Topics in this issue:

• Dealing with hierarchical data in a DB easily
• FREE Cheat Sheets for Developers
• Creating UI mock-ups with this free tool
• Scala: successor to Java?
• Never write getters and setters again
• Upcoming courses for software developers

Dealing with hierarchical data in a DB easily

For example, in the DB, each employee record stores both his own ID and that of his superior.  Now, how can you find out all the superiors (direct or indirect) of a given employee? You could try:

	select e1.superior, e2.superior, ... from
		employees e1 join employees e2 on e1.superior=e2.id
		left join employees e3 on e2.superior=e3.id
		left join employees e4 on e3.superior=e4.id
		...

But this requires joining the table to an uncertain times (the max depth of the tree). Now, there is an easy way to do that: The idea is that you first create a temperary table containing the records the direct superior relationship like:

	(id, superior)
	==============
	(b, a)
	(c, a)
	(d, b)
	(e, b)

Then you join this temperary table with itself to expand it:

	(b, a)
	(c, a)
	(d, b)
	(e, b)
	(d, a)
	(e, a)

You can continue to expand it, but in this case it will return no new record, so it should stop. To implement this idea, if you DB server supports Common Table Expression, then you can create this temperary file as:

	with superiors as (
	-- initial records
	select id, superior from employees
	union all
	-- expansion
	select s1.id, s2.superior from
		superiors s1 join superiors s2 on s1.superior=s2.id
	)

Then you can use it in a query:

	select * from superiors

by Kent Tong

FREE Cheat Sheets for Developers

We are not talking about cheating during exams :p. I have a limit memory in my brain, so I always fogtets a syntax for a particialar language. Those cheat sheets really help me remind, and you could print them as reference cards. It also help us learn something new and apply our knownledge from one lanugage to another language. Those cheat sheets are quite good quality, since the authors have already published a book for those topics. If you think those cheat sheets are good, you properly consider to buy theirs book.

Save time and stay well-informed:

• Written by bestselling authors and leading experts
• Reliable information on major developer topics
• Filled with useful tips and source code examples
• PDF looks great on-screen or printed from your printer

Download them once you have registered dzone.com:

• Getting Started with Apache Wicket
• JavaServer Faces 2.0
• Core ASP.NET
• Core HTML
• PHP
• .. and up to 60 more topics here!

by Tim Ma

Creating UI mock-ups with this free tool

When planning the features with customers, sketching the proposed UI on a whiteboard is the most effective way. However, if the customer is not in the same location, and if it is just an additional little feature or a minor revision, then an alternative is to mock-up the UI on a computer and email the picture to him. This can be done with a free tool like the Pencil Project. It allows you to quickly mock-up a web-based UI or a desktop client GUI. I've used it and it worked very well. Highly recommended.

There are also extensions allowing it to mock-up Dojo or ExtJs widgets.

by Kent Tong

Scala: successor to Java?

Scala is a new language that is believed by some to be the successor to Java. It has received endorsements from James Gosling (the creator of Java) and James Strachan (the creator of Groovy). The latter even said that if he had known about Scala, he wouldn't have created Groovy!

Below are the features of Scala:

• It is statically typed.
• It compiles to standard Java byte code (so a Scala class can access a Java class/library and vice versa and as a result, investments in existing code base are not thrown away).
• It supports closures (just a piece of code that can be pass around to be executed later, like an anonymous inner class instance).
• It supports mixins (like multiple inheritance if the base classes only contain methods but not data).
• It supports functional progamming which suits the upcoming trend of distributed, parallel, multi-core computing.
• It supports type inference (it can guess the data type of variables so you don't repeat yourself).

Who is using Scala? Not many for the moment, but Twitter is one of them. There are even seven books written for it. If you have time, you may try it out and introduce to your colleagues. You might become the new technology super-star in your company in a couple of years :-) There are Scala IDE plugins for Eclipse, Netbeans and IDEA. They aren't that mature but should be usable.

by Kent Tong

Never write getters and setters again

If you use Java, you must have written countless getters and setters by now! But now by adding a jar file to your classpath, you can have the JVM add the getters and setters for you automatically using an annotation like:

	@Data
	class Foo {
		private Long id;
		private String name;
	}

How could this be done? This is implemented by a Java agent (in a jar file) which can dynamically modify the classes in the JVM.  To get this agent, get the open source Lombok project.

by Kent Tong

Upcoming courses for software developers

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