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Software design patterns - Factories (Java)

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Factory Design Patterns | Java

This repository illustrates a real-world application of the factory design patterns, namely:

  • Simple Factory;
  • Factory Method, and;
  • Abstract Factory.

Each of one can be regarded an evolution of the prior.

The Problem

Scientific publications contain a bibliography section/chapter. This refers to other works that support the research or thesis. Each entry is called a citation.

There are different types of publications, e.g., books, chapters of books, journal articles. etc.

There are also different citation styles, e.g., IEEE, APA, Chicago, etc. This relates to how the citations are formatted in bibliography. Publishers require different citation styles. For example, publications on engineering, computer science and information technology may use the IEEE citation style. Natural sciences may use the APA style.

Below are examples of the IEEE citation style for three different types of publications:

Type In-text citation Formatted Citation
Book [1] D. Sarunyagate, Ed., Lasers. New York: McGraw-Hill, 1996.
Chapter in book [2] G. O. Young, "Synthetic structure of industrial plastics," in Plastics, 2nd ed., vol. 3, J. Peters, Ed. New York: McGraw-Hill, 1964, pp. 15-64.
Journal article [4] G. Liu, K. Y. Lee, and H. F. Jordan, "TDM and TWDM de Bruijn networks and shufflenets for optical communications," IEEE Trans. Comp., vol. 46, pp. 695-701, 1997.

... and for the APA style:

Type In-text citation Formatted Citation
Book (Sapolsky, 2017) Sapolsky, R. M. (2017). Behave: The biology of humans at our best and worst. Penguin Books.
Chapter in book (Dillard, 2020) Dillard, J. P. (2020). Currents in the study of persuasion. In M. B. Oliver, A. A. Raney, & J. Bryant (Eds.), Media effects: Advances in theory and research (4th ed., pp. 115–129). Routledge.
Journal article (Weinstein, 2009) Weinstein, J. (2009). “The market in Plato’s Republic.” Classical Philology, 104(4), 439-458.

You can find more information in:

Citation style classes

See javapatterns.factories.model package.

The package contains:

  • Citation interface, supertype for all concrete citation styles.

  • IEEE citation styles:

    • IEEEBookCitation, IEEEBookChapterCitation and IEEEJournalCitation.

  • APA citation styles:

    • APABookCitation, APABookChapterCitation and APAJournalCitation.

Each implementation of Citation is responsible for producing the correct format of the citation style.

Simple Factory

See javapatterns.factories.variants.simplefactory package.

The simple factory pattern describes a static method with a conditional statement that creates the required concrete product by the caller:

public class IEEECitationStyleFactory {
    /**
     * Allows the creation of a citation.
     * <p>
     * The supported types and required arguments are detailed bellow:
     * <ul>
     * <li> Book.
     *      <b>Type:</b> book
     *      <b>Args:</b> author, title, place, publisher, year
     * </li>
     * <li> Book Chapter.
     *      <b>Type:</b> bookchapter
     *      <b>Args:</b> author, title, book_title, editor, place, publisher, page_numbers, year
     * </li>
     * <li> Journal.
     *      <b>Type:</b> journal
     *      <b>Args:</b> author, title, journal_title, volume_issue, page_numbers, year
     * </li>
     * </ul>
     * </p>
     * @param type type of publication
     * @param args list of arguments according to publication type
     * @return a citation instance.
     */    
    public static Citation create(String type, String... args) {
        switch(type.toLowerCase()) {
            case "book":
                return new IEEEBookCitation(args[0], args[1], args[2], args[3], args[4]);
            case "bookchapter":
                return new IEEEBookChapterCitation(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7]);
            case "journal":
                return new IEEEJournalCitation(args[0], args[1], args[2], args[3], args[4], args[5]);
            default:
                throw new UnsupportedOperationException("Type not supported: " + type);
        }
    }
}

Documentation is of utmost importance for the caller to be aware on how to use the factory.

The client then uses the provided static method to create the required products, e.g.,:

public class MainSimpleFactory {

    public static void main(String[] args) {

        List<Citation> bibliography = new ArrayList<>();

        Citation citation1 = IEEECitationStyleFactory.create("book", "D. Sarunyagate", "Lasers",
                "New York", "McGraw-Hill", "1996");

        Citation citation2 = IEEECitationStyleFactory.create("bookchapter", "G. O. Young",
                "Synthetic structure of industrial plastics", "Plastics, 2nd ed",
                "J. Peters", "New York", "McGraw-Hill", "15-64", "1996");

        Citation citation3 = IEEECitationStyleFactory.create("journal", "G. Liu, K. Y. Lee, and H. F. Jordan",
                "TDM and TWDM de Bruijn networks and shufflenets for optical communications",
                "EEE Trans. Comp.", "46", "695-701", "1997");

        bibliography.add( citation1 );
        bibliography.add( citation2 );
        bibliography.add( citation3 );

        for(Citation c : bibliography) {
            System.out.println(c.toStringFormatted());
        }
    }
}

Note that this code is bound to the IEEECitationStyleFactory and only allows for this family of citations. Hence, this pattern can be used when you only have one family of concrete products.

