Package org.projog.core.predicate

Class PredicateKey

java.lang.Object

org.projog.core.predicate.PredicateKey

All Implemented Interfaces:

java.lang.Comparable<PredicateKey>

public final class PredicateKey
extends java.lang.Object
implements java.lang.Comparable<PredicateKey>

Represents the structure of a Term.

Defines Terms by their name (functor) and number of arguments (arity). This "metadata" or "descriptor information" allows rules whose heads (consequences) share the same structure to be grouped together.

As Atom and Structure are the only subclasses of Term that can be the head (consequent) of a rule they are the only subclasses of Term that PredicateKey is intended to describe.

PredicateKeys are constant; their values cannot be changed after they are created.

Field Summary

Fields

Modifier and Type	Field	Description
private java.lang.String	name
private int	numArgs
private static java.lang.String	PREDICATE_KEY_FUNCTOR

Constructor Summary

Constructors

Constructor	Description
PredicateKey(java.lang.String name, int numArgs)

Method Summary

Modifier and Type	Method	Description
int	compareTo(PredicateKey o)	Ordered on name or, if names identical, number of arguments.
static PredicateKey	createForTerm(Term t)	Returns a PredicateKey for the specified term.
static PredicateKey	createFromNameAndArity(Term t)
boolean	equals(java.lang.Object o)
private static java.lang.String	getInvalidTypeExceptionMessage(Term t)
java.lang.String	getName()
int	getNumArgs()
int	hashCode()
java.lang.String	toString()
Term	toTerm()

Methods inherited from class java.lang.Object

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

Field Detail

PREDICATE_KEY_FUNCTOR

private static final java.lang.String PREDICATE_KEY_FUNCTOR

See Also:

Constant Field Values

name

private final java.lang.String name

numArgs

private final int numArgs

Constructor Detail

PredicateKey

public PredicateKey(java.lang.String name,
                    int numArgs)

Method Detail

createForTerm

public static PredicateKey createForTerm(Term t)

Returns a PredicateKey for the specified term.

Parameters:

t - a term the returned PredicateKey should represent (needs to have a Term.getType() value of TermType.ATOM or TermType.STRUCTURE)

Returns:

a PredicateKey for the specified term.

Throws:

ProjogException - if t is not of type TermType.ATOM or TermType.STRUCTURE

createFromNameAndArity

public static PredicateKey createFromNameAndArity(Term t)

Parameters:

t - must be a structure named / where the first argument is the name of the predicate to represent and the second (and final) argument is the arity.

getInvalidTypeExceptionMessage

private static java.lang.String getInvalidTypeExceptionMessage(Term t)

getName

public java.lang.String getName()

getNumArgs

public int getNumArgs()

toTerm

public Term toTerm()

equals

public boolean equals(java.lang.Object o)

Overrides:

equals in class java.lang.Object

Parameters:

o - the reference object with which to compare.

Returns:

true if o is an instanceof PredicateKey and has the same name and number of arguments as this instance

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

Returns:

name+"/"+numArgs

compareTo

public int compareTo(PredicateKey o)

Ordered on name or, if names identical, number of arguments.

Specified by:

compareTo in interface java.lang.Comparable<PredicateKey>