org.projog.core.term

Class Atom

java.lang.Object

org.projog.core.term.Atom

All Implemented Interfaces:

Term

public final class Atom
extends Object
implements Term

Represents a specific object or relationship.

Atoms are constant; their values cannot be changed after they are created. Atoms have no arguments.

Constructor Summary

Constructors

Constructor and Description
Atom(String value)

Method Summary

Modifier and Type	Method and Description
void	backtrack() Reverts this term back to its original state prior to any unifications.
Atom	copy(Map<Variable,Variable> sharedVariables) Returns a copy of this term.
boolean	equals(Object o)
Term[]	getArgs() Returns an array of this terms's arguments.
Term	getArgument(int index) Returns the term at the specified position in this term's arguments.
String	getName() Returns the value this Atom represents.
int	getNumberOfArguments() Returns the number of arguments in this term.
Atom	getTerm() Returns the current instantiated state of this term.
TermType	getType() Returns TermType.ATOM.
int	hashCode()
boolean	isImmutable() Returns true is this term is immutable.
String	toString()
boolean	unify(Term t) Attempts to unify this term to the specified term.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface org.projog.core.term.Term

getBound

Constructor Detail

Atom

public Atom(String value)

Parameters:

value - the value this Atom represents

Method Detail

getName

public String getName()

Returns the value this Atom represents.

Specified by:

getName in interface Term

Returns:

the value this Atom represents

getArgs

public Term[] getArgs()

Description copied from interface: Term

Returns an array of this terms's arguments.

Note: for performance reasons the array returned is the same array used internally be the term instance so be careful not to alter the array returned as changes will be reflected in the original term.

Specified by:

getArgs in interface Term

Returns:

array of this terms's arguments

See Also:

Term.getArgument(int)

getNumberOfArguments

public int getNumberOfArguments()

Description copied from interface: Term

Returns the number of arguments in this term.

Specified by:

getNumberOfArguments in interface Term

Returns:

number of arguments in this term

getArgument

public Term getArgument(int index)

Description copied from interface: Term

Returns the term at the specified position in this term's arguments.

Specified by:

getArgument in interface Term

Parameters:

index - index of the argument to return

Returns:

the term at the specified position in this term's arguments

Throws:

ArrayIndexOutOfBoundsException - as this implementation of Term has no arguments

getType

public TermType getType()

Returns TermType.ATOM.

Specified by:

getType in interface Term

Returns:

TermType.ATOM

isImmutable

public boolean isImmutable()

Description copied from interface: Term

Returns true is this term is immutable.

A term is considered immutable if its value will never change as a result of executing its Term.unify(Term) or Term.backtrack() methods. A term will not be considered immutable if it is a Variable or any of its arguments are not immutable.

Specified by:

isImmutable in interface Term

Returns:

true is this term is immutable

copy

public Atom copy(Map<Variable,Variable> sharedVariables)

Description copied from interface: Term

Returns a copy of this term.

The returned copy will share any immutable terms contained in this term. The returned copy will contain new instances for any Variables contained in this term. The sharedVariables parameter keeps track of which Variables have already been copied.

Specified by:

copy in interface Term

Parameters:

sharedVariables - keeps track of which Variables have already been copied (key = original version, value = version used in copy)

Returns:

a copy of this term

getTerm

public Atom getTerm()

Description copied from interface: Term

Returns the current instantiated state of this term.

Returns a representation of this term with all instantiated Variables replaced with the terms they are instantiated with.

Specified by:

getTerm in interface Term

Returns:

a representation of this term with all instantiated Variables replaced with the terms they are instantiated with.

unify

public boolean unify(Term t)

Description copied from interface: Term

Attempts to unify this term to the specified term.

The rules for deciding if two terms are unifiable are as follows:

• An uninstantiated Variable will unify with any term. As a result the Variable will become instantiated to the other term. The instantiaton will be undone when Term.backtrack() is next called on the Variable
• Non-variable terms will unify with other terms that are of the same TermType and have the same value. The exact meaning of "having the same value" will vary between term types but will include that the two terms being unified have the same number of arguments and that all of their corresponding arguments unify.

Note: can leave things in "half-state" on failure as neither List or Predicate backtrack earlier args.

Specified by:

unify in interface Term

Parameters:

t - the term to unify this term against

Returns:

true if the attempt to unify this term to the given term was successful

See Also:

Term.backtrack()

backtrack

public void backtrack()

Description copied from interface: Term

Reverts this term back to its original state prior to any unifications.

Makes all Variables that this term consists of uninstantiated.

Specified by:

backtrack in interface Term

See Also:

Term.unify(Term)

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object

Returns:

getName()