aima.core.search.framework

Class NodeExpander

java.lang.Object

aima.core.search.framework.NodeExpander

public class NodeExpander
extends java.lang.Object

Instances of this class are responsible for node creation and expansion. They compute path costs, support progress tracing, and count the number of expand(Node, Problem) calls.

Author:

Ruediger Lunde

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	NodeExpander.NodeListener Interface for progress Tracers

Field Summary

Fields

Modifier and Type	Field and Description
protected int	counter Counts the number of expand(Node, Problem) calls.
protected boolean	useParentLinks

Constructor Summary

Constructors

Constructor and Description
NodeExpander()

Method Summary

Modifier and Type	Method and Description
void	addNodeListener(NodeExpander.NodeListener listener) Adds a listener to the list of node listeners.
Node	createNode(java.lang.Object state, Node parent, Action action, double stepCost) Computes the path cost for getting from the root node state via the parent node state to the specified state, creates a new node for the specified state, adds it as child of the provided parent (if useParentLinks is true), and returns it.
Node	createRootNode(java.lang.Object state) Factory method, which creates a root node for the specified state.
java.util.List<Node>	expand(Node node, Problem problem) Returns the children obtained from expanding the specified node in the specified problem.
int	getNumOfExpandCalls() Returns the number of expand(Node, Problem) calls since the last counter reset.
protected void	notifyNodeListeners(Node node)
void	resetCounter() Resets the counter for expand(Node, Problem) calls.
NodeExpander	useParentLinks(boolean state) Modifies useParentLinks and returns this node expander.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

useParentLinks

protected boolean useParentLinks

counter

protected int counter

Counts the number of expand(Node, Problem) calls.

Constructor Detail

NodeExpander

public NodeExpander()

Method Detail

useParentLinks

public NodeExpander useParentLinks(boolean state)

Modifies useParentLinks and returns this node expander. When using local search to search for states, parent links are not needed and lead to unnecessary memory consumption.

Returns:

createRootNode

public Node createRootNode(java.lang.Object state)

Factory method, which creates a root node for the specified state.

createNode

public Node createNode(java.lang.Object state,
                       Node parent,
                       Action action,
                       double stepCost)

Computes the path cost for getting from the root node state via the parent node state to the specified state, creates a new node for the specified state, adds it as child of the provided parent (if useParentLinks is true), and returns it.

expand

public java.util.List<Node> expand(Node node,
                                   Problem problem)

Returns the children obtained from expanding the specified node in the specified problem.

Parameters:

node - the node to expand

problem - the problem the specified node is within.

Returns:

the children obtained from expanding the specified node in the specified problem.

addNodeListener

public void addNodeListener(NodeExpander.NodeListener listener)

Adds a listener to the list of node listeners. It is informed whenever a node is expanded during search.

notifyNodeListeners

protected void notifyNodeListeners(Node node)

resetCounter

public void resetCounter()

Resets the counter for expand(Node, Problem) calls.

getNumOfExpandCalls

public int getNumOfExpandCalls()

Returns the number of expand(Node, Problem) calls since the last counter reset.