CollationKey represents a String
* under the rules of a specific Collator
* object. Comparing two CollationKeys returns the
* relative order of the Strings they represent.
*
* Since the rule set of Collators can differ, the
* sort orders of the same string under two different
* Collators might differ. Hence comparing
* CollationKeys generated from different
* Collators can give incorrect results.
*
Both the method
* CollationKey.compareTo(CollationKey) and the method
* Collator.compare(String, String) compare two strings
* and returns their relative order. The performance characteristics
* of these two approaches can differ.
* Note that collation keys are often less efficient than simply doing comparison.
* For more details, see the ICU User Guide.
*
*
During the construction of a CollationKey, the
* entire source string is examined and processed into a series of
* bits terminated by a null, that are stored in the CollationKey.
* When CollationKey.compareTo(CollationKey) executes, it
* performs bitwise comparison on the bit sequences. This can incurs
* startup cost when creating the CollationKey, but once
* the key is created, binary comparisons are fast. This approach is
* recommended when the same strings are to be compared over and over
* again.
*
*
On the other hand, implementations of
* Collator.compare(String, String) can examine and
* process the strings only until the first characters differing in
* order. This approach is recommended if the strings are to be
* compared only once.
More information about the composition of the bit sequence can * be found in the * * user guide.
* *The following example shows how CollationKeys can be used
* to sort a list of Strings.
*
* // Create an array of CollationKeys for the Strings to be sorted.
* Collator myCollator = Collator.getInstance();
* CollationKey[] keys = new CollationKey[3];
* keys[0] = myCollator.getCollationKey("Tom");
* keys[1] = myCollator.getCollationKey("Dick");
* keys[2] = myCollator.getCollationKey("Harry");
* sort( keys );
*
* //...
*
* // Inside body of sort routine, compare keys this way
* if( keys[i].compareTo( keys[j] ) > 0 )
* // swap keys[i] and keys[j]
*
* //...
*
* // Finally, when we've returned from sort.
* System.out.println( keys[0].getSourceString() );
* System.out.println( keys[1].getSourceString() );
* System.out.println( keys[2].getSourceString() );
*
*
*
* This class is not subclassable
* @see Collator
* @see RuleBasedCollator
* @author Syn Wee Quek
*/
public final class CollationKey implements Comparable If two CollationKeys can be legitimately compared, then one can
* compare the byte arrays of each to obtain the same result, e.g.
* Note: Comparison between CollationKeys
* created by different Collators might return incorrect
* results. See class documentation.
*
* @param target target CollationKey
* @return an integer value. If the value is less than zero this CollationKey
* is less than than target, if the value is zero they are equal, and
* if the value is greater than zero this CollationKey is greater
* than target.
* @exception NullPointerException is thrown if argument is null.
* @see Collator#compare(String, String)
*/
@Override
public int compareTo(CollationKey target)
{
for (int i = 0;; ++i) {
int l = m_key_[i]&0xff;
int r = target.m_key_[i]&0xff;
if (l < r) {
return -1;
} else if (l > r) {
return 1;
} else if (l == 0) {
return 0;
}
}
}
/**
* Compare this CollationKey and the specified Object for
* equality. The collation rules of the Collator that created
* this key are applied.
*
* See note in compareTo(CollationKey) for warnings about
* possible incorrect results.
*
* @param target the object to compare to.
* @return true if the two keys compare as equal, false otherwise.
* @see #compareTo(CollationKey)
* @exception ClassCastException is thrown when the argument is not
* a CollationKey. NullPointerException is thrown when the argument
* is null.
*/
@Override
public boolean equals(Object target)
{
if (!(target instanceof CollationKey)) {
return false;
}
return equals((CollationKey)target);
}
/**
* Compare this CollationKey and the argument target CollationKey for
* equality.
* The collation
* rules of the Collator object which created these objects are applied.
*
* See note in compareTo(CollationKey) for warnings of incorrect results
*
* @param target the CollationKey to compare to.
* @return true if two objects are equal, false otherwise.
* @exception NullPointerException is thrown when the argument is null.
*/
public boolean equals(CollationKey target)
{
if (this == target) {
return true;
}
if (target == null) {
return false;
}
CollationKey other = target;
int i = 0;
while (true) {
if (m_key_[i] != other.m_key_[i]) {
return false;
}
if (m_key_[i] == 0) {
break;
}
i ++;
}
return true;
}
/**
* Returns a hash code for this CollationKey. The hash value is calculated
* on the key itself, not the String from which the key was created. Thus
* if x and y are CollationKeys, then x.hashCode(x) == y.hashCode()
* if x.equals(y) is true. This allows language-sensitive comparison in a
* hash table.
*
* @return the hash value.
