Java 8 Lambdas limitations: closures

Suppose we want to create a simple thread that only prints something on the console:

int answer = 42;
Thread t = new Thread(
  () -> System.out.println("The answer is: " + answer)
);

What if we changed the value of answer while the thread is executing?

In this article, I would like to answer this question, discussing the limitations of Java lambda expressions and consequences along the way.

The short answer is that Java implements closures, but there are limitations when we compare them with other languages. On the other hand, these limitations can be considered negligible.

To support this claim, I will show how closures play an essential role in a famous language as JavaScript.

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Convert a SID to String with Java

A security identifier (SID) is an unique identifier, commonly used in Microsoft’s systems. For example, it’s used to identify users within Windows, or, more generally, within an Active Directory.

The SID is a binary value, with a variable length, that can be also be represented as a string. This conversion is implemented by the function called ConvertSidToStringSid, provided by the library Advapi32.dll, available only in Windows.

Hence, if you need to perform this conversion, you can procede with one of these two paths:

  • Use Advapi32 (only in Windows)
  • Rewrite the conversion
Thus, it’s very useful to have that implementation in a particular language (in our case Java), to be used everywhere. I noticed that, after a research in Internet, all the implementations are wrong, despite they work in general. Therefore, I decided to write my own implementation, thoroughly tested to prove you its correctness.

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Artificial Intelligence: Markov Decision Process

In AI, sometimes, you need to plan a sequence of action that lead you to your goal. In stochastic environment, in those situation where you can’t know the outcomes of your actions, a sequence of actions is not sufficient: you need a policy.

Markov Decision Process is a mathematical framework that helps to build a policy in a stochastic environment where you know the probabilities of certain outcomes.

In this post, I give you a breif introduction of Markov Decision Process. Then, I’ll show you my implementation, in python, of the most important algorithms that can help you to find policies in stocastic enviroments. You can fine a more detailed description of the Markov Decision Process in my my slides that I’ve used for a seminar at University.

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Exif Remover with exiftool

Hi! Exif data are sometimes considered as “sensitive data”. If you want to share your photo, but you don’t want to give to companies additional information about the location where these photo where taken, or additional information about your equipment, you should remove Exif data. For this reason, I made a simple bash script that removes all Exif entries.

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Network Time Protocol request in C#

I’m writing an application in C# that needs to know if the system time is not fake (only if the network is on). For this reason, I make a class that retrieves the time from a NTP server. The class is written to prevent that the same servers are called too often using a simple circular array. For the data returned by the servers, I invite you to see the RFC-2030.

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ExitWindowsEx in C#

I post you my simple class to shutdown, reboot and logoff Windows using the famous ExitWindowsEx.

Each method is overloaded with another that force the action, in other words, it executes the action without prohibiting¬†Windows to send the WM_QUERYENDSESSION message. In this way the user can’t cancel this action.

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Hide Console Window in C#

I just made a silent application to check how much time my little brother stays on his computer. But, I needed to make an application that doesn’t show any window. Now, I show you my personal solutions to do this for the Console Application Projects and for the Windows Forms Application Projects.

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LAMP Virtual Hosts

In the last post I tell you how you can install LAMP in Ubuntu 11.10. Now I tell you how to configure virtual hosts, in this way you can create a lot of independent sites (also in different domains).

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