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java.lang.Objectjpl.Query
public class Query
A Query instance is created by an application in order to query the Prolog database (or to invoke a built-in predicate). It is initialised with a Compound (or Atom) denoting the goal which is to be called, and also contains assorted private state relating to solutions. In some future version, it may contain details of the module in which the goal is to be called.
A Query is either open or closed: when closed, it has no connection to the Prolog system; when open, it is linked to an active goal within a Prolog engine.
The Query class implements the Enumeration interface, through which one can obtain successive solutions. The Enumeration hasMoreElements() method returns true if the call or redo succeeded (otherwise false), and if the call or redo did succeed, the nextElement() method returns a Hashtable representing variable bindings; the elements in the Hashtable are Terms, indexed by the (String) names of the Variables with which they are associated. For example, if p(a) and p(b) are facts in the Prolog database, then the following is equivalent to printing all the solutions to the Prolog query p(X):
Variable X = new Variable("X"); Term arg[] = { X }; Query q = new Query("p", arg); while (q.hasMoreElements()){ Term bound_to_x = ((Hashtable) q.nextElement()).get("X"); System.out.println(bound_to_x); }Make sure to close the Query (using the close() method) if you do not need any further solutions which it may have. It is safe (although redundant) to close a Query whose solutions are already exhausted, or which is already closed. To obtain just one solution from a Query, use the oneSolution() method. To obtain all solutions, use the allSolutions() method. To obtain at most N solutions, use the nSolutions() method. To determine merely whether the Query is provable, use the hasSolution() method (i.e. has at least one solution).
Copyright (C) 1998 Fred Dushin
This library is free software; you can redistribute it and/or modify it under the terms of the GNU Library Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library Public License for more details.
Constructor Summary | |
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Query(java.lang.String text)
This constructor builds a Query from the given Prolog source text. |
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Query(java.lang.String text,
Term arg)
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Query(java.lang.String text,
Term[] args)
If text denotes an atom, this constructor is shorthand for new Query(new Compound(name,args)), but if text denotes a term containing N query (?) symbols and there are N args, each query is replaced by its corresponding arg to provide the new Query's goal. |
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Query(Term t)
This constructor creates a Query whose goal is the specified Term. |
Method Summary | |
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int |
abort()
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java.util.Hashtable[] |
allSolutions()
calls the Query's goal to exhaustion and returns an array of zero or more Hashtables of zero or more variablename-to-term bindings (each Hashtable represents a solution, in the order in which they were found). |
static java.util.Hashtable[] |
allSolutions(java.lang.String text)
This static method creates a Query from the given Prolog source text fragment, calls it to exhaustion, and returns an array of zero or more Hashtables of zero or more variablename-to-term bindings (each Hashtable represents a solution, in the order in which they were found). |
static java.util.Hashtable[] |
allSolutions(java.lang.String text,
Term[] params)
If text denotes (in traditional Prolog source syntax) a term containing N questionmark (?) symbols and there are N accompanying Term params, this static method replaces each questionmark symbol by its respective param, calls the resulting goal to exhaustion, and returns an array of zero or more Hashtables of zero or more variablename-to-term bindings (each Hashtable represents a solution, in the order in which they were found). |
static java.util.Hashtable[] |
allSolutions(Term goal)
This static method creates a Query whose goal is the given Term, calls it to exhaustion, and returns an array of zero or more Hashtables of zero or more variablename-to-term bindings (each Hashtable represents a solution, in the order in which they were found). |
Term[] |
args()
Deprecated. Use .goal().args() instead. |
void |
close()
This method can be used to close an open query before its solutions are exhausted. |
java.lang.String |
debugString()
Deprecated. |
java.util.Hashtable |
getSolution()
This method returns a java.util.Hashtable, which represents a set of bindings from the names of query variables to terms within the solution. |
java.util.Hashtable |
getSubstWithNameVars()
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Compound |
goal()
Returns the Compound (hence perhaps an Atom) which is the goal of this Query |
boolean |
hasMoreElements()
This method implements part of the java.util.Enumeration interface. |
boolean |
hasMoreSolutions()
This method returns true if JPL was able to initiate a "call" of this Query within a Prolog engine. |
boolean |
hasSolution()
This method will attempt to call this Query's goal within an available Prolog engine. |
static boolean |
hasSolution(java.lang.String text)
This static method creates a Query from the given Prolog source text and calls it at most once, returning true if a solution was found, else false. |
static boolean |
hasSolution(java.lang.String text,
