org.geotools.graph.traverse.standard

## Class AStarIterator

• All Implemented Interfaces:
GraphIterator

```public class AStarIterator
extends SourceGraphIterator```
A path iterator that uses a function (usually denoted f(x)) to determine the order in which the algorithm visits nodes, f(x) is a sum of two functions:
• The path-cost function (usually denoted g(x), which may or may not be a heuristic)
• An admissible "heuristic estimate" (usually denoted h(x)).
The iterator proceeds as follows (pseudo-code):
``` ```
// COST(n,n') : the real cost to go from n to n'
OPEN = [Source]
CLOSE = []

while ( |OPEN| > 0 )
n = a node in OPEN with less f
remove n from OPEN
add n to CLOSE
if ( n == target ) {
return  // path find

// if n != target
for each node n' that relates to n do
if n' in OPEN
if (g(n) + COST(n,n')) < g(n')
g(n') = g(n) + COST(n,n')
parent(n') = n
else
g(n') = g(n) + COST(n,n')
parent(n') = n
add n' to OPEN
// end while
```
```
For more details see http://en.wikipedia.org/wiki/A_star
Author:
Germán E. Trouillet, Francisco G. Malbrán. Universidad Nacional de Córdoba (UNC)
• ### Nested Class Summary

Nested Classes
Modifier and Type Class and Description
`static class ` `AStarIterator.AStarFunctions`
Defines the functions needed by A Star.
`static class ` `AStarIterator.AStarNode`
Internal data structure used to track node costs, and parent nodes.
• ### Constructor Summary

Constructors
Constructor and Description
```AStarIterator(Node source, AStarIterator.AStarFunctions afuncs)```
• ### Method Summary

All Methods
Modifier and Type Method and Description
`void` ```cont(Graphable current, GraphTraversal traversal)```
Makes a step of the A* algorithm.
`Node` `getParent(Node n)`
`protected Iterator<?>` `getRelated(Graphable current)`
`void` ```init(Graph graph, GraphTraversal traversal)```
Does Nothing.
`void` ```killBranch(Graphable current, GraphTraversal traversal)```
Kills the branch of the traversal
`Graphable` `next(GraphTraversal traversal)`
Returns the next node in the priority queue. if the queue is empty then there is no path from the source to the destiny in this graph.
• ### Methods inherited from class SourceGraphIterator

`getSource, setSource`
• ### Methods inherited from class AbstractGraphIterator

`getGraph, getTraversal, getWalker, setTraversal`
• ### Methods inherited from class Object

`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`
• ### Constructor Detail

• #### AStarIterator

```public AStarIterator(Node source,
AStarIterator.AStarFunctions afuncs)```
• ### Method Detail

• #### init

```public void init(Graph graph,
GraphTraversal traversal)```
Does Nothing. All the work was already done by the constructor.
Parameters:
`graph` - The graph being whose components are being iterated over.
• #### next

`public Graphable next(GraphTraversal traversal)`
Returns the next node in the priority queue. if the queue is empty then there is no path from the source to the destiny in this graph.
Returns:
The next component in the iteration, or null if iteration is complete.
See Also:
`org.geotools.graph.traverse.GraphIterator#next()`
• #### cont

```public void cont(Graphable current,
GraphTraversal traversal)```
Makes a step of the A* algorithm. Takes the current node, looks for its neighbours. The ones which are closed are discarted. The ones "in" the opened queue are checked to see if its necessary to update them. The rest of the nodes are initialized as AStarNodes and inserted in the opened queue.
Parameters:
`current` - The current component of the traversal.
See Also:
`org.geotools.graph.traverse.GraphIterator#cont(Graphable)`
• #### killBranch

```public void killBranch(Graphable current,
GraphTraversal traversal)```
Kills the branch of the traversal
Parameters:
`current` - The current component of the traversal.
See Also:
`org.geotools.graph.traverse.GraphIterator#killBranch(Graphable)`
• #### getParent

`public Node getParent(Node n)`
• #### getRelated

`protected Iterator<?> getRelated(Graphable current)`

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