org.apache.commons.rdf.api

Interface Quad

All Superinterfaces:

QuadLike<BlankNodeOrIRI>, TripleLike

All Known Subinterfaces:

JenaQuad, JsonLdQuad, RDF4JQuad

public interface Quad
extends QuadLike<BlankNodeOrIRI>

A Quad is a statement in a RDF-1.1 Dataset, as defined by RDF-1.1 Concepts and Abstract Syntax, a W3C Working Group Note published on 25 February 2014.

A Quad object in Commons RDF is considered immutable, that is, over its life time it will have consistent behaviour for its equals(Object), and the instances returned from getGraphName(), getSubject(), getPredicate(), getObject() and asTriple() will have consistent Object.equals(Object) behaviour.

Note that Quad methods are not required to return object identical (==) instances as long as they are equivalent according to Object.equals(Object). Specialisations of Quad may provide additional methods that are documented to be mutable.

Quad methods are thread-safe, however specialisations may provide additional methods that are documented to not be thread-safe.

Quads can be safely used in hashing collections like HashSet and HashMap.

Any Quad can be used interchangeably across Commons RDF implementations.

Since:

0.3.0-incubating

See Also:

Dataset, RDF.createQuad(BlankNodeOrIRI,BlankNodeOrIRI,IRI,RDFTerm), RDF 1.1: On Semantics of RDF Datasets,

Method Summary

Modifier and Type	Method and Description
default Triple	asTriple() Adapt this Quad to a Triple.
boolean	equals(Object other) Check it this Quad is equal to another Quad.
Optional<BlankNodeOrIRI>	getGraphName() The graph name (graph label) of this quad, if present.
RDFTerm	getObject() The object of this quad, which may be either a BlankNode, an IRI, or a Literal, which are represented in Commons RDF by the interface RDFTerm.
IRI	getPredicate() The predicate IRI of this quad.
BlankNodeOrIRI	getSubject() The subject of this quad, which may be either a BlankNode or an IRI, which are represented in Commons RDF by the interface BlankNodeOrIRI.
int	hashCode() Calculate a hash code for this Quad.

Method Detail

getGraphName

Optional<BlankNodeOrIRI> getGraphName()

The graph name (graph label) of this quad, if present. If Optional.isPresent(), then the Optional.get() is either a BlankNode or an IRI, indicating the graph name of this Quad. If the graph name is not present, e.g. the value is Optional.empty(), it indicates that this Quad is in the default graph.

Specified by:

getGraphName in interface QuadLike<BlankNodeOrIRI>

Returns:

If Optional.isPresent(), the graph name BlankNodeOrIRI of this quad, otherwise Optional.empty(), indicating the default graph.

See Also:

RDF- 1.1 Dataset

getSubject

BlankNodeOrIRI getSubject()

The subject of this quad, which may be either a BlankNode or an IRI, which are represented in Commons RDF by the interface BlankNodeOrIRI.

Specified by:

getSubject in interface TripleLike

Returns:

The subject BlankNodeOrIRI of this quad.

See Also:

RDF-1.1 Triple subject

getPredicate

IRI getPredicate()

The predicate IRI of this quad.

Specified by:

getPredicate in interface TripleLike

Returns:

The predicate IRI of this quad.

See Also:

RDF-1.1 Triple predicate

getObject

RDFTerm getObject()

The object of this quad, which may be either a BlankNode, an IRI, or a Literal, which are represented in Commons RDF by the interface RDFTerm.

Specified by:

getObject in interface TripleLike

Returns:

The object RDFTerm of this quad.

See Also:

RDF-1.1 Triple object

asTriple

default Triple asTriple()

Adapt this Quad to a Triple.

The returned Triple will have equivalent values returned from the methods TripleLike.getSubject(), TripleLike.getPredicate() and TripleLike.getObject().

The returned Triple MUST NOT be equals(Object) to this Quad, even if this quad has a default graph getGraphName() value of Optional.empty(), but MUST follow the Triple.equals(Object) semantics. This means that the following MUST be true:

 Quad q1, q2;
 if (q1.equals(q2)) {
     assert (q1.asTriple().equals(q2.asTriple()));
 } else if (q1.asTriple().equals(q2.asTriple())) {
     assert (q1.getSubject().equals(q2.getSubject()));
     assert (q1.getPredicate().equals(q2.getPredicate()));
     assert (q1.getObject().equals(q2.getObject()));
     assert (!q1.getGraphName().equals(q2.getGraphName()));
 }
 

The default implementation of this method return a proxy Triple instance that keeps a reference to this Quad to call the underlying TripleLike methods, but supplies a Triple compatible implementation of Triple.equals(Object) and Triple.hashCode(). Implementations may override this method, e.g. for a more efficient solution.

Returns:

A Triple that contains the same TripleLike properties as this Quad.

equals

boolean equals(Object other)

Check it this Quad is equal to another Quad.

Two Quads are equal if and only if their getGraphName(), getSubject(), getPredicate() and getObject() are equal.

Implementations MUST also override hashCode() so that two equal Quads produce the same hash code.

Note that a Quad MUST NOT be equal to a Triple, even if this Quad's getGraphName() is Optional.empty(). To test triple-like equivalence, callers can use:

 Quad q1;
 Triple t2;
 q1.asTriple().equals(t2));
 

Overrides:

equals in class Object

Parameters:

other - Another object

Returns:

true if other is a Quad and is equal to this

See Also:

Object.equals(Object)

hashCode

int hashCode()

Calculate a hash code for this Quad.

The returned hash code MUST be equal to the result of Objects.hash(Object...) with the arguments getSubject(), getPredicate(), getObject(), getGraphName().

This method MUST be implemented in conjunction with equals(Object) so that two equal Quads produce the same hash code.

Overrides:

hashCode in class Object

Returns:

a hash code value for this Quad.

See Also:

Object.hashCode(), Objects.hash(Object...)