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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package java.text;
/**
* Represents a string under the rules of a specific {@code Collator} object.
* Comparing two {@code CollationKey} instances returns the relative order of
* the strings they represent.
* <p>
* Since the rule set of collators can differ, the sort orders of the same
* string under two different {@code Collator} instances might differ. Hence
* comparing collation keys generated from different {@code Collator} instances
* can give incorrect results.
* <p>
* Both the method {@code CollationKey.compareTo(CollationKey)} and the method
* {@code Collator.compare(String, String)} compares two strings and returns
* their relative order. The performance characteristics of these two approaches
* can differ.
* <p>
* During the construction of a {@code CollationKey}, the entire source string
* is examined and processed into a series of bits terminated by a null, that
* are stored in the {@code CollationKey}. When
* {@code CollationKey.compareTo(CollationKey)} executes, it performs bitwise
* comparison on the bit sequences. This can incur startup cost when creating
* the {@code 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.
* <p>
* On the other hand, implementations of
* {@code Collator.compare(String, String)} can examine and process the strings
* only until the first characters differ in order. This approach is
* recommended if the strings are to be compared only once.
* <p>
* The following example shows how collation keys can be used to sort a
* list of strings:
* <blockquote>
*
* <pre>
* // 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);
* <br>
* //...
* <br>
* // Inside body of sort routine, compare keys this way
* if( keys[i].compareTo( keys[j] ) > 0 )
* // swap keys[i] and keys[j]
* <br>
* //...
* <br>
* // 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());
* </pre>
*
* </blockquote>
*
* @see Collator
* @see RuleBasedCollator
*/
public abstract class CollationKey implements Comparable<CollationKey> {
private final String source;
protected CollationKey(String source) {
this.source = source;
}
/**
* Compares this collation key to the given collation key.
*
* @param value the other collation key.
* @return a negative value if this key is less than {@code value},
* 0 if they are equal, and a positive value if this key is greater.
*/
public abstract int compareTo(CollationKey value);
/**
* Returns the string from which this collation key was created.
*
* @return the source string of this collation key.
*/
public String getSourceString() {
return source;
}
/**
* Returns this collation key as a byte array.
*
* @return an array of bytes.
*/
public abstract byte[] toByteArray();
}
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