thank you!

I only had to complement your implementation. Although in general I prefer to avoid mutability in compile time, I haven’t found a simple way to do it that didn’t imply duplicating fields, so I chose this runtime check, which is a reasonable balance, in my opinion.

Regards,

Xavi

Please see also Xavi Miró’s great Blog entry here.

@Xavi Miró
Great idea how to ensure immutability and i appreciate that you like my implementation

yes, you’re right, this implementation can’t ensure immutability. You can use duplication of fields as Josh does, or you can complement this implementation throwing exceptions when trying to build more than once the object and when trying to modifiy the object after it’s been built. I prefer doing the latter, because I don’t like duplicating fields. I have complemented this implementation in my blog, here.

Regards,

Xavi

this is not the builder pattern. The builder pattern is used to compose a set of objects in a certain way. E.g. create a “document”, place a “title” and add a “paragraph”.

In your example you only create one singel object (not a graph of objects) and you also use one concrete type for this object.

On the first glance your example indeed looks a bit like a builder but what you do there is writing a “fancy contructor”.

A builder would work independent of the concrete object types and usually compose a graph, e.g. a document containing a title and a paragraph. The document and its nested objects then could be instances of HTMLDocumnet, HTMLTitle and HTMLParagraph in one case or RTFDocument, RTFTitle and RTFParagraph in the other case.

Code using the builder would probably look like this:
builder.start(); // get the builder ready to create a new document … alternatively create a new builder
builder.setTitle(”my title”);
builder.addParagraph(”my first paragraph”);
builder.addParagraph(”my second paragraph”);
builder.getDocument(); // construct and _compose_ a document

Usually the point where the builder is used, has no knowledge wether an RTF or an HTML document is “builded”.

Your example always knows and only can create ID3Tags … therefor it is not the builder pattern.