In the following blog post, I would like to explain to you, the design pattern builder, why this is an algorithm in the algorithm and what advantages result from it.
General
The builder is a creational design pattern. It separates the construction of complex objects from their representations, allowing the same construction processes to be reused.
The design pattern consists of a director, the builder interface, and concrete builder implementations. The director is responsible for the abstract construction of the product and has a defined interface with the builder to pass the design instructions. The concrete builders then build the concrete product according to the instructions and can also provide the generated product.
So in the end, the director defines its own little programming language inside the program where the construction instructions can be programmed as algorithm. The builder then executes that algorithm. So we have a program in the program, an algorithm in the algorithm. Crazy!
Example cake recipe
We know such procedures from real life. For example, from the kitchen. When you bake a cake, you take your yellow mixing bowl, the ingredients, and the blue mixer and make the dough. Very concrete.
But now, if someone asks about the recipe, then we abstract it from our concrete equipment to a general manual. There, it only says you are mixing the ingredients, and your yellow mixing bowl and blue mixer are not mentioned. So someone else can bake the cake in their own kitchen with their own equipment. Should your blue mixer ever fail, you can easily carry out the recipe with a whisk or with the new food processor.
Example file generation
An example from programming is the generation of a file. For example, a pdf certificate. If you program everything directly in PDFBox, it works first. But if you ever want to use a different library, or if you also want the certificate as a normal text document or image, you need to rewrite everything.
With the design pattern, you would have an algorithm that says I want “certificate” as a title, then a dividing line, then a table and then this paragraph. Exactly how this will be implemented is not known. The PDFBox builder takes these instructions and creates the file with its own library-specific commands.
If the library or file type changes, only one new builder needs to be written. For example, a text file builder, an image builder or an OpenPDF builder. The logic of how the certificate should look at the end remains unchanged.
Conclusion
Finally, separating the construction from the production offers some advantages. The program is more expandable and modifiable. It also complies with the single responsibility principle. The disadvantage is a close coupling between the product, the concrete builder, and the classes involved in the construction, making it difficult to change the basic process.
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