Fluent Interfaces

A Fluent Interface is a design construct that makes your interfaces read like natural language instructions.

I kinda like how a little refactoring of method signatures can make an interface much more "interesting", shall we say ? The idea is to make the interface read more like English. So, for ex., instead of

//<>
Aggregator a = new Aggregator();
List l = dao.getfeedFromEurope();
List l1 = dao.getfeedFromAPAC();
List l2 = dao.getfeedFromAmericas();
a.aggregate(l);
a.aggregate(l1);
a.aggregate(l2);
a.setFilterPolicy(FilterPolicy.NonPayingCountries);
a.filter();
List l3 = a.getFeeds();
...

you'll write

Aggregator a = new Aggregator();
...
List l3 = a.aggregate(l).and_aggregate(l1).and_aggregate(l2).filterWith(FilterPolicy.NonPayingCountries);


Neat, isn't it? The Aggregate class methods are self-referential. In the above example, and_aggregate() just calls aggregate() internally. But the goal here is to improve readability of the interface. Of course, like everything else, fluent interfaces can be overused or misused. You can, for ex. make a very verbose interface or worse make all the interfaces fluent.

I had a difficult time explaining this construct to the code reviewers last time. I guess it takes some time getting used to this style.

The first class

The snippet below prints the first class in the stacktrace. Might be useful for logging in some situations.

public vid test ()
{
Throwable th = new Throwable();
stackTraceElement[] ste = th.getStackTrace();
System.out.println(ste[ste.length -1].getClassName());
}

I live inside Eclipse

I have a fetish for Eclipse plugins. I use

1. Mylyn for tasks management. Super-cool productivity plugin.
2. Database Development Plugin. Replaces crappy DBArtisan on my desktop. Lets me perform basic database operations easily. Lightweight and super-fast.
3. Azzuri clay Database Modelling plugin to create ER diagrams and generate DDLs from them; a basic feature that Micro$oft decided not to provide in Visio Professional edition.
4. Beyond-CVS to integrate beyond-compare (my favourite comparison tool) with Eclipse.
5. QuickREx for those esoteric regular expressions. I don't miss RegEx buddy now.
6. Remote System Explorer for connecting to linux machines and running telnet/ssh/ftp shells.
7. Eclipse web browser. Limited in features but helps during basic debugging or investigation when I want to search for an inexplicable ibatis error or how to convert dates to varchar and vice versa in the database (i always keep forgetting that). Also for keeping an eye on the latest on reddit :-). Wish it offered tabbed browsing.
   

My wish List

1. A Mind map plugin to let me gather my thoughts.
2. More powerful text editor. I use block-editing heavily.
3. A plugin for MS Outlook that lets me attach emails to Mylyn tasks.
4. A plugin for MS Excel
5. A powerful desktop indexing and search plugin.
   

Amen.

Random Thoughts

Xtreme Programming is not a synonym for planning-less programming. It is not a euphemism that poor management can hide behind.

Xtreme is an ideological change and should be a conscious decision.

Ternary logic in SQL

A fellow colleague ran into a strange problem recently with a "not-in" SQL query. There were two tables, say A and B and we weretrying to get all values of a column from table A that did not exist in Table B.

Here's a result of the queries we ran.

select count(distinct column1) from A
-----17567 records

select count(distinct column1) from B
-----10234 records

So to get the values of column1 that are in A but not in B, we tried,

select distinct column1 from A where column1 not in (select distinct column1 from B)
-----0 records

Funnily, the query returned no records. Something was wrong.

After breaking our heads for several hours on this problem, the culprit turned out to be some null values in table B.

We changed the above query as follows to make it work.

select distinct column1 from A where column1 not in (select distinct column1 from B where column1 is not null)
-----~8000 records

SQL implements what is known as ternary logic for handling NULLs. I found a lucid explanation of this problem here.