org.nakedobjects.applib.adapters
Interface Parser<T>

public interface Parser<T>

Provides a mechanism for parsing and rendering string representations of objects.

Specifically, this interface embodies three related capabilties:

• to parse a string representation and convert to an object.
• to provide a string representation of the object, for use as its title.
• to indicate the typical length of such a string representation.

For custom-written (as opposed to third-party) value types, the ability for the Parser to provide a title responsibilities overlap with other conventions for domain objects. Specifically, normally we write a title() method to return a title. In such cases a typical implementation of Parser would just delegate to the value type itself to obtain the title (ie invoking the title() method directly rather than having the framework do this).

Similarly, the ability to return a typical length also overlaps with the TypicalLength annotation; which is why TypicalLength cannot be applied to types, only to properties and parameters.

For third-party value types, eg Time-and-Money there is no ability to write title() methods or annotated with TypicalLength; so this is the main reason that this interface has to deal with titles and lengths.

This interface is used in two complementary ways:

• As one option, it allows objects to take control of their own parsing, by implementing directly. However, the instance is used as a factory for itself. The framework will instantiate an instance, invoke the appropriate method method, and use the returned object. The instantiated instance itself will be discarded.
• Alternatively, an implementor of this interface can be nominated in the Parseable annotation, allowing a class that needs to be parseable to indicate how it can be parsed.

Whatever the class that implements this interface, it must also expose either a public no-arg constructor, or (for implementations that also are Facets) a public constructor that accepts a single FacetHolder. This constructor allows the framework to instantiate the object reflectively.

See Also:

DefaultsProvider, EncoderDecoder, ValueSemanticsProvider

Method Summary

java.lang.String	displayTitleOf(T object) The title of the object.
java.lang.String	parseableTitleOf(T existing) A title for the object that is valid but which may be easier to edit than the title provided by a org.nakedobjects.metamodel.facets.object.ident.TitleFacet.
T	parseTextEntry(T context, java.lang.String entry) Parses a string to an instance of the object.
int	typicalLength() The typical length of objects that can be parsed.

Method Detail

parseTextEntry

T parseTextEntry(T context,
                 java.lang.String entry)

Parses a string to an instance of the object.

Note that here the implementing class is acting as a factory for itself.

Parameters:

context - - the context in which the text is being parsed. For example +3 might mean add 3 to the current number.

typicalLength

int typicalLength()

The typical length of objects that can be parsed.

displayTitleOf

java.lang.String displayTitleOf(T object)

The title of the object.

parseableTitleOf

java.lang.String parseableTitleOf(T existing)

A title for the object that is valid but which may be easier to edit than the title provided by a org.nakedobjects.metamodel.facets.object.ident.TitleFacet.

The idea here is that the viewer can display a parseable title for an existing object when, for example, the user initially clicks in the field. So, a date might be rendered via a TitleFacet as May 2, 2007, but its editable form might be 20070502.