Tag Archives: INT

Beware of primitive wrappers in Java

Posted by on 20 November 2013 2 comments

A .NET developer can be tricked into thinking that, for example, Integer is the same with int in Java. This is dangerous, in particular for a C# developer, because in C# System.Int32 is absolutely equivalent to int. “int” is just an alias.

In Java there are 8 primitive data types :

  • byte (this is equivalent to sbyte in C#)
  • short (just like short / Int16 in C#)
  • int (just like int / Int32 in C#)
  • long (equivalent to long / Int64)
  • float (similar to float / Single)
  • double (similar to double / Double)
  • boolean (equivalent to bool / Boolean)
  • char (equivalent to char / Char)

Now, these primitive types are not part of the Java Type System, as you might have seen in Beginning Java for .NET developers in the slides, at page 21. These primitives (“value types”) have reference-type peers that are typically spelled the same (except int/Integer, char/Character) and just have the first letter capitalized.

Just like you should avoid comparing strings with == in Java, you should avoid declaring variables and fields of the reference-type peers, unless for a good reason.
The main danger lies in the fact that being reference types and Java not having operator overloading (see Beginning Java for .NET developers, slide 15) comparing two instances with the == operator will compare the instances and not the values.

“Oh, but you’re wrong!”, some of you might say, “I’ve written code like this and it worked!”. Code like this :

public class Main {

    public static void main(String[] args) {
        Integer i1 = 23;
        Integer i2 = 23;

        System.out.println("i1 == i2 -> " + (i1 == i2));
    }
}

Yes, it does print 

i1 == i2 -> true

It will work to values up to 127 inclusive. Just replace 23 with 128 (or higher) and see how things go. I’ll wait here.
Surprised? You shouldn’t be. This thing works because of a reason called integer caching (and there are ways to extend the interval on which it works – by default -128 up to 127 inclusive) but you shouldn’t rely on it.

Just use int where available or at least use the .intValue() method.

You might wonder what is the Integer (and the rest of the reference-type wrappers) there for? For a few things where they are needed. Once, because the generics in Java are lacking and you can’t define a generic type with primitive type(s) as type arguments. That’s right, you can’t have List. Scary? Yes, especially when coming from .NET where generics are not implemented with type erasure. So you need to say List and then watch out for reference comparison instead of value comparison, autoboxing performance loss and so on.

The other reason why you need these wrappers is because there is no nullable-types support in Java. So if you need to have a variable or a field that can store a primitive type but might also have to store a null then Integer will be better for you than int.

Just make sure you understand these implications and … be (type :P) safe!

New features for database developers in SQL Server 2012 : simpler paging, sequences and FileTables

Posted by on 13 July 2012 7 comments

TL;DR :

  • Paging got simpler and more efficient
  • Sequences have been introduced; better performance for auto-generated IDs and easier to have IDs unique across tables
  • FileTables have been introduced : building upon the FileStream feature now we can have non-transactional access to files stored in the DB as a windows share along with transactional access via T-SQL

Lengthier version :

SQL Server 2012, in my opinion does not come with earth-shaking changes but comes with performance improvements, feature improvements and a some new features.

First of all, Management Studio has the same engine as Visual Studio which means you get a nice WPF experience, better font rendering and CTRL-scroll quick zoom-in/zoom-out.

Let’s say you want to retrieve data from the database in a paged way (that means chunks of data of a requested size or smaller). Typically you would write this in SQL Server 2008 R2 or older :


DECLARE	@Offset		AS INT = 6
DECLARE @PageSize	AS INT = 5

SELECT	Id,
		Name
FROM
(
	SELECT	Id,
			Name,
			ROW_NUMBER()	OVER (ORDER BY Id)	AS	RowNumber
	FROM	Users
) UsersSelection

WHERE	UsersSelection.RowNumber >  @Offset
	AND	UsersSelection.RowNumber <= @Offset + @PageSize

In SQL Server 2012 the T-SQL syntax has been updated introducing keywords that facilitate a simpler and more efficient paging, keywords such as OFFSET, FETCH, NEXT ROWS and ONLY. A script that would retrieve the same data would be :


DECLARE	@Offset		AS INT = 6
DECLARE @PageSize	AS INT = 5

SELECT		Id,
			Name
FROM		Users
ORDER BY	Id
OFFSET		@Offset		ROWS
FETCH NEXT	@PageSize	ROWS ONLY

Observe the simpler, clearer syntax. Also, considering that the subselect has been eliminated (the subselect was required because the ROW_NUMBER column could not be addressed in the same select – for the WHERE clause), also the query cost was improved :

2008 :

2012 :

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