Pseudokode
Dette eksempel illustrerer, hvordan fabriksmetoden kan bruges til at oprette platforme-UI-elementer uden at koble klientkoden til konkrete UI-klasser.
Dialogeksemplet på tværs af platforme.
Basisdialogklassen bruger forskellige UI-elementer til at gengive sit vindue. Under forskellige operativsystemer kan disse elementer se lidt anderledes ud, men de skal stadig opføre sig konsekvent. En knap i Windows er stadig en knap i Linux.
Når fabriksmetoden kommer i spil, behøver du ikke omskrive logikken i dialogen for hvert operativsystem. Hvis vi erklærer en fabriksmetode, der producerer knapper i basisdialogklassen, kan vi senere oprette en dialogunderklasse, der returnerer Windows-stilede knapper fra fabriksmetoden. Underklassen arver derefter det meste af dialogens kode fra basisklassen, men takket være fabriksmetoden kan den gengive Windows-udseende knapper på skærmen.
For at dette mønster skal fungere, skal basedialogklassen arbejde med abstrakte knapper: en basisklasse eller en grænseflade, som alle konkrete knapper følger. På denne måde forbliver dialogens kode funktionel, uanset hvilken type knapper den fungerer med.
Selvfølgelig kan du også anvende denne tilgang til andre UI-elementer. Men med hver nye fabriksmetode, du tilføjer til dialogen, kommer du tættere på det abstrakte fabriksmønster. Frygt ikke, vi taler om dette mønster senere.
// The creator class declares the factory method that must// return an object of a product class. The creator"s subclasses// usually provide the implementation of this method.class Dialog is // The creator may also provide some default implementation // of the factory method. abstract method createButton():Button // Note that, despite its name, the creator"s primary // responsibility isn"t creating products. It usually // contains some core business logic that relies on product // objects returned by the factory method. Subclasses can // indirectly change that business logic by overriding the // factory method and returning a different type of product // from it. method render() is // Call the factory method to create a product object. Button okButton = createButton() // Now use the product. okButton.onClick(closeDialog) okButton.render()// Concrete creators override the factory method to change the// resulting product"s type.class WindowsDialog extends Dialog is method createButton():Button is return new WindowsButton()class WebDialog extends Dialog is method createButton():Button is return new HTMLButton()// The product interface declares the operations that all// concrete products must implement.interface Button is method render() method onClick(f)// Concrete products provide various implementations of the// product interface.class WindowsButton implements Button is method render(a, b) is // Render a button in Windows style. method onClick(f) is // Bind a native OS click event.class HTMLButton implements Button is method render(a, b) is // Return an HTML representation of a button. method onClick(f) is // Bind a web browser click event.class Application is field dialog: Dialog // The application picks a creator"s type depending on the // current configuration or environment settings. method initialize() is config = readApplicationConfigFile() if (config.OS == "Windows") then dialog = new WindowsDialog() else if (config.OS == "Web") then dialog = new WebDialog() else throw new Exception("Error! Unknown operating system.") // The client code works with an instance of a concrete // creator, albeit through its base interface. As long as // the client keeps working with the creator via the base // interface, you can pass it any creator"s subclass. method main() is this.initialize() dialog.render()