lp.struct
Class LpPredicate

java.lang.Object
  lp.struct.LpAbstractStructureUnit
      lp.struct.LpPredicate

All Implemented Interfaces:

LpStructureUnit

public class LpPredicate
extends LpAbstractStructureUnit

Represents a predicate (symbol) in logic programming. Each predicate has a name and an arity, i.e. a non-negative integer that specifies the number of terms (see LpTerm) that it takes as arguments. LpPredicates are immutable.

Version:

1.0.0

Author:

Martin Slota

See Also:

LpTerm, LpLiteral

Field Summary

private int	arity This predicate's arity.
private String	name This predicate's name.
private static Map<String,LpPredicate>	pool A pool of instances of this immutable class.

Fields inherited from class lp.struct.LpAbstractStructureUnit

TO_STRING_BUFFER

Constructor Summary

protected

LpPredicate(String name, int arity) Creates a new instance with the given name and arity.

Method Summary

void	accept(LpStructureUnitVisitor visitor) Accepts LpStructureUnitVisitor instance, i.e. calls its visitor.visit(this).
boolean	equals(Object obj) Returns true if and only if obj is a LpPredicate instance, its name is equal to this predicate's name as defined by String.equals(Object), its arity is equal to this predicate's arity
int	getArity() Returns this predicate's arity.
static LpPredicate	getInstance(String name, int arity) Returns and instance of LpPredicate with the given name and arity.
static LpPredicate	getInstance(String name, List<LpTerm> arguments) Returns and instance of LpPredicate with the given name and arity implied by the size of the given argument list.
String	getName() Returns this predicate's name, the same that was given to the constructor.
int	hashCode() Overriden in order to maintain the general contract of Object.hashCode().
String	toString() Overrides the behaviour of LpAbstractStructureUnit.toString().

Methods inherited from class lp.struct.LpAbstractStructureUnit

toUnmodifiableList, toUnmodifiableSet

Methods inherited from class java.lang.Object

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

Field Detail

pool

private static final Map<String,LpPredicate> pool

A pool of instances of this immutable class. The getInstance(String, int) method first looks here for the requested instances and if it is forced to create a new one, it is added to this pool.

name

private final String name

This predicate's name.

arity

private final int arity

This predicate's arity.

Constructor Detail

LpPredicate

protected LpPredicate(String name,
                      int arity)

Creates a new instance with the given name and arity. name is required to be a non-empty string and arity must be non-negative.

Parameters:

name - the name of the predicate

arity - the predicate's arity

Throws:

IllegalArgumentException - if name is null or name is an empty string or arity is negative

Method Detail

getInstance

public static LpPredicate getInstance(String name,
                                      int arity)

Returns and instance of LpPredicate with the given name and arity. name is required to be a non-empty string and arity must be non-negative.

Parameters:

name - the name of the requested predicate

arity - the requested predicate's arity

Throws:

IllegalArgumentException - if name is null or name is an empty string or arity is negative

getInstance

public static LpPredicate getInstance(String name,
                                      List<LpTerm> arguments)

Returns and instance of LpPredicate with the given name and arity implied by the size of the given argument list. name is required to be a non-empty string.

Parameters:

name - the name of the requested predicate

arguments - the sample argument list, its size is the predicate's arity (it can also be null, in that case a predicate with arity 0 is returned)

Throws:

IllegalArgumentException - if name is null or name is an empty string

getName

public String getName()

Returns this predicate's name, the same that was given to the constructor.

Returns:

the name of this predicate

getArity

public int getArity()

Returns this predicate's arity. Guaranteed to be non-negative.

Returns:

this predicate's arity

accept

public void accept(LpStructureUnitVisitor visitor)

Accepts LpStructureUnitVisitor instance, i.e. calls its visitor.visit(this).

Parameters:

visitor - the visitor to accept

equals

public boolean equals(Object obj)

Returns true if and only if

1. obj is a LpPredicate instance,
2. its name is equal to this predicate's name as defined by String.equals(Object),
3. its arity is equal to this predicate's arity

Overrides:

equals in class Object

Parameters:

obj - the object to compare with

Returns:

true if this object is equal to obj according to the description above, and false otherwise

See Also:

String.equals(Object)

hashCode

public int hashCode()

Overriden in order to maintain the general contract of Object.hashCode().

Overrides:

hashCode in class Object

Returns:

the hash of this object

See Also:

String.hashCode()

toString

public String toString()

Overrides the behaviour of LpAbstractStructureUnit.toString(). Returns the normal form (i.e. the predicate's name) followed by a "/" and arity.

Overrides:

toString in class LpAbstractStructureUnit