net.java.html.json

Annotation Type ComputedProperty

@Retention(value=SOURCE)
 @Target(value=METHOD)
public @interface ComputedProperty

Can be used in classes annotated with Model annotation to define a derived property. Value of derived property is based on values of Property as enumerated by Model.properties().

The name of the derived property is the name of the method. The arguments of the method must match names and types of some of the properties from Model.properties() list. As soon as one of these properties changes, the method is called to recompute its new value. This applies to inner changes in derived properties as well - e.g. if the dependant property is another type generated by @Model annotation - changes in its own properties trigger recomputation of this derived property as well (since version 0.9).

Method's return type defines the type of the derived property. It may be any primitive type, String, enum type or a type generated by @Model annotation. One may also return an array by returning a list of such (boxed) type (for example List<String> or List<Integer>).

An example testing whether a number is a prime using a ComputedProperty is available on-line.

Author:

Jaroslav Tulach

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
String	write Name of a method to handle changes to the computed property.

Element Detail

write

public abstract String write

Name of a method to handle changes to the computed property. By default the computed properties are read-only, however one can make them mutable by defining a static method that takes two parameters:

1. the model class
2. the value - either exactly the return the method annotated by this property or a superclass (like Object)

Sample code snippet using the write feature of ComputedProperty could look like this (assuming the model class named DataModel has int property value):

 @ComputedProperty(write="setPowerValue")
 static int powerValue(int value) {
   return value * value;
 }
 static void setPowerValue(DataModel m, int value) {
   m.setValue((int)Math.sqrt(value));
 }
 

Returns:

the name of a method to handle changes to the computed property

Since:

1.2

Default:

""