString()` seems ugly. Is there a better way?

  [1]: http://docs.oracle.com/javase/7/docs/api/java/nio/file/Path.html
  [2]: https://stackoverflow.com/questions/6903335/java-7-path-vs-file

How to access a sub-file/folder in Java 7 java.nio.file.Path?

WatchService looks like a great technology but its been too slow to be useful on the OS X and Linux systems I&#39;ve tested on.  To add insult to injury, it doesn&#39;t seem to get notified of all events either.

This is the case both with my own code and the canonical example from Oracle. (http://docs.oracle.com/javase/tutorial/displayCode.html?code=http://docs.oracle.com/javase/tutorial/essential/io/examples/WatchDir.java)

I recognize that the OS X OpenJDK port is unsure of this functionality (see https://wikis.oracle.com/display/OpenJDK/Mac+OS+X+Port+Project+Status) 

Has anyone been using this in production with success?

Content Type	Original Author	Original Content on Stackoverflow
Question	Eugen	View Question on Stackoverflow
Solution 1 - Java	MJB	View Answer on Stackoverflow

Java 7 new IO API - Paths.exists

Java Problem Overview

Java Solutions

Solution 1 - Java

`Files.exists`

Is my Android App Draining Battery?

Rolling variance algorithm

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