| org.geotools.graph.traverse.GraphIterator
All known Subclasses: org.geotools.graph.traverse.basic.AbstractGraphIterator,
| GraphIterator | | public interface GraphIterator (Code) | | Defines an algorithm in which to traverse the components of a graph.
A graph iterator operates by repeatedly returing graph components to the
caller. The order in which to return the components is specific to the
iterator. However, most iterators follow the following conventions:
- Components are visited only once
- The next component to be returned is determined by the components that
have been previously visited
The following is an example of a GraphIterator. It returns nodes of a graph
in a standard Depth First Search order, starting from a specified node.
The nodes have been numbered to correspond to the iteration pattern.
indicates source of traversal
In order to analyze the traversal, the following terms are defined:
The Next Set of a traversal is the set of components that will be
visited in a later stage of the traversal.
The Branch Set of an component e is defined as the set of
components that can be visited in a later stage of the traversal as a direct
result of visiting e.
In most traversals, the two sets are related. The Next Set is built by
analyzing the Branch Set of the component being visited in the current stage
of the traversal. Revisiting the above example, a Depth First Search
Traversal operates as follows:
- Each node is visited only once.
- The Next Set is organized as a Last In First Out Queue (Stack).
- At each stage, every node in the Branch Set that has not yet been visited
is added to the Next Set.
As well it is assumed that nodes related to a node are sorted in
alphabetic order.
The following table summarizes the stages of the traversal:
| Stage |
Visited Node |
Branch Set |
Next Set |
Comment |
| 0 |
|
|
{A} |
Initial stage, iteration starts explicitly from A |
| 1 | A | {B,F} | {F,B} |
Related nodes added to Next Set in LIFO order. |
| 2 | F | {A,B} | {B,B} |
A already visited so not added to Next Set
B not yet visited so added to queue. |
| 3 | B | {A,C,D,E,F} | {B,E,D,C} |
A,F already visited so not added to Next Set |
| 4 | B | | {E,D,C} |
B already visited so ignore and move to next stage |
| 5 | E | {B} | {D,C} |
|
| 6 | D | {B,C} | {C,C} |
|
| 7 | C | {B,D} | {C} |
|
| 8 | C | | { } |
C already visited so ignore and move to next stage |
| 9 | | | { } |
Next set empty, iteration complete. |
At any stage of a travesal a branch may be killed.When a branch is
killed at a stage of an iteration, no elements in the current Branch Set
are added to the Next Set. This is illustrated by revisiting the
Depth First Search Iteration, but this time killing the branch at node B.
The following table summarizes the stages of the traversal:
| Stage |
Visited Node |
Branch Set |
Next Set |
Comment |
| 0 |
|
|
{A} |
Initial stage, iteration starts explicitly from A |
| 1 | A | {B,F} | {F,B} |
Related nodes added to Next Set in LIFO order. |
| 2 | F | {A,B} | {B,B} |
A already visited so not added to Next Set
B not yet visited so added to queue. |
| 3 | B | {A,C,D,E,F} | {B} |
Branch Killed. No nodes added to Next Set |
| 4 | B | | { } |
B already visited so ignore and move to next stage |
| 9 | | | { } |
Next set empty, iteration complete. |
In this example, killing the branch at node B results in nodes C, D, and E
never being visited.
See Also: GraphWalker
See Also: GraphTraversal
author:
Justin Deoliveira, Refractions Research Inc, jdeolive@refractions.net |
| cont | | public void cont(Graphable current, GraphTraversal traversal)(Code) | | Signals to the iterator that iteration should continue from the current
component in the traversal.
Parameters:
current - The current component of the traversal. |
| getTraversal | | public GraphTraversal getTraversal()(Code) | | Returns the traversal for the iterator.
The traversal requesting components from the iterator. |
| init | | public void init(Graph graph, GraphTraversal traversal)(Code) | | Signals to the itereator that iteration is about to begin. This often
results in the creation/initialization of any internal data structures
used by the iterator.
Parameters:
graph - The graph being whose components are being iterated over. |
| killBranch | | public void killBranch(Graphable current, GraphTraversal traversal)(Code) | | Signals the iterator to kill the branch at the current component.
Parameters:
current - The current component of the traversal. |
| next | | public Graphable next(GraphTraversal traversal)(Code) | | Returns the next graph component in the iteration. To signal to the caller
that the iteration is complete, null should be returned.
The next component in the iteration, or null if iteration is complete. |
| setTraversal | | public void setTraversal(GraphTraversal traversal)(Code) | | Sets the traversal for the iterator.
Parameters:
traversal - The traversal requesting components from the iterator. |
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