The output for this program is the following:

D. Sarunyagate, Lasers, New York: McGraw-Hill, 1996.
G. O. Young, "Synthetic structure of industrial plastics" in Plastics, 2nd ed, J. Peters, Ed. New York: McGraw-Hill, 1996, pp. 15-64.
G. Liu, K. Y. Lee, and H. F. Jordan, "TDM and TWDM de Bruijn networks and shufflenets for optical communications", EEE Trans. Comp., vol. 46, pp. 695-701, 1997.

Factory Method

See javapatterns.factories.variants.factorymethod package.

This pattern is an evolution of the previous; it allows to "change" the family of concrete products, e.g., between IEEE and APA.

This is achieved by making the client use a factory interface and provide different concrete implementations of the factory (one for each family):

public interface CitationStyleFactory {
    /* javadoc ommited (the same presented earlier) */
    Citation create(String type, String ... args);
}

Whithin this pattern, the factory for the IEEE citation style factory is an implementation of the CitationStyleFactory interface:

public class IEEECitationStyleFactory implements CitationStyleFactory {
    @Override
    public Citation create(String type, String... args) {
        switch(type.toLowerCase()) {
            case "book":
                return new IEEEBookCitation(args[0], args[1], args[2], args[3], args[4]);
            case "bookchapter":
                return new IEEEBookChapterCitation(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7]);
            case "journal":
                return new IEEEJournalCitation(args[0], args[1], args[2], args[3], args[4], args[5]);
            default:
                throw new UnsupportedOperationException("Type not supported: " + type);
        }
    }
}

Finally, the client only uses the interface of the factory and products; if the factory changes, the client code stays the same:

public class MainFactoryMethod {

    public static void main(String[] args) {

        CitationStyleFactory factory = new IEEECitationStyleFactory();
        //CitationStyleFactory factory = new APACitationStyleFactory();

        List<Citation> bibliography = new ArrayList<>();

        Citation citation1 = factory.create("book", "D. Sarunyagate", "Lasers",
                "New York", "McGraw-Hill", "1996");

        Citation citation2 = factory.create("bookchapter", "G. O. Young",
                "Synthetic structure of industrial plastics", "Plastics, 2nd ed",
                "J. Peters", "New York", "McGraw-Hill", "15-64", "1996");

        Citation citation3 = factory.create("journal", "G. Liu, K. Y. Lee, and H. F. Jordan",
                "TDM and TWDM de Bruijn networks and shufflenets for optical communications",
                "EEE Trans. Comp.", "46", "695-701", "1997");

        bibliography.add( citation1 );
        bibliography.add( citation2 );
        bibliography.add( citation3 );

        for(Citation c : bibliography) {
            System.out.println(c.toStringFormatted());
        }
    }
}

This also allows to easily extend the existing code with aditional citation styles.

Abstract Factory

The abstract factory is yet another evolution of the previous pattern. In this pattern the factory can produce "related" products.

This is again achieved by the client using only interfaces (note that an abstract class can also be considered an "interface").

In this application we introduce the BibiographyManager abstract class, from which IEEEBibliographyManager and APABibliographyManager extend. Each of the later are responsible for the output of a set of formatted citations according to the in-text citation style, e.g., for IEEE:

[1] D. Sarunyagate, Lasers, New York: McGraw-Hill, 1996.

Hence, the abstract factory interface is changed to the following:

public interface CitationStyleFactory {

    /* javadoc ommited (the same presented earlier) */
    Citation createCitation(String type, String ... args);

    BibliographyManager createManager();
}

Only the method names changed to make it clear what each method produces.

The usage of the factory can, hereby, be the following:

public class MainAbstractFactory {

    public static void main(String[] args) {

        CitationStyleFactory factory = new IEEECitationStyleFactory();
        //CitationStyleFactory factory = new APACitationStyleFactory();

        Citation citation1 = factory.createCitation("book", "D. Sarunyagate", "Lasers",
                "New York", "McGraw-Hill", "1996");

        Citation citation2 = factory.createCitation("bookchapter", "G. O. Young",
                "Synthetic structure of industrial plastics", "Plastics, 2nd ed",
                "J. Peters", "New York", "McGraw-Hill", "15-64", "1996");

        Citation citation3 = factory.createCitation("journal", "G. Liu, K. Y. Lee, and H. F. Jordan",
                "TDM and TWDM de Bruijn networks and shufflenets for optical communications",
                "EEE Trans. Comp.", "46", "695-701", "1997");

        BibliographyManager bibliography = factory.createManager();

        bibliography.add( citation1 );
        bibliography.add( citation2 );
        bibliography.add( citation3 );

        System.out.println(bibliography.output());
    }
}

Exercises

There is some missing code, that you should produce, namely:

  1. The implementation of toStringFormatted() in APABookCitation, APABookChapterCitation and APAJournalCitation.Use the following citation formatting:

    • Book: [author] ([year]). [title]. [publisher].

    • Book chapter: [author] ([year]). [title]. In [editor] (Eds.), [book_title]. (pp. [pages]). [publisher].

    • Journal: [author] ([year]). "[title]." [journal_title], [volume_issue], [pages].

  2. The implementation of IEEECitationStyleFactory.getManager() and the corresponding concrete product, i.e., IEEEBibliographyManager.

  3. Run the examples by exchanging the instantiated factories.

Solutions are provided here.

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Software design patterns - Factories (Java)

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