*/
@Override
public int hashCode()
{
if (m_hashCode_ == 0) {
if (m_key_ == null) {
m_hashCode_ = 1;
}
else {
int size = m_key_.length >> 1;
StringBuilder key = new StringBuilder(size);
int i = 0;
while (m_key_[i] != 0 && m_key_[i + 1] != 0) {
key.append((char)((m_key_[i] << 8) | (0xff & m_key_[i + 1])));
i += 2;
}
if (m_key_[i] != 0) {
key.append((char)(m_key_[i] << 8));
}
m_hashCode_ = key.toString().hashCode();
}
}
return m_hashCode_;
}
/**
* Produces a bound for the sort order of a given collation key and a
* strength level. This API does not attempt to find a bound for the
* CollationKey String representation, hence null will be returned in its
* place.
*
* Resulting bounds can be used to produce a range of strings that are
* between upper and lower bounds. For example, if bounds are produced
* for a sortkey of string "smith", strings between upper and lower
* bounds with primary strength would include "Smith", "SMITH", "sMiTh".
*
* There are two upper bounds that can be produced. If BoundMode.UPPER
* is produced, strings matched would be as above. However, if a bound
* is produced using BoundMode.UPPER_LONG is used, the above example will
* also match "Smithsonian" and similar.
*
* For more on usage, see example in test procedure
*
* src/com/ibm/icu/dev/test/collator/CollationAPITest/TestBounds.
*
*
* Collation keys produced may be compared using the compare API.
* @param boundType Mode of bound required. It can be BoundMode.LOWER, which
* produces a lower inclusive bound, BoundMode.UPPER, that
* produces upper bound that matches strings of the same
* length or BoundMode.UPPER_LONG that matches strings that
* have the same starting substring as the source string.
* @param noOfLevels Strength levels required in the resulting bound
* (for most uses, the recommended value is PRIMARY). This
* strength should be less than the maximum strength of
* this CollationKey.
* See users guide for explanation on the strength levels a
* collation key can have.
* @return the result bounded CollationKey with a valid sort order but
* a null String representation.
* @exception IllegalArgumentException thrown when the strength level
* requested is higher than or equal to the strength in this
* CollationKey.
* In the case of an Exception, information
* about the maximum strength to use will be returned in the
* Exception. The user can then call getBound() again with the
* appropriate strength.
* @see CollationKey
* @see CollationKey.BoundMode
* @see Collator#PRIMARY
* @see Collator#SECONDARY
* @see Collator#TERTIARY
* @see Collator#QUATERNARY
* @see Collator#IDENTICAL
*/
public CollationKey getBound(int boundType, int noOfLevels)
{
// Scan the string until we skip enough of the key OR reach the end of
// the key
int offset = 0;
int keystrength = Collator.PRIMARY;
if (noOfLevels > Collator.PRIMARY) {
while (offset < m_key_.length && m_key_[offset] != 0) {
if (m_key_[offset ++]
== Collation.LEVEL_SEPARATOR_BYTE) {
keystrength ++;
noOfLevels --;
if (noOfLevels == Collator.PRIMARY
|| offset == m_key_.length || m_key_[offset] == 0) {
offset --;
break;
}
}
}
}
if (noOfLevels > 0) {
throw new IllegalArgumentException(
"Source collation key has only "
+ keystrength
+ " strength level. Call getBound() again "
+ " with noOfLevels < " + keystrength);
}
// READ ME: this code assumes that the values for BoundMode variables
// will not change. They are set so that the enum value corresponds to
// the number of extra bytes each bound type needs.
byte resultkey[] = new byte[offset + boundType + 1];
System.arraycopy(m_key_, 0, resultkey, 0, offset);
switch (boundType) {
case BoundMode.LOWER: // = 0
// Lower bound just gets terminated. No extra bytes
break;
case BoundMode.UPPER: // = 1
// Upper bound needs one extra byte
resultkey[offset ++] = 2;
break;
case BoundMode.UPPER_LONG: // = 2
// Upper long bound needs two extra bytes
resultkey[offset ++] = (byte)0xFF;
resultkey[offset ++] = (byte)0xFF;
break;
default:
throw new IllegalArgumentException(
"Illegal boundType argument");
}
resultkey[offset] = 0;
return new CollationKey(null, resultkey, offset);
}
/**
* Merges this CollationKey with another.
* The levels are merged with their corresponding counterparts
* (primaries with primaries, secondaries with secondaries etc.).
* Between the values from the same level a separator is inserted.
*
* This is useful, for example, for combining sort keys from first and last names
* to sort such pairs.
* See http://www.unicode.org/reports/tr10/#Merging_Sort_Keys
*
* The recommended way to achieve "merged" sorting is by
* concatenating strings with U+FFFE between them.
* The concatenation has the same sort order as the merged sort keys,
* but merge(getSortKey(str1), getSortKey(str2)) may differ from getSortKey(str1 + '\uFFFE' + str2).
