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Interface uhr.core.role.Delegator

public interface Delegator
This interface allows a class to have delegates. A delegate performs part of a class's responsibilities. The strategic goal is to allow more responsibility in a single class without causing more complexity. This is accomplished by the delegate being separately encapsulated. Furthermore, the class may provide a delegate or it may be provided for it.

This provides the Exposed Delegator Pattern for parts. This pattern allows clients to get and use a part's Delegate for certain responsiblities. This greately reduces the size and complexitiy of some parts, allows loose coupling between the Delegate and it's host, etc. Note how the host can provide its own Delegate, or it can be set by a Mediator. This pattern allows a slew of radical framework improvements.

One example is a Cell has a "StateCommandable" Delegate which is the CellLifecycle. The Cell never even knows it has this Delegate.

A great advantage is when looping through parts in a collection to check for a certain interface, say InterfaceA. As Steve pointed out, by doing the Delegate check first we allow the Delegate to shadow the part's InterfaceA. The algorithm is:

1. If the part implements Delegator and has the InterfaceA Delegate, use it.

2. If the part implements the InterfaceA, use that.

3. Otherwise assume the part doesn't support InterfaceA.

The greatest good is achieved when delegates are provided for a class and the class never even knows they're there. These "hidden" delegates usually have a reference to the delegator. The delegator should not use them for anything, and pretend they're not even there.

Hidden delegates should be kept in something like a Hashtable. Since we are planning for mostly this, we return an Enumeration instead of a String[] for the delegate names. This makes the implementation easier.

Method Index

o getDelegate(String)
Returns the named delegate or null if none.
o getDelegateNames()
Returns an enumeration of all the delegate names in no particular order.
o setDelegate(String, Object)
Sets the named delegate.

Methods

o getDelegate 
 public abstract Object getDelegate(String delegateName)
Returns the named delegate or null if none. This may safely be used instead of a method like: 
     public boolean hasDelegate();
which would be redundant and a perfromance hit since if true you must get the delegate anyhow.

Parameters:
delegateName - the name of the desired delegate.
Returns:
the named delegate or null if none.
o setDelegate 
 public abstract void setDelegate(String delegateName,
                                  Object delegate)
Sets the named delegate.

Parameters:
delegateName - the name of the delegate, which must be unique within the Delegator.
delegate - the delegate instance.
o getDelegateNames 
 public abstract Enumeration getDelegateNames()
Returns an enumeration of all the delegate names in no particular order.

Returns:
an enumeration of the delegate names. 
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