Tutorials : The Anatomy Of A Groovy Builder :

The Anatomy Of A Groovy Builder

by Jon Dickinson

Groovy is a fairly recent language for the JVM, possessing a strong focus on developer productivity and literate programming (making code easier to read). In particular, the Groovy feature that enables this focus is it's builder support.

What Is a Builder?

The builder design pattern is intended to make construction of complex object graphs simpler. It does this by allowing developers to construct an object graph consistently, while providing validation that the graph is complete and structured correctly. This means, to use the screen widget example, that a screen cannot be constructed without a title, menu, or status bar, while the main content should not contain a footer element.

Builders in Java

        Navigation nav = new NavigationBuilder()
                .withItem( "Home", true, false )
                .withItem( "Admin", false, true )
                .withItem( "Logout", false, false )
                .build();

        Content content = new ContentBuilder()
                .withTable( new Table() )
                .build();

        Screen screen = new ScreenBuilder()
                .withTitle( "My Page" )
                .withNavigation( nav )
                .withContent( content )
                .withFooter(new Footer( "Our Footer text" ) )
                .build();

You can see clearly that the "Home" navigation item has focus, while the "Admin" navigation item is hidden. Unfortunately, the lines of code have almost doubled.

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