java - Why do some languages need Boxing and Unboxing? -

-

This is not a question of boxing and unblocking, rather it is like why languages ​​like Java and C # is required?

I am very familiar wtih C ++, STL and Boost.

I can write it very easily in C ++, 

  std :: vector & lt; Double & gt; Dummy;

I have some experience with Java, but I was surprised because I had to write something like this, 

  ArrayList < Double & gt; Dummy = New Arrestist & lt; Double & gt; ();

My question, why should it be an object, while talking about generic, it is very difficult to include primitive types?

In the case of Java, the reason for this is that in a generic way, Java is a compile-time move, which will give you the image Code> Aranyst & lt; String & gt; . However, Java's generics are implemented with type extinction: during normal run-time the information is lost, it was for compatibility reasons, because the generics were added for a long time in the life of Java, because of its Meaning, run-time, a ArrayList & lt; String & gt; effectively an ArrayList & lt; Object & gt; (or better: Just ArrayList returns the object in all of its methods) that when you retrieve a value, the string is entered

but since int does not get from object , you can not put it in an arrelist which you hope (At runtime) Object and you can not enter any object to int which means that the primitive int Need to get wrapped up in kind that is the object , such as Integer from.

For example, C # works differently, Generic C # also applies to runtime and list & lt; Int & gt; No boxing is required with . Boxing in C # only occurs when you try to store a value type in a variable type such as object such as int . Since int from c object to c #, written object obj = 2 is fully valid, although int will be boxed, which is done Automatically by the compiler (no integer reference type is user or nothing).


Comments

Post a Comment

Popular posts from this blog

c++ - Linux and clipboard -

-
After selecting the copies of the buffer in Linux, after the text, we can click and paste the button between the mouse. I think there is a special buffer for this, I want to use it. Programming Language: C ++ Your Library: Qt Thanks. There is just one more correct answer than Paul Dixon, which answers your needs: / P > QClipboard * clipboard = QApplication :: clipboard (); CastString Selected Text = Clipboard-> Text (QClipboard :: Selection);
Read more

Visual Studio 2005: How to speed up builds when a VSMDI is open? -

-
Using Visual Studio 2005, if I open the test in VSMFI and try to run the tests, then sometimes the projects are ready. However, they run very slow. CPU 99% waste and output window VS Shows things associated with compiling it. Is there any way to fix this? It does not make any sense. It is not necessary to upgrade that we are a viable alternative to those people who have to deal with the legacy code. Did you try to upgrade SP1? I do not know of any specific problem in this area, but this will be the first change I tried to do.
Read more

booting ubuntu from usb using virtualbox -

-
I am trying to install Ubuntu on a USB, the problem is that I do not want to repeat the boot once, I want to keep my windows, but I want to boot Ubuntu using the virtualbox and USB to the Ubuntu Want to use my hard drive, but how? The virtualbox will not recognize USB as a hard drive when installing an ISO In virtualbox, you have to create a virtual hard disk. Make a USB drive and tell the virtual box to install a virtual hard drive that you just created. EDIT: To answer some more questions: In the new Virtual Disk dialog, click the button next to the location field, click on the button Virtual Disk on Flash Drive To access, click the arrow next to Save in the Select File in the window next to Save In, and you can access your flash drive from there. I recommend setting the image to be allocated dynamically, because the size of your flash drive is not available disk space. I name the image, then select that image to install Ubuntu in the Verbill box. The virtualbox will never...
Read more