Adds the given Observer to this Subject's list of Observers, so that the Observer
will be notified of changes in this Subject. An Observer may call Subject.addObserver
during its observe method.
the Observer to add
Notifies all Observers that this Subject has changed by calling observe on each Observer.
An Observer may call addObserver or removeObserver during its observe
method.
a SubjectEvent with information relating to the change
Notifies all Observers that the Parameter with the given name has changed by calling observe on each Observer.
the language-independent or English name of the Parameter that has changed
if there is no Parameter with the given name
Returns the ParameterBoolean with the given name.
the language-independent or English name of the ParameterBoolean
the ParameterBoolean with the given name
if there is no ParameterBoolean with the given name
Returns the ParameterNumber with the given name.
the language-independent or English name of the ParameterNumber
the ParameterNumber with the given name
if there is no ParameterNumber with the given name
Returns the ParameterString with the given name.
the language-independent or English name of the ParameterString
the ParameterString with the given name
if there is no ParameterString with the given name
Removes the Observer from this Subject's list of Observers. An Observer may
call removeObserver during its observe method.
the Observer to detach from list of Observers
Returns a minimal string representation of this object, usually giving just identity information like the class name and name of the object.
For an object whose main purpose is to represent another Printable object, it is
recommended to include the result of calling toStringShort on that other object.
For example, calling toStringShort() on a DisplayShape might return something like
this:
DisplayShape{polygon:Polygon{'chain3'}}
a minimal string representation of this object.
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A Subject notifies its Observer when something changes in the Subject. This can be a change in the value of a Parameter, or the occurrence of a GenericEvent. The Subject maintains a list of its Observers. An Observer is connected to the Subject via the addObserver method, which is typically called by the Observer's constructor or the entity that creates the Observer.
See Subject, Observer, Parameter for an overview. The Subject and Observer interfaces are an implementation of the Observer design pattern.
When a change occurs in the Subject, the broadcast method should be called to inform all Observers of the change. For a Parameter, the "setter" method of the Subject should call broadcastParameter at the end of the setter method.
Language-Independent Names
To enable scripting, we need Parameters and SubjectEvents to have language independent names. Therefore
Parameter.getName()andSubjectEvent.getName()return a language independent name which is derived from the English localized name by converting the English name to uppercase and replacing spaces and dashes by underscore.You can use the function Util.toName to convert an English name to the language-independent name. Or use
SubjectEvent.nameEquals()which handles the conversion to language independent name.See Internationalization for more about localized and language-independent strings.
Example Scenario
Here is an example usage of the Subject and Observer interfaces, along with Parameters and user interface controls.
The diagram shows a ContactSim as the Subject. It has a list of Parameters, including a Parameter representing the distance tolerance which determines when objects are in contact. The Subject also has a list of Observers, including a NumericControl which is connected to the distance tolerance ParameterNumber. In its constructor, the NumericControl adds itself to the list of Observers by calling addObserver on the Subject of the ParameterNumber.
Whenever the distance tolerance is changed, the Subject should notify each Observer by calling broadcast. The Observer can then get the current value by calling
ParameterNumber.getValue.This design is very decoupled. The Subject knows nothing about the NumericControl except that it is an Observer. The Parameter is unaware of the NumericControl. The NumericControl only knows about the ParameterNumber and that it has a Subject which will provide notification of changes.