ai.search
Class AbstractSearchStateForIntCostFn

java.lang.Object
  ai.search.AbstractSearchStateForIntCostFn

All Implemented Interfaces:

SearchStateForIntCostFn

public abstract class AbstractSearchStateForIntCostFn
extends java.lang.Object
implements SearchStateForIntCostFn

This class represents a state of the world in a search problem.

Together with an appropriate implementation for actions, an implementation of a SearchStateForIntCostFn defines a search problem, which consists of four components:

• the initial state: the state from which the search will start; an instance of this class
• the successor function: a function that generates the successor states for a given state; must be implemented through successors() in this class
• the goal test function: a function that tests whether a given state is a goal state; must be implemented through isGoalState() in this class
• the action cost function: a function that computes the cost of applying a given action in a given state; implemented in the IntCostAction class

Given a definition of a search problem in terms of these components and implemented by a class for SearchStateForIntCostFns and a class for IntCostActions, a search engine can be used to attempt to solve the search problem.

The extend this class one of the functions successors() or getAllPossibleActions() must be overridden. Only one of the default implementations provided here can be used. If getAllPossibleActions() is overridden the Array returned by this function is used to create a generic Iterator to be returned by successors(). This approach should only be used if there are few actions, most of which are usually applicable. Otherwise the function successors() should be overridden and this can create a more efficient Iterator to enumerate the successors of this state.

Author:

Gerhard Wickler

See Also:

IntCostAction, SearchEngineForIntCostFn

Nested Class Summary

(package private) class

AbstractSearchStateForIntCostFn.GenericSuccessorIterator

Constructor Summary

AbstractSearchStateForIntCostFn()

Method Summary

abstract IntCostAction[]	getAllPossibleActions() This function returns an array of all the actions that are in principle possible in this state.
java.util.Iterator<inf.util.Pair<IntCostAction,SearchStateForIntCostFn>>	successors() This function indirectly generates the successors for this state in the context of the search problem defined by this class.

Methods inherited from class java.lang.Object

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

Methods inherited from interface ai.search.SearchStateForIntCostFn

apply, getActionClass, isApplicable, isGoalState

Constructor Detail

AbstractSearchStateForIntCostFn

public AbstractSearchStateForIntCostFn()

Method Detail

getAllPossibleActions

public abstract IntCostAction[] getAllPossibleActions()

This function returns an array of all the actions that are in principle possible in this state. There is no guarantee that these actions are also applicable. If this function is implemented correctly then the default implementation of successors() will return a correctly working Iterator. This default implementation only throws an UnsupportedOperationException.

Extensions of this class should override either this function or successors().

Returns:

an Array containing all potentially applicable IntCostActions

successors

public java.util.Iterator<inf.util.Pair<IntCostAction,SearchStateForIntCostFn>> successors()

This function indirectly generates the successors for this state in the context of the search problem defined by this class. The returned Iterator will generate a sequence of Pairs consisting of an IntCostAction and a SearchStateForIntCostFn, where the action if applied in this state will result in the paired state.

The default implementation provided here relies on the function getAllPossibleActions() to work correctly. Extensions of this class should override either this function or getAllPossibleActions().

Specified by:

successors in interface SearchStateForIntCostFn

Returns:

an Iterator over the successor states of this state