public interface RDFList extends Resource
Provides a convenience encapsulation for lists formed from chains of RDF statements arranged to form a head/tail cons-cell structure. The properties that form the links between cells, and from cells to values, are specified by a vocabulary interface, so this abstraction is designed to cope equally well with DAML lists, RDF lists, and user-defined lists.
A well-formed list has cells that are made up of three statements: one
denoting the rdf:type
of the list cell, one denoting the link
to the value of the list at that point, and one pointing to the list tail. If
a list cell is not well-formed, list operations may fail in unpredictable
ways. However, to explicitly check that the list is well-formed at all times
is expensive. Therefore the list operates in two modes: in strict
mode, the well-formedness of the list is checked at the start of each list
operation, and an InvalidListException
is thrown if the list is not
well- formed. This ensures that list operations are safe, but will slow down
processing. In non-strict mode, this checking is switched off, but can
be invoked explicitly by clients by calling isValid()
. By default, RDF
lists are processed in non-strict mode.
Modifier and Type | Interface and Description |
---|---|
static interface |
RDFList.ApplyFn
Interface that encapsulates a function to apply to every element in a
list.
|
static interface |
RDFList.ReduceFn
Interface that encapsulates a function to apply to each element of a list
in turn, and passing the result to an accumulator.
|
Modifier and Type | Method and Description |
---|---|
void |
add(RDFNode value)
Add the given value to the end of the list.
|
RDFList |
append(Iterator<? extends RDFNode> nodes)
Answer a new list that is formed by adding each element of this list to
the head of the the list formed from the
given
nodes . |
RDFList |
append(RDFList list)
Answer a new list that is formed by adding each element of this list to
the head of the given
list . |
void |
apply(RDFList.ApplyFn fn)
Apply a function to each value in the list in turn.
|
List<RDFNode> |
asJavaList()
Answer the contents of this RDF list as a Java list of RDFNode values.
|
void |
concatenate(Iterator<? extends RDFNode> nodes)
Add the nodes returned by the given iterator to the end of this list.
|
void |
concatenate(RDFList list)
Change the tail of this list to point to the given list, so that this
list becomes the list of the concatenation of the elements of both lists.
|
RDFList |
cons(RDFNode value)
Return a reference to a new list cell whose head is
value
and whose tail is this list. |
boolean |
contains(RDFNode value)
Answer true if the given node appears as the value of a value of any
of the cells of this list.
|
RDFList |
copy()
Answer a list that contains all of the elements of this list in the same
order, but is a duplicate copy in the underlying model.
|
RDFNode |
get(int i)
Answer the node that is the i'th element of the list, assuming that the
head is item zero.
|
RDFNode |
getHead()
Answer the value that is at the head of the list.
|
boolean |
getStrict()
Answer true lists are operating in strict mode, in which the
well- formedness of the list is checked at every operation.
|
RDFList |
getTail()
Answer the list that is the tail of this list.
|
String |
getValidityErrorMessage()
Answer the error message returned by the last failed validity check,
if any.
|
int |
indexOf(RDFNode value)
Answer the index of the first occurrence of the given value in the list,
or -1 if the value is not in the list.
|
int |
indexOf(RDFNode value,
int start)
Answer the index of the first occurrence of the given value in the list
after index
start , or -1 if the value is not in the list
after the given start point. |
boolean |
isEmpty()
Answer true if this list is the empty list.
|
boolean |
isValid()
Answer true if the list is well-formed, by checking that each node is
correctly typed, and has a head and tail pointer from the correct
vocabulary.
|
ExtendedIterator<RDFNode> |
iterator()
Answer an iterator over the elements of the list.
|
<T> ExtendedIterator<T> |
mapWith(Function<RDFNode,T> fn)
Answer an iterator of the elements of this list, to each of which
the given map function has been applied.
|
Object |
reduce(RDFList.ReduceFn fn,
Object initial)
Apply a function to each value in the list in turn, accumulating the
results in an accumulator.
|
RDFList |
remove(RDFNode val)
Remove the given value from this list.
|
void |
removeAll()
Deprecated.
