lp.struct
Class LpConstant

java.lang.Object
  lp.struct.LpAbstractStructureUnit
      lp.struct.LpConstant

All Implemented Interfaces:

LpStructureUnit, LpTerm

public class LpConstant
extends LpAbstractStructureUnit
implements LpTerm

Represents a constant in logic programming. Constants are, together with function symbols and variables (see LpFunction and LpVariable) building units of terms (see LpTerm. Each constant has a unique non-empty name. LpConstants are immutable.

Version:

1.0.0

Author:

Martin Slota

See Also:

LpTerm

Field Summary

private String	name This constant's name.
private static Map<String,LpConstant>	pool A pool of instances of this immutable class.

Fields inherited from class lp.struct.LpAbstractStructureUnit

TO_STRING_BUFFER

Constructor Summary

protected

LpConstant(String name) Creates a new instance of LpConstant with the given name.

Method Summary

void	accept(LpStructureUnitVisitor visitor) Accepts LpStructureUnitVisitor instance, i.e. calls visitor.visit(this).
boolean	equals(Object obj) Returns true if and only if obj is a LpConstant instance, its name is equal to this constant's name as defined by String.equals(Object),
static LpConstant	getInstance(String name) Returns an instance of LpConstant with the given name.
String	getName() Returns this constant's name, the same that was given to the constructor.
int	hashCode() Overriden in order to maintain the general contract of Object.hashCode().

Methods inherited from class lp.struct.LpAbstractStructureUnit

toString, 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,LpConstant> pool

A pool of instances of this immutable class. The getInstance(String) 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 constant's name.

Constructor Detail

LpConstant

protected LpConstant(String name)

Creates a new instance of LpConstant with the given name.

Parameters:

name - the new constant's name

Throws:

IllegalArgumentException - if name is null or an empty string

Method Detail

getInstance

public static LpConstant getInstance(String name)

Returns an instance of LpConstant with the given name.

Parameters:

name - the requested constant's name

Throws:

IllegalArgumentException - if name is null or an empty string

getName

public String getName()

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

Returns:

the name of this contant

accept

public void accept(LpStructureUnitVisitor visitor)

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

Specified by:

accept in interface LpStructureUnit

Parameters:

visitor - the visitor to accept

equals

public boolean equals(Object obj)

Returns true if and only if

1. obj is a LpConstant instance,
2. its name is equal to this constant's name as defined by String.equals(Object),

Specified by:

equals in interface LpTerm

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), LpTerm.equals(Object)

hashCode

public int hashCode()

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

Specified by:

hashCode in interface LpTerm

Overrides:

hashCode in class Object

Returns:

the hash of this object

See Also:

String.hashCode(), LpTerm.equals(Object)