public final class CollationElementIterator extends Object
CollationElementIterator is an iterator created by
a RuleBasedCollator to walk through a string. The return result of
each iteration is a 32-bit collation element (CE) that defines the
ordering priority of the next character or sequence of characters
in the source string.
For illustration, consider the following in Slovak and in traditional Spanish collation:
"ca" -> the first collation element is CE('c') and the second
collation element is CE('a').
"cha" -> the first collation element is CE('ch') and the second
collation element is CE('a').
And in German phonebook collation,
Since the character 'æ' is a composed character of 'a' and 'e', the
iterator returns two collation elements for the single character 'æ'
"æb" -> the first collation element is collation_element('a'), the
second collation element is collation_element('e'), and the
third collation element is collation_element('b').
For collation ordering comparison, the collation element results
can not be compared simply by using basic arithmetic operators,
e.g. <, == or >, further processing has to be done. Details
can be found in the ICU
User Guide. An example of using the CollationElementIterator
for collation ordering comparison is the class
StringSearch.
To construct a CollationElementIterator object, users call the method getCollationElementIterator() on a RuleBasedCollator that defines the desired sorting order.
Example:
String testString = "This is a test";
RuleBasedCollator rbc = new RuleBasedCollator("&a<b");
CollationElementIterator iterator = rbc.getCollationElementIterator(testString);
int primaryOrder = iterator.IGNORABLE;
while (primaryOrder != iterator.NULLORDER) {
int order = iterator.next();
if (order != iterator.IGNORABLE &&
order != iterator.NULLORDER) {
// order is valid, not ignorable and we have not passed the end
// of the iteration, we do something
primaryOrder = CollationElementIterator.primaryOrder(order);
System.out.println("Next primary order 0x" +
Integer.toHexString(primaryOrder));
}
}
The method next() returns the collation order of the next character based on the comparison level of the collator. The method previous() returns the collation order of the previous character based on the comparison level of the collator. The Collation Element Iterator moves only in one direction between calls to reset(), setOffset(), or setText(). That is, next() and previous() can not be inter-used. Whenever previous() is to be called after next() or vice versa, reset(), setOffset() or setText() has to be called first to reset the status, shifting current position to either the end or the start of the string (reset() or setText()), or the specified position (setOffset()). Hence at the next call of next() or previous(), the first or last collation order, or collation order at the specified position will be returned. If a change of direction is done without one of these calls, the result is undefined.
This class is not subclassable.
Collator,
RuleBasedCollator,
StringSearch| Modifier and Type | Field and Description |
|---|---|
static int |
IGNORABLE
This constant is returned by the iterator in the methods
next() and previous() when a collation element result is to be
ignored.
|
static int |
NULLORDER
This constant is returned by the iterator in the methods
next() and previous() when the end or the beginning of the
source string has been reached, and there are no more valid
collation elements to return.
|
| Modifier and Type | Method and Description |
|---|---|
boolean |
equals(Object that)
Tests that argument object is equals to this CollationElementIterator.
|
int |
getMaxExpansion(int ce)
Returns the maximum length of any expansion sequence that ends with
the specified collation element.
|
int |
getOffset()
Returns the character offset in the source string
corresponding to the next collation element.
|
int |
hashCode()
Mock implementation of hashCode().
|
int |
next()
Get the next collation element in the source string.
|
int |
previous()
Get the previous collation element in the source string.
|
static int |
primaryOrder(int ce)
Return the primary order of the specified collation element,
i.e.
|
void |
reset()
Resets the cursor to the beginning of the string.
|
static int |
secondaryOrder(int ce)
Return the secondary order of the specified collation element,
i.e.
|
void |
setOffset(int newOffset)
Sets the iterator to point to the collation element
corresponding to the character at the specified offset.
|
void |
setText(CharacterIterator source)
Set a new source string iterator for iteration, and reset the
offset to the beginning of the text.
|
void |
setText(String source)
Set a new source string for iteration, and reset the offset
to the beginning of the text.
|
void |
setText(UCharacterIterator source)
Set a new source string iterator for iteration, and reset the
offset to the beginning of the text.
|
static int |
tertiaryOrder(int ce)
Return the tertiary order of the specified collation element, i.e.
|
public static final int NULLORDER
See class documentation for an example of use.
public static final int IGNORABLE
See class documentation for an example of use.
public static final int primaryOrder(int ce)
ce - the collation elementpublic static final int secondaryOrder(int ce)
ce - the collation elementpublic static final int tertiaryOrder(int ce)
ce - the collation elementpublic int getOffset()
setOffset(offset) sets the index in the middle of
a contraction, getOffset() returns the index of
the first character in the contraction, which may not be equal
to the original offset that was set. Hence calling getOffset()
immediately after setOffset(offset) does not guarantee that the
original offset set will be returned.)
public int next()
This iterator iterates over a sequence of collation elements that were built from the string. Because there isn't necessarily a one-to-one mapping from characters to collation elements, this doesn't mean the same thing as "return the collation element [or ordering priority] of the next character in the string".
This function returns the collation element that the iterator is currently pointing to, and then updates the internal pointer to point to the next element.
public int previous()
This iterator iterates over a sequence of collation elements that were built from the string. Because there isn't necessarily a one-to-one mapping from characters to collation elements, this doesn't mean the same thing as "return the collation element [or ordering priority] of the previous character in the string".
This function updates the iterator's internal pointer to point to the collation element preceding the one it's currently pointing to and then returns that element, while next() returns the current element and then updates the pointer.
public void reset()
If the RuleBasedCollator used by this iterator has had its attributes changed, calling reset() will reinitialize the iterator to use the new attributes.
public void setOffset(int newOffset)
If offset is in the middle of a contracting character sequence, the iterator is adjusted to the start of the contracting sequence. This means that getOffset() is not guaranteed to return the same value set by this method.
If the decomposition mode is on, and offset is in the middle of a decomposible range of source text, the iterator may not return a correct result for the next forwards or backwards iteration. The user must ensure that the offset is not in the middle of a decomposible range.
newOffset - the character offset into the original source string to
set. Note that this is not an offset into the corresponding
sequence of collation elements.public void setText(String source)
source - the new source string for iteration.public void setText(UCharacterIterator source)
The source iterator's integrity will be preserved since a new copy will be created for use.
source - the new source string iterator for iteration.public void setText(CharacterIterator source)
source - the new source string iterator for iteration.public int getMaxExpansion(int ce)
ce - a collation element returned by previous() or next().public boolean equals(Object that)