Replaced by
removeList() |
RDFList |
removeHead()
Remove the value from the head of the list.
|
void |
removeList()
Remove all of the components of this list from the model.
|
RDFNode |
replace(int i,
RDFNode value)
Replace the value at the i'th position in the list with the given value.
|
boolean |
sameListAs(RDFList list)
Answer true if this list has the same elements in the same order as the
given list.
|
RDFNode |
setHead(RDFNode value)
Update the head of the list to have the given value, and return the
previous value.
|
void |
setStrict(boolean strict)
Set a flag to indicate whether to strictly check the well-formedness of
lists at each operation.
|
RDFList |
setTail(RDFList tail)
Update the list cell at the front of the list to have the given list as
tail.
|
int |
size()
Answer the number of elements in the list.
|
RDFList |
with(RDFNode value)
Answer the list that is this list with the given value added to the end
of the list.
|
abort, addLiteral, addLiteral, addLiteral, addLiteral, addLiteral, addLiteral, addLiteral, addProperty, addProperty, addProperty, addProperty, begin, commit, equals, getId, getLocalName, getNameSpace, getProperty, getProperty, getPropertyResourceValue, getRequiredProperty, getRequiredProperty, getURI, hasLiteral, hasLiteral, hasLiteral, hasLiteral, hasLiteral, hasLiteral, hasProperty, hasProperty, hasProperty, hasProperty, hasURI, inModel, listProperties, listProperties, listProperties, removeAll, removeProperties, toString
as, asLiteral, asResource, canAs, getModel, isAnon, isLiteral, isResource, isURIResource, visitWith
asNode
int size()
Answer the number of elements in the list.
RDFNode getHead()
Answer the value that is at the head of the list.
EmptyListException
- if this list is the empty listRDFNode setHead(RDFNode value)
Update the head of the list to have the given value, and return the previous value.
value
- The value that will become the value of the list headEmptyListException
- if this list is the empty listRDFList getTail()
Answer the list that is the tail of this list.
EmptyListException
- if this list is the empty listRDFList setTail(RDFList tail)
Update the list cell at the front of the list to have the given list as tail. The old tail is returned, and remains in the model.
tail
- The new tail for this list.boolean isEmpty()
RDFList cons(RDFNode value)
Return a reference to a new list cell whose head is value
and whose tail is this list.
value
- A new value to add to the head of the listvalue
void add(RDFNode value)
Add the given value to the end of the list. This is a side-effecting
operation on the underlying model that is only defined if this is not the
empty list. If this list is the empty (nil) list, we cannot perform a
side-effecting update without changing the URI of this node (from rdf:nil
)
to a blank-node for the new list cell) without violating a Jena invariant.
Therefore, this update operation will throw an exception if an attempt is
made to add to the nil list. Safe ways to add to an empty list include
with(org.apache.jena.rdf.model.RDFNode)
and cons(org.apache.jena.rdf.model.RDFNode)
.
value
- A value to add to the end of the listEmptyListUpdateException
- if an attempt is made to
add
to the empty list.RDFList with(RDFNode value)
Answer the list that is this list with the given value added to the end
of the list. This operation differs from add(org.apache.jena.rdf.model.RDFNode)
in that it will
always work, even on an empty list, but the return value is the updated
list. Specifically, in the case of adding a value to the empty list, the
returned list will not be the same as this list. Client code should
not assume that this is an in-place update, but should ensure that the resulting
list is asserted back into the graph into the appropriate relationships.
value
- A value to add to the end of the listRDFNode get(int i)
Answer the node that is the i'th element of the list, assuming that the
head is item zero. If the list is too short to have an i'th element,
throws a ListIndexException
.
i
- The index into the list, from 0ListIndexException
- if the list has fewer than (i + 1)
elements.RDFNode replace(int i, RDFNode value)
Replace the value at the i'th position in the list with the given value.
If the list is too short to have an i'th element, throws a ListIndexException
.
i
- The index into the list, from 0value
- The new value to associate with the i'th list elementListIndexException
- if the list has fewer than (i + 1)
elements.boolean contains(RDFNode value)
Answer true if the given node appears as the value of a value of any of the cells of this list.
value
- A value to test forint indexOf(RDFNode value)
Answer the index of the first occurrence of the given value in the list, or -1 if the value is not in the list.
value
- The value to search for-1
if not found.int indexOf(RDFNode value, int start)
Answer the index of the first occurrence of the given value in the list
after index start
, or -1 if the value is not in the list
after the given start point.
value
- The value to search forstart
- The index into the list to start searching fromstart
, or -1
if not found.ListIndexException
- if start
is greater than the
length of the list.RDFList append(RDFList list)
Answer a new list that is formed by adding each element of this list to
the head of the given list
. This is a non side-effecting
operation on either this list or the given list, but generates a copy
of this list. For a more storage efficient alternative, see concatenate
.
list
- The argument listRDFList append(Iterator<? extends RDFNode> nodes)
Answer a new list that is formed by adding each element of this list to
the head of the the list formed from the
given nodes
. This is a non side-effecting
operation on either this list or the given list, but generates a copy
of this list. For a more storage efficient alternative, see concatenate
.
nodes
- An iterator whose range is RDFNodevoid concatenate(RDFList list)
Change the tail of this list to point to the given list, so that this
list becomes the list of the concatenation of the elements of both lists.
