Month: February 2021

Rich Domain vs. Structs & Services

Posted on by ghyze

When joining a project, you have to work with the code that you’re given. It’s only when you start to understand the project that you can start to change the way the problems are being solved. Most projects that I’ve joined use an object oriented language, but not all projects use object oriented principles. In order to be able to discuss this issue, I’ve started to call it “Rich Domain vs Structs & Services”. Both are ways of solving problems, or of implementing the functionality that is needed. Both have their advantages, but I think that the Rich Domain is usually preferable.

Structs & Services

Structs refer to (complex) data structures, without any logic. The most common use is in C, which is a procedural language. It was a step towards an object oriented language, but it’s not a class yet since it doesn’t contain any logic. Operations on this data are handled in procedures. These procedures are replicated in object oriented services with (usually static) functions.

Rich Domain

A Rich Domain uses classes with fields and methods that operate on those fields. All domain logic is captured in those methods. Services are only used to interact with other systems or dependencies. These services are not part of the core domain, since the core domain should not have any dependencies.

The discussion

In my opinion, using Structs & Services in an object oriented language is a mistake. Not a big mistake, because you can still create clear, working programs using that pattern. It is more intuitive to separate the data and logic, and therefore it’s easier to build. But when the subject matter gets more complex, it’s easier to have a robust and flexible domain. According to Domain Driven Design, the insight that is encoded into the domain will help to evolve the domain to be more valuable. Another argument against Structs & Services is that you’ll end up having to implement a single change in multiple locations. If a struct needs another field, the service needs to make use of that field. This makes things more complicated than needed.

Boxes

Posted on by ghyze

When I started university, I told myself to save all my projects. That way I could create a library of useful bits that I could use in later projects.

That was nearly a quarter of a century ago. Since then I’ve collected a projects folder of about 20 GB. This contains lots of duplicates, special purpose projects, and code that just doesn’t run anymore. (Software rot is real!)

Over the past couple of weeks, I started to go through my projects folder. And I found this little game, appar-ently written in October/November 2012 and I forgot about it until now. It’s written in Java 1.6, but still runs in java 15.

The controls are simple: use the right and left arrow to move the blocks. Esc to quit. Don’t let the blocks pile up too high. You get points for three or more connecting blocks (diagonal doesn’t count).

Here’s the Github.

Java XML Api

Posted on by ghyze

Who uses XML in 2021? We all use JSON these days, aren’t we? Well, it turns out XML is still being used. These code fragments could help get you up to speed when you’re new to the Java XML API.

Create an empty XML document

To start from scratch, you’ll need to create an empty document:


Document doc = DocumentBuilderFactory
                .newInstance()
                .newDocumentBuilder()
                .newDocument();

Create document from existing file

To load an XML file, use the following fragment.


File source = new File("/location/of.xml");
Document doc = DocumentBuilderFactory
                    .newInstance()
                    .newDocumentBuilder()
                    .parse(target);

Add a new element

Now that we have the document, it’s time to add some elements and attributes. Note that Document and Element are both Nodes.


final Element newNode = doc.createElement(xmlElement.getName());
newNode.setAttribute(attributeName, attributeValue);
	
node.appendChild(newNode);

Get nodes matching XPath expression

XPath is a powerful way to search your XML document. Every XPath expression can match multiple nodes, or it can match none. Here’s how to use it in Java:


final String xPathExpression = "//node";
final XPath xpath = XPathFactory.newInstance().newXPath();
NodeList nodeList = (NodeList) xpath.evaluate(xPathExpression, 
        doc, 
        XPathConstants.NODESET);

JSON to XML

JSON is simpler and much more in use these days. However, it has less features than XML. Namespaces and attributes are missing, for example. Usually these aren’t needed, but they can be useful. To convert JSON to XML, you could use the org.json:json dependency. This will create an XML structure similar to the input JSON.

<properties>
	<org-json.version>20201115</org-json.version>
</properties>

<dependencies>
	<dependency>
		<groupId>org.json</groupId>
		<artifactId>json</artifactId>
		<version>${org-json.version}</version>
	</dependency>
</dependencies>


JSONObject content = new JSONObject(json);
String xmlFragment = XML.toString(content);

Writing XML

When we’re done manipulating the DOM, it’s time to write the XML to file or to a String. The following fragment does the trick


private void writeToConsole(final Document doc) 
    throws TransformerException{
	final StringWriter writer = new StringWriter();
	writeToTarget(doc, new StreamResult(writer));
	System.out.println(writer.toString());
}

private void writeToFile(final Document doc, File target) 
    throws TransformerException, IOException{
	try (final FileWriter fileWriter = new FileWriter(target)) {
		final StreamResult streamResult = new StreamResult(fileWriter);
		writeToTarget(doc, streamResult);
	}
}

private void writeToTarget(final Document doc, final StreamResult target) 
    throws TransformerException {
	final Transformer xformer = TransformerFactory.newInstance()
              .newTransformer();
	xformer.transform(new DOMSource(doc), target);
}

Can you solve this puzzle?

Posted on by ghyze

Every once in a while, I come across this little puzzle. I have no idea who made it, or what the intended answer is.

Usually there are a lot of people giving the same answer. And although that answer is reasonable, I don’t think it’s correct. When we modify the calculation to (x * y) + x, we’ll get the answers matching the question. But we’ll need to modify the calculation, and I don’t think that is needed.

Another solution would be to take the previous answer, and add the current sum.

There’s an old joke among nerds that goes like this:

There’s a hint in that joke that points to a different answer to the puzzle. You can write numbers in different ways. In computer science we use a couple of different number systems, like binary, or Base 2, which deals with the digits 0 and 1. That’s not the only system we use. There’s also octal (Base 8, digits 0 to 7) and hexadecimal (Base 16, digits 0 to 9 and A to F). And of course we still use decimal.

That joke about 10 kind of people, we can do better:

If we now go back to the puzzle, taking into account these number systems, we can arrive at a solution that doesn’t need to modify the calculation. We only need to modify the representation of the answer.

And there we have it, the answer is 13! Which is written in Base 3 as 111. There’s no need to modify the calculation. All we needed to do is change the representation of the answer.