triple.java

jena2.5.4推理机系统的一种最基本实现 HP实验室出品

/*
  (c) Copyright 2002, 2003, 2004, 2005, 2006, 2007 Hewlett-Packard Development Company, LP
  [See end of file]
  $Id: Triple.java,v 1.26 2007/07/04 15:22:02 chris-dollin Exp $
*/

package com.hp.hpl.jena.graph;

import com.hp.hpl.jena.graph.test.NodeCreateUtils;
import com.hp.hpl.jena.shared.*;
import com.hp.hpl.jena.util.iterator.Filter;

import java.util.*;

/**
    Triples are the basis for RDF statements; they have a subject, predicate, and
    object field (all nodes) and express the notion that the relationship named
    by the predicate holds between the subject and the object.
    
    @author Jeremy Carroll, kers
 */
public class Triple implements TripleMatch 
    {    
	private final Node subj, pred, obj;
    
	public Triple( Node s, Node p, Node o ) 
        {
        if (s == null) throw new UnsupportedOperationException( "subject cannot be null" );
        if (p == null) throw new UnsupportedOperationException( "predicate cannot be null" );
        if (o == null) throw new UnsupportedOperationException( "object cannot be null" );
		subj = s;
		pred = p;
		obj = o;
        }
	
    /**
        return a human-readable string "subject @predicate object" describing the triple
    */
	public String toString()
        { return toString( PrefixMapping.Standard ); }
    
    public String toString( PrefixMapping pm )
       {
	   return subj.toString( pm, true ) 
            + " @" + pred.toString( pm, true ) 
            + " " + obj.toString( pm, true );
	   }
    
    /**
        @return the subject of the triple
    */
	public final Node getSubject() 
        { return subj; }
    
    /**
        @return the predicate of the triple
    */
	public final Node getPredicate() 
        { return pred; }
    
    /**
        @return the object of the triple
    */
	public final Node getObject() 
        { return obj; }

    public Node getMatchSubject()
        { return anyToNull( subj ); }
        
    public Node getMatchPredicate()
        { return anyToNull( pred ); }
        
    public Node getMatchObject()
        { return anyToNull( obj ); }
        
    private static Node anyToNull( Node n )
        { return Node.ANY.equals( n ) ? null : n; }

    private static Node nullToAny( Node n )
        { return n == null ? Node.ANY : n; }        
        
    public Triple asTriple()
        { return this; }
        
    public boolean isConcrete()
        { return subj.isConcrete() && pred.isConcrete() && obj.isConcrete(); }
        
    /** 
         Answer true if <code>o</code> is a Triple with the same subject, predicate,
         and object as this triple.
    */
	public boolean equals(Object o) 
        { return o instanceof Triple && ((Triple) o).sameAs( subj, pred, obj ); }
    
    /** 
        Answer true iff this triple has subject s, predicate p, and object o.
    */    
    public boolean sameAs( Node s, Node p, Node o )
        { return subj.equals( s ) && pred.equals( p ) && obj.equals( o ); }
        
    public boolean matches( Triple other )
        { return other.matchedBy( subj, pred, obj  ); }
        
    public boolean matches( Node s, Node p, Node o )
        { return subj.matches( s ) && pred.matches( p ) && obj.matches( o ); }
        
    private boolean matchedBy( Node s, Node p, Node o )
        { return s.matches( subj ) && p.matches( pred ) && o.matches( obj ); }
        
    public boolean subjectMatches( Node s )
        { return subj.matches( s ); }
        
    public boolean predicateMatches( Node p )
        { return pred.matches( p ); }
        
    public boolean objectMatches( Node o )
        { return obj.matches( o ); }
        
    /**
        The hash-code of a triple is the hash-codes of its components munged
        together: see hashCode(S, P, O).
    */
    public int hashCode() 
        { return hashCode( subj, pred, obj ); }
    
    /**
        Return the munged hashCodes of the specified nodes, an exclusive-or of 
        the slightly-shifted component hashcodes; this means (almost) all of the bits 
        count, and the order matters, so (S @P O) has a different hash from 
        (O @P S), etc.
    */    
    public static int hashCode( Node s, Node p, Node o ) 
        { return (s.hashCode() >> 1) ^ p.hashCode() ^ (o.hashCode() << 1); }
    
    /**
        Factory method for creating triples, allows caching opportunities. Attempts
        to use triples from the cache, if any suitable ones exist.
        