This is a side-effecting operation on this list; for a non side-effecting
alternative, see append(org.apache.jena.rdf.model.RDFList)
. Due to the problem of maintaining
the URI invariant on a node, this operation will throw an exception if an
attempt is made to concatenate onto an empty list. To avoid this, test for
an empty list: if true replace the empty list with the argument list, otherwise
proceed with the concatenate as usual. An alternative solution is to use
append(org.apache.jena.rdf.model.RDFList)
and replace the original list with the return value.
list
- The argument list to concatenate to this listEmptyListUpdateException
- if this list is the nil listvoid concatenate(Iterator<? extends RDFNode> nodes)
Add the nodes returned by the given iterator to the end of this list.
nodes
- An iterator whose range is RDFNodeEmptyListUpdateException
- if this list is the nil listfor details on avoiding the empty list update exception.
RDFList copy()
Answer a list that contains all of the elements of this list in the same order, but is a duplicate copy in the underlying model.
void apply(RDFList.ApplyFn fn)
Apply a function to each value in the list in turn.
fn
- The function to apply to each list node.Object reduce(RDFList.ReduceFn fn, Object initial)
Apply a function to each value in the list in turn, accumulating the
results in an accumulator. The final value of the accumulator is returned
as the value of reduce()
.
fn
- The reduction function to applyinitial
- The initial value for the accumulator<T> ExtendedIterator<T> mapWith(Function<RDFNode,T> fn)
Answer an iterator of the elements of this list, to each of which the given map function has been applied.
fn
- A mapping functionRDFList removeHead()
Remove the value from the head of the list. The tail of the list remains
in the model. Note that no changes are made to list cells that point to
this list cell as their tail. Immediately following a
removeHead
operation, such lists will be in a non-valid
state.
@Deprecated void removeAll()
removeList()
Deprecated. Since an RDFList
does not behave like a Java container, it is not
the case that the contents of the list can be removed and the container filled with values
again. Therefore, this method name has been deprecated in favour of removeList()
void removeList()
Remove all of the components of this list from the model. Once this operation
has completed, the RDFList
resource on which it was called will no
longer be a resource in the model, so further methods calls on the list object
(for example, size()
will fail. Due to restrictions on the encoding
of lists in RDF, it is not possible to perform an operation which empties a list
and then adds further values to that list. Client code wishing to perform
such an operation should do so in two steps: first remove the old list, then
create a new list with the new contents. It is important that RDF statements
that reference the old list (in the object position) be updated to point
to the newly created list.
Note that this
is operation is only removing the list cells themselves, not the resources
referenced by the list - unless being the object of an rdf:first
statement is the only mention of that resource in the model.
RDFList remove(RDFNode val)
Remove the given value from this list. If val
does not occur in
the list, no action is taken. Since removing the head of the list will invalidate
the list head cell, in general the list must return the list that results from this
operation. However, in many cases the return value will be the same as the object
that this method is invoked on
val
- The value to be removed from the listval
occurs at the head of the list.ExtendedIterator<RDFNode> iterator()
Answer an iterator over the elements of the list. Note that this iterator
does not take a snapshot of the list, so changes to the list statements
in the model while iterating will affect the behaviour of the iterator.
To get an iterator that is not affected by model changes, use asJavaList()
.
List<RDFNode> asJavaList()
Answer the contents of this RDF list as a Java list of RDFNode values.
boolean sameListAs(RDFList list)
Answer true if this list has the same elements in the same order as the
given list. Note that the standard equals
test just tests
for equality of two given list cells. While such a test is sufficient
for many purposes, this test provides a broader equality definition, but
is correspondingly more expensive to test.
list
- The list to test againstboolean getStrict()
Answer true lists are operating in strict mode, in which the well- formedness of the list is checked at every operation.
void setStrict(boolean strict)
Set a flag to indicate whether to strictly check the well-formedness of lists at each operation. Default false. Note that the flag that is manipulated is actually a static: it applies to all lists. However, RDFList is a Java interface, and Java does not permit static methods in interfaces.
strict
- The static flag for whether lists will be checked strictly.boolean isValid()
Answer true if the list is well-formed, by checking that each node is
correctly typed, and has a head and tail pointer from the correct
vocabulary. If the list is invalid, the reason is available via getValidityErrorMessage()
.
getValidityErrorMessage()
Licenced under the Apache License, Version 2.0