AlphabeticIndex

Kotlin |Java

class AlphabeticIndex<V : Any!> : MutableIterable<AlphabeticIndex.Bucket<V>!>

kotlin.Any
↳	android.icu.text.AlphabeticIndex

AlphabeticIndex supports the creation of a UI index appropriate for a given language. It can support either direct use, or use with a client that doesn't support localized collation. The following is an example of what an index might look like in a UI:

<b>... A B C D E F G H I J K L M N O P Q R S T U V W X Y Z  ...</b><b>A</b>Addison
      Albertson
      Azensky
   <b>B</b>Baecker
   ...

The class can generate a list of labels for use as a UI "index", that is, a list of clickable characters (or character sequences) that allow the user to see a segment (bucket) of a larger "target" list. That is, each label corresponds to a bucket in the target list, where everything in the bucket is greater than or equal to the character (according to the locale's collation). Strings can be added to the index; they will be in sorted order in the right bucket.

The class also supports having buckets for strings before the first (underflow), after the last (overflow), and between scripts (inflow). For example, if the index is constructed with labels for Russian and English, Greek characters would fall into an inflow bucket between the other two scripts.

Note: If you expect to have a lot of ASCII or Latin characters as well as characters from the user's language, then it is a good idea to call addLabels(ULocale.English).

Direct Use

The following shows an example of building an index directly. The "show..." methods below are just to illustrate usage.

// Create a simple index where the values for the strings are Integers, and add the strings
 
  AlphabeticIndex<Integer> index = new AlphabeticIndex<Integer>(desiredLocale).addLabels(additionalLocale);
  int counter = 0;
  for (String item : test) {
      index.addRecord(item, counter++);
  }
  ...
  // Show index at top. We could skip or gray out empty buckets
 
  for (AlphabeticIndex.Bucket<Integer> bucket : index) {
      if (showAll || bucket.size() != 0) {
          showLabelAtTop(UI, bucket.getLabel());
      }
  }
   ...
  // Show the buckets with their contents, skipping empty buckets
 
  for (AlphabeticIndex.Bucket<Integer> bucket : index) {
      if (bucket.size() != 0) {
          showLabelInList(UI, bucket.getLabel());
          for (AlphabeticIndex.Record<Integer> item : bucket) {
              showIndexedItem(UI, item.getName(), item.getData());
          }

The caller can build different UIs using this class. For example, an index character could be omitted or grayed-out if its bucket is empty. Small buckets could also be combined based on size, such as:

<b>... A-F G-N O-Z ...</b>

Client Support

Callers can also use the AlphabeticIndex.ImmutableIndex, or the AlphabeticIndex itself, to support sorting on a client that doesn't support AlphabeticIndex functionality.

The ImmutableIndex is both immutable and thread-safe. The corresponding AlphabeticIndex methods are not thread-safe because they "lazily" build the index buckets.

ImmutableIndex.getBucket(index) provides random access to all buckets and their labels and label types.
AlphabeticIndex.getBucketLabels() or the bucket iterator on either class can be used to get a list of the labels, such as "...", "A", "B",..., and send that list to the client.

When the client has a new name, it sends that name to the server. The server needs to call the following methods, and communicate the bucketIndex and collationKey back to the client.

int bucketIndex = index.getBucketIndex(name);
  String label = immutableIndex.getBucket(bucketIndex).getLabel();  // optional
  RawCollationKey collationKey = collator.getRawCollationKey(name, null);

The client would put the name (and associated information) into its bucket for bucketIndex. The collationKey is a sequence of bytes that can be compared with a binary compare, and produce the right localized result.

Summary

Nested classes
	`Bucket` An index "bucket" with a label string and type.
	`ImmutableIndex` Immutable, thread-safe version of `AlphabeticIndex`.
	`Record` A (name, data) pair, to be sorted by name into one of the index buckets.

Public constructors
`AlphabeticIndex(locale: ULocale!)` Create the index object.
`AlphabeticIndex(locale: Locale!)` Create the index object.
`AlphabeticIndex(collator: RuleBasedCollator!)` Create an AlphabeticIndex that uses a specific collator.

Public methods
AlphabeticIndex<V>!	`addLabels(additions: UnicodeSet!)` Add more index characters (aside from what are in the locale)
AlphabeticIndex<V>!	`addLabels(vararg additions: ULocale!)` Add more index characters (aside from what are in the locale)
AlphabeticIndex<V>!	`addLabels(vararg additions: Locale!)` Add more index characters (aside from what are in the locale)
AlphabeticIndex<V>!	`addRecord(name: CharSequence!, data: V)` Add a record (name and data) to the index.
AlphabeticIndex.ImmutableIndex<V>!	`buildImmutableIndex()` Builds an immutable, thread-safe version of this instance, without data records.
AlphabeticIndex<V>!	`clearRecords()` Clear the index.
Int	`getBucketCount()` Return the number of buckets in the index.
Int	`getBucketIndex(name: CharSequence!)` Get the bucket number for the given name.
MutableList<String!>!	`getBucketLabels()` Get the labels.
RuleBasedCollator!	`getCollator()` Get a clone of the collator used internally.
String!	`getInflowLabel()` Get the default label used for abbreviated buckets between other labels.
Int	`getMaxLabelCount()` Get the limit on the number of labels in the index.
String!	`getOverflowLabel()` Get the default label used in the IndexCharacters' locale for overflow, eg the first item in: .
Int	`getRecordCount()` Return the number of records in the index: that is, the total number of distinct <name,data> pairs added with addRecord(...), over all the buckets.
String!	`getUnderflowLabel()` Get the default label used in the IndexCharacters' locale for underflow, eg the last item in: X Y Z .
MutableIterator<AlphabeticIndex.Bucket<V>!>	`iterator()` Return an iterator over the buckets.
AlphabeticIndex<V>!	`setInflowLabel(inflowLabel: String!)` Set the inflowLabel label
AlphabeticIndex<V>!	`setMaxLabelCount(maxLabelCount: Int)` Set a limit on the number of labels in the index.
AlphabeticIndex<V>!	`setOverflowLabel(overflowLabel: String!)` Set the overflow label
AlphabeticIndex<V>!	`setUnderflowLabel(underflowLabel: String!)` Set the underflowLabel label

Parameters
`name`	CharSequence!: Name, such as a name
`data`	V: Data, such as an address or link

AlphabeticIndex

Direct Use

Client Support

Summary

Public constructors