* Using strings with U+FFFE may yield shorter sort keys.
*
* For details about Sort Key Features see
* http://userguide.icu-project.org/collation/api#TOC-Sort-Key-Features
*
* It is possible to merge multiple sort keys by consecutively merging
* another one with the intermediate result.
*
* Only the sort key bytes of the CollationKeys are merged.
* This API does not attempt to merge the
* String representations of the CollationKeys, hence null will be returned
* as the result's String representation.
*
* Example (uncompressed):
*
* byte key1[] = collationkey1.toByteArray();
* byte key2[] = collationkey2.toByteArray();
* int key, targetkey;
* int i = 0;
* do {
* key = key1[i] & 0xFF;
* targetkey = key2[i] & 0xFF;
* if (key < targetkey) {
* System.out.println("String 1 is less than string 2");
* return;
* }
* if (targetkey < key) {
* System.out.println("String 1 is more than string 2");
* }
* i ++;
* } while (key != 0 && targetKey != 0);
*
* System.out.println("Strings are equal.");
*
*
* @return CollationKey value in a sequence of big-endian byte bytes
* terminated by a null.
*/
public byte[] toByteArray()
{
int length = getLength() + 1;
byte result[] = new byte[length];
System.arraycopy(m_key_, 0, result, 0, length);
return result;
}
// public other methods -------------------------------------------------
/**
* Compare this CollationKey to another CollationKey. The
* collation rules of the Collator that created this key are
* applied.
*
* 191B1D 01 050505 01 910505 00
* 1F2123 01 050505 01 910505 00
* will be merged as
* 191B1D 02 1F2123 01 050505 02 050505 01 910505 02 910505 00
*
* @param source CollationKey to merge with
* @return a CollationKey that contains the valid merged sort keys
* with a null String representation,
* i.e. new CollationKey(null, merged_sort_keys)
* @exception IllegalArgumentException thrown if source CollationKey
* argument is null or of 0 length.
*/
public CollationKey merge(CollationKey source)
{
// check arguments
if (source == null || source.getLength() == 0) {
throw new IllegalArgumentException(
"CollationKey argument can not be null or of 0 length");
}
// 1 byte extra for the 02 separator at the end of the copy of this sort key,
// and 1 more for the terminating 00.
byte result[] = new byte[getLength() + source.getLength() + 2];
// merge the sort keys with the same number of levels
int rindex = 0;
int index = 0;
int sourceindex = 0;
while (true) {
// copy level from src1 not including 00 or 01
// unsigned issues
while (m_key_[index] < 0 || m_key_[index] >= MERGE_SEPERATOR_) {
result[rindex++] = m_key_[index++];
}
// add a 02 merge separator
result[rindex++] = MERGE_SEPERATOR_;
// copy level from src2 not including 00 or 01
while (source.m_key_[sourceindex] < 0
|| source.m_key_[sourceindex] >= MERGE_SEPERATOR_) {
result[rindex++] = source.m_key_[sourceindex++];
}
// if both sort keys have another level, then add a 01 level
// separator and continue
if (m_key_[index] == Collation.LEVEL_SEPARATOR_BYTE
&& source.m_key_[sourceindex]
== Collation.LEVEL_SEPARATOR_BYTE) {
++index;
++sourceindex;
result[rindex++] = Collation.LEVEL_SEPARATOR_BYTE;
}
else {
break;
}
}
// here, at least one sort key is finished now, but the other one
// might have some contents left from containing more levels;
// that contents is just appended to the result
int remainingLength;
if ((remainingLength = m_length_ - index) > 0) {
System.arraycopy(m_key_, index, result, rindex, remainingLength);
rindex += remainingLength;
}
else if ((remainingLength = source.m_length_ - sourceindex) > 0) {
System.arraycopy(source.m_key_, sourceindex, result, rindex, remainingLength);
rindex += remainingLength;
}
result[rindex] = 0;
assert rindex == result.length - 1;
return new CollationKey(null, result, rindex);
}
// private data members -------------------------------------------------
/**
* Sequence of bytes that represents the sort key
*/
private byte m_key_[];
/**
* Source string this CollationKey represents
*/
private String m_source_;
/**
* Hash code for the key
*/
private int m_hashCode_;
/**
* Gets the length of this CollationKey
*/
private int m_length_;
/**
* Collation key merge seperator
*/
private static final int MERGE_SEPERATOR_ = 2;
// private methods ------------------------------------------------------
/**
* Gets the length of the CollationKey
* @return length of the CollationKey
*/
private int getLength()
{
if (m_length_ >= 0) {
return m_length_;
}
int length = m_key_.length;
for (int index = 0; index < length; index ++) {
if (m_key_[index] == 0) {
length = index;
break;
}
}
m_length_ = length;
return m_length_;
}
}