Term[] params)
If text denotes (in traditional Prolog source syntax) a term containing N questionmark (?) symbols and there are N params, each questionmark symbol is replaced by its corresponding arg to provide the new Query's goal: the resulting Query is called as described above. |
static boolean |
hasSolution(Term goal)
This static method creates a Query (whose goal is the specified Term) and calls it at most once, returning true if a solution was found, else false. |
boolean |
isOpen()
isOpen() returns true iff the query is open. |
java.lang.String |
name()
Deprecated. Use .goal().name() instead. |
java.lang.Object |
nextElement()
This method implements part of the java.util.Enumeration interface. |
java.util.Hashtable |
nextSolution()
This method returns a java.util.Hashtable, which represents a binding from the names of query variables to terms within the solution. |
java.util.Hashtable[] |
nSolutions(long n)
calls the Query's goal to exhaustion or until N solutions are found, whichever is sooner, and returns an array containing (as possibly empty Hashtables of variablename-to-term bindings) every found solution (in the order in which they were found). |
static java.util.Hashtable[] |
nSolutions(java.lang.String text,
long n)
This static method creates a Query from the given Prolog source text fragment, calls it to exhaustion or until N solutions are found, whichever is sooner, and returns an array containing (as possibly empty Hashtables of variablename-to-term bindings) every found solution (in the order in which they were found). |
static java.util.Hashtable[] |
nSolutions(java.lang.String text,
Term[] params,
long n)
If text denotes (in traditional Prolog source syntax) a term containing N questionmark (?) symbols and there are N accompanying params, this static method replaces each questionmark symbol by its respective param, calls the resulting goal to exhaustion or until N solutions are found, whichever is sooner, and returns an array containing (as possibly empty Hashtables of variablename-to-term bindings) every found solution (in the order in which they were found). |
static java.util.Hashtable[] |
nSolutions(Term goal,
long n)
This static method creates a Query whose goal is the given Term, calls it to exhaustion or until N solutions are found, whichever is sooner, and returns an array containing (as possibly empty Hashtables of variablename-to-term bindings) every found solution (in the order in which they were found). |
java.util.Hashtable |
oneSolution()
Returns the first solution, if any, as a (possibly empty) Hashtable of variablename-to-term bindings, else null. |
static java.util.Hashtable |
oneSolution(java.lang.String text)
This static method creates a Query from the given Prolog source text fragment, and calls it at most once, returning the first solution, if there is one, as a (possibly empty) Hashtable, else null. |
static java.util.Hashtable |
oneSolution(java.lang.String text,
Term[] params)
If text denotes (in traditional Prolog source syntax) a term containing N questionmark (?) symbols and there are N params, each questionmark symbol is replaced by its respective param to provide the goal of this query: the resulting goal is then called (at most once) and the first solution, if there is one, is returned as a (possibly empty) Hashtable, else null. |
static java.util.Hashtable |
oneSolution(Term goal)
This static method creates a Query (whose goal is the specified Term) and calls it at most once, returning the first solution, if there is one, as a (possibly empty) Hashtable, else null. |
void |
open()
This method returns true if JPL was able to initiate a "call" of this Query within the Prolog engine. |
boolean |
query()
Deprecated. Use .hasSolution() instead. |
void |
rewind()
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java.lang.String |
toString()
Returns a crude String representation of a Query. |
Methods inherited from class java.lang.Object |
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equals, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Constructor Detail |
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public Query(Term t)
t
- the goal of this Querypublic Query(java.lang.String text, Term[] args)
text
- the name of the principal functor of this Query's goalargs
- the arguments of this Query's goalpublic Query(java.lang.String text, Term arg)
public Query(java.lang.String text)
text
- the Prolog source text of this QueryMethod Detail |
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public final java.lang.String name()
public final Term[] args()
public final Compound goal()
public final boolean isOpen()
public final boolean hasMoreSolutions()
Query q = // obtain Query reference while (q.hasMoreSolutions()) { Hashtable solution = q.nextSolution(); // process solution... }To ensure thread-safety, you should wrap sequential calls to this method in a synchronized block, using the static lock method to obtain the monitor.
Query q = // obtain Query reference synchronized ( jpl.Query.lock() ){ while ( q.hasMoreElements() ){ Hashtable solution = q.nextSolution(); // process solution... } }
public final void open()
Query q = // obtain Query reference Hashtable soln; q.open(); while ((soln = q.getSolution()) != null) { // process solution... }
If this method is called on an already-open Query, or if the query cannot be set up for whatever reason, then a JPLException will be thrown.
public final java.util.Hashtable getSolution()
For example, if a Query has an occurrence of a jpl.Variable, say, named "X", one can obtain the Term bound to "X" in the solution by looking up "X" in the Hashtable.
