org.geotools.event
Interface GTDelta

All Known Implementing Classes:

GTDeltaImpl

public interface GTDelta

Indicates which style constructs have been changed.

Acts as a series of breadcrumbs stored up by a StyleEvent to communicate changes.

This delta is constructed a fashion following the outline of the style document, allowing you to skip over entire branches of changes if you are not interested.

Example Use

The following examples will make use of the following allegorical data structure

 Root
  +--Parent
       +-- Child
       +-- List
             [0]--Element
 

These roles are allegorical in nature any may be played in real life by arrays, beans, collections, etc.. (as example StyleLayerDescriptor is a "Root").

Example 0: An Child is changed.

 Event.POST_CHANGE
    +---Delta1 "" -1 NO_CHANGE(Root,null,)
           +---Delta2 "Parent" -1 NO_CHANGE (Parent, null )
                  +---Delta3 "Child" -1 CHANGED (Child, oldChild )
 

Location of change is indicated by delta, including name of "Child". The oldChild is provided incase you need to un-listen or something. Parent is not considered to have changed itself (it is still has the same structure).

Example 1: An Element is changed:

 Event.POST_CHANGE
    +---Delta1 "" -1 NO_CHANGE(Root,null,)
           +---Delta2 "Parent" -1 NO_CHANGE (Parent, null )
                  +---Delta3 "List" 0 CHANGED (Element, null )
 

Location of change is indicated by delta, including position in list. Children in lists are children too, delta intentionally similar to the last.

Example 2: A new Element2 is added:

 Event.POST_CHANGE
    +---Delta1 "" -1 NO_CHANGE(Root,null,)
           +---Delta2 "Parent" -1 CHANGED (Parent, null )
                  +---Delta3 "List" 1 ADDED (Element2, null )
 

Adding Element2 results in a change to Parent (it is structured diffrently). Position of the change in the "List" is indicated.

Example 3: Swap Element and Element2

 Event.POST_CHANGE
    +---Delta1 "" -1 NO_CHANGE(Root,null,)
           +---Delta2 "Parent" -1 CHANGED (Parent, null )
                  +---Delta3 "List" 1 NO_CHANGE (Element, null )
                  +---Delta4 "List" 0 NO_CHANGE (Element2, null )
 

Moving things around does not change them, but it is a change to the Parent.

Example 5: Remove Element2

 Event.POST_CHANGE
    +---Delta1 "" -1 NO_CHANGE(Root,null,)
           +---Delta2 "Parent" -1 CHANGED (Parent, null )
                  +---Delta3 "List" -1 REMOVED ( null, Element2 )
                  +---Delta4 "List" 0 NO_CHANGE (Element, null )
 

Removing also is a considered a change to Parent, note this is a POST_CHANGE event so Element2 is an oldValue. The NO_CHANGE for Element is similar to Example4, it still indicates a change of position.

Example 6: Go Fish

 Event.POST_CHANGE
    +---Delta1 "" -1 CHANGED(Root,null,)
 

Something changed somewhere, similar to "touch".

Example 7: Shutting Down

 Event.PRE_CLOSE
    +---Delta1 "" -1 NO_CHANGE(Root,null,)
 

That was easy then...

You should be aware that the event system may "collapse" events that duplicate information, especially when considering batch changes resulting from the application of a visitor or transformation.

Author:

Jody Garnett, Refractions Research

Nested Class Summary

static class

GTDelta.Kind Kind of Delta, used to indicate change.

Field Summary

static java.util.List	NO_CHILDREN List indicating no children are present
static int	NO_INDEX Index position is not to be considered relevent

Method Summary

void	accept(GTDeltaVisitor visitor) Accepts the given visitor.
java.util.List	getChildren() Finds and returns deltas for specificly changed constructs.
GTDelta.Kind	getKind() Returns the kind of this delta.
java.lang.String	getName() Name of property being affected.
java.lang.Object	getOldValue() Construct being replaced with a changed, getValue is the replacing value.
int	getPosition() Position in a "list" where the change occured, or NO_INDEX.
java.lang.Object	getValue() Affected construct, getKind & getChildern indicate specific details of the change.

Field Detail

NO_CHILDREN

public static final java.util.List NO_CHILDREN

List indicating no children are present

NO_INDEX

public static final int NO_INDEX

Index position is not to be considered relevent

See Also:

Constant Field Values

Method Detail

getKind

public GTDelta.Kind getKind()

Returns the kind of this delta.

Normally, one of ADDED, REMOVED or CHANGED.

Returns:

the kind of this resource delta

See Also:

Kind.ADDED, Kind.REMOVED, Kind.CHANGED

getValue

public java.lang.Object getValue()

Affected construct, getKind & getChildern indicate specific details of the change.

Returns:

Affected construct

getOldValue

public java.lang.Object getOldValue()

Construct being replaced with a changed, getValue is the replacing value.

Returns:

Affected construct

getPosition

public int getPosition()

Position in a "list" where the change occured, or NO_INDEX.

Returns:

Position in "list" or NO_INDEX.

getName

public java.lang.String getName()

Name of property being affected.

• propertyName: "bean" property name when intergrating third party Java Beans into a more complex tree structure.
• List and Arrays: the name of the list, and may be combined with getPosition to indicate location, NO_INDEX would indicate the entire "list" has been modified.

Returns:

name of affected Child, or null for root

getChildren

public java.util.List getChildren()

Finds and returns deltas for specificly changed constructs.

This code may be considered more accessable then the use of GTDeltaVisitor.

Returns:

List of StyleDelta

accept

public void accept(GTDeltaVisitor visitor)

Accepts the given visitor.

Parameters:

visitor -