        @return a triple with subject=s, predicate=p, object=o
    */
    public static Triple create( Node s, Node p, Node o )
        { 
        Triple already = cache.get( s, p, o );
        return already == null ? cache.put( new Triple( s, p, o ) ) : already;
        }
    
    /**
        The cache of already-created triples.
    */
    protected static TripleCache cache = new TripleCache();
        
    public static Triple createMatch( Node s, Node p, Node o )
        { return Triple.create( nullToAny( s ), nullToAny( p ), nullToAny( o ) ); }
        
    /**
        Utility factory method for creating a triple based on the content of an
        "S P O" string. The S, P, O are processed by Node.create, see which for
        details of the supported syntax. This method exists to support test code.
        Nodes are interpreted using the Standard prefix mapping.
    */
    
    public static Triple create( String fact )
        { return create( PrefixMapping.Standard, fact ); }
        
    /**
        Utility factory as for create(String), but allowing the PrefixMapping to
        be specified explicitly.
    */
    public static Triple create( PrefixMapping pm, String fact )
        {
        StringTokenizer st = new StringTokenizer( fact );
        Node sub = NodeCreateUtils.create( pm, st.nextToken() );
        Node pred = NodeCreateUtils.create( pm, st.nextToken() );
        Node obj = NodeCreateUtils.create( pm, st.nextToken() );
        return Triple.create( sub, pred, obj );
        }

    /**
        A Triple that is wildcarded in all fields. 
    */
    public static final Triple ANY = Triple.create( Node.ANY, Node.ANY, Node.ANY );
    
    /**
        A Field is a selector from Triples; it allows selectors to be passed
        around as if they were functions, hooray. 
    */
    public static abstract class Field
        {
        public abstract Node getField( Triple t );
        
        public abstract Filter filterOn( Node n );
        
        public final Filter filterOn( Triple t )
            { return filterOn( getField( t ) ); }
        
        public static final Field getSubject = new Field() 
            { 
            public Node getField( Triple t ) 
                { return t.subj; }
            
            public Filter filterOn( final Node n )
                { 
                return n.isConcrete() 
                    ? new Filter() 
                        { public boolean accept( Object x ) { return n.equals( ((Triple) x).subj ); } }
                    : Filter.any
                    ;
                }
            };
            
        public static final Field getObject = new Field() 
            { 
            public Node getField( Triple t ) 
                { return t.obj; } 
            
            public Filter filterOn( final Node n )
                { return n.isConcrete() 
                    ? new Filter() 
                        { public boolean accept( Object x ) 
                            { return n.sameValueAs( ((Triple) x).obj ); } }
                    : Filter.any; 
                }
            };
        
        public static final Field getPredicate = new Field() 
            { 
            public Node getField( Triple t ) 
                { return t.pred; } 
            
            public Filter filterOn( final Node n )
                { return n.isConcrete()
                    ? new Filter() 
                        { public boolean accept( Object x ) { return n.equals( ((Triple) x).pred ); } }
                    : Filter.any; 
                }
            };
        }
    }

/*
    (c) Copyright 2002, 2003, 2004, 2005, 2006, 2007 Hewlett-Packard Development Company, LP
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

    1. Redistributions of source code must retain the above copyright
       notice, this list of conditions and the following disclaimer.

    2. Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in the
       documentation and/or other materials provided with the distribution.

    3. The name of the author may not be used to endorse or promote products
       derived from this software without specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
    IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
    OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
    IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
    NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
    THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/