Variable x = new Variable("X"); Query q = // obtain Query reference (with x in the Term array) while (q.hasMoreSolutions()) { Hashtable solution = q.nextSolution(); // make t the Term bound to "X" in the solution Term t = (Term) solution.get("X"); // ... }Programmers should obey the following rules when using this method. This method will throw a JPLException if Query is not open.
public final java.util.Hashtable getSubstWithNameVars()
public final java.util.Hashtable nextSolution()
For example, if a Query has an occurrence of a jpl.Variable, say, named "X", one can obtain the Term bound to "X" in the solution by looking up "X" in the Hashtable.
Variable x = new Variable("X"); Query q = // obtain Query reference (with x in the Term array) while (q.hasMoreSolutions()) { Hashtable solution = q.nextSolution(); // make t the Term bound to "X" in the solution Term t = (Term) solution.get("X"); // ... }Programmers should obey the following rules when using this method. This method will throw a JPLException if Query is not open.
public final boolean hasMoreElements()
hasMoreElements
in interface java.util.Enumeration
public final java.lang.Object nextElement()
nextElement
in interface java.util.Enumeration
public final void rewind()
public final void close()
Here is one way to get the first three solutions to a Query:
Query q = new Query(predicate, args); Hashtable sub1 = (Hashtable) q.nextSolution(); Hashtable sub2 = (Hashtable) q.nextSolution(); Hashtable sub3 = (Hashtable) q.nextSolution(); q.close();
public final java.util.Hashtable[] allSolutions()
NB in JPL 1.0.1, bindings were keyed (awkwardly) by Variable instances; in JPL 2.x onwards they are keyed by the (String) names of variables, which is consistent with the Term type being just a concrete syntax for terms (and hence queries).
public static final java.util.Hashtable[] allSolutions(Term goal)
goal
- the goal of this Query
public static final java.util.Hashtable[] allSolutions(java.lang.String text)
text
- a Prolog source text fragment denoting a goal
public static final java.util.Hashtable[] allSolutions(java.lang.String text, Term[] params)
text
- the Prolog source text of a goal, in which questionmarks are regarded as substitutible parametersparams
- terms to be substituted for the respective questionmarks in the query text
public final java.util.Hashtable[] nSolutions(long n)
NB in JPL 1.0.1, bindings were keyed (awkwardly) by Variable instances; in JPL 2.x onwards they are keyed by the (String) names of variables, which is consistent with the Term type being just a concrete syntax for terms (and hence queries).
public static final java.util.Hashtable[] nSolutions(Term goal, long n)
goal
- the goal of this Querypublic static final java.util.Hashtable[] nSolutions(java.lang.String text, long n)
text
- a Prolog source text fragment denoting a goalpublic static final java.util.Hashtable[] nSolutions(java.lang.String text, Term[] params, long n)
text
- the Prolog source text of a goal, in which questionmarks are regarded as substitutible parametersparams
- terms to be substituted for the respective questionmarks in the query textpublic final java.util.Hashtable oneSolution()
public static final java.util.Hashtable oneSolution(Term goal)
goal
- the goal of this Querypublic static final java.util.Hashtable oneSolution(java.lang.String text)
text
- a Prolog source text fragment denoting a goalpublic static final java.util.Hashtable oneSolution(java.lang.String text, Term[] params)
text
- the Prolog source text of a goal, in which questionmarks are regarded as substitutible parametersparams
- terms to be substituted for the respective questionmarks in the query textpublic final boolean query()
Only the first solution (if there is one) will be found; any bindings will be discarded, and the Query will be closed.
This method will throw a JPLException if this Query is already open.
public final boolean hasSolution()
Only the first solution (if there is one) will be found; any bindings will be discarded, and the Query will be closed.
This method will throw a JPLException if this Query is already open.
public static final boolean hasSolution(Term goal)
goal
- the goal of this Querypublic static final boolean hasSolution(java.lang.String text)
text
- the goal of this Query, as Prolog source textpublic static final boolean hasSolution(java.lang.String text, Term[] params)
text
- the Prolog source text of a goal, in which questionmarks are regarded as substitutible parametersparams
- terms to be substituted for the respective questionmarks in the query textpublic final int abort()
public java.lang.String toString()
toString
in class java.lang.Object
public java.lang.String debugString()
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