public final class

Bidi

extends Object
java.lang.Object
   ↳ java.text.Bidi

Class Overview

Implements the Unicode Bidirectional Algorithm.

Use a Bidi object to get the information on the position reordering of a bidirectional text, such as Arabic or Hebrew. The natural display ordering of horizontal text in these languages is from right to left, while they order numbers from left to right.

If the text contains multiple runs, the information of each run can be obtained from the run index. The level of any particular run indicates the direction of the text as well as the nesting level. Left-to-right runs have even levels while right-to-left runs have odd levels.

Summary

Constants
int DIRECTION_DEFAULT_LEFT_TO_RIGHT Constant that indicates the default base level.
int DIRECTION_DEFAULT_RIGHT_TO_LEFT Constant that indicates the default base level.
int DIRECTION_LEFT_TO_RIGHT Constant that specifies the default base level as 0 (left-to-right).
int DIRECTION_RIGHT_TO_LEFT Constant that specifies the default base level as 1 (right-to-left).
Public Constructors
Bidi(AttributedCharacterIterator paragraph)
Creates a Bidi object from the AttributedCharacterIterator of a paragraph text.
Bidi(char[] text, int textStart, byte[] embeddings, int embStart, int paragraphLength, int flags)
Creates a Bidi object.
Bidi(String paragraph, int flags)
Creates a Bidi object.
Public Methods
boolean baseIsLeftToRight()
Returns whether the base level is from left to right.
Bidi createLineBidi(int lineStart, int lineLimit)
Creates a new Bidi object containing the information of one line from this object.
int getBaseLevel()
Returns the base level.
int getLength()
Returns the length of the text in the Bidi object.
int getLevelAt(int offset)
Returns the level of a specified character.
int getRunCount()
Returns the number of runs in the bidirectional text.
int getRunLevel(int run)
Returns the level of the specified run.
int getRunLimit(int run)
Returns the limit offset of the specified run.
int getRunStart(int run)
Returns the start offset of the specified run.
boolean isLeftToRight()
Indicates whether the text is from left to right, that is, both the base direction and the text direction is from left to right.
boolean isMixed()
Indicates whether the text direction is mixed.
boolean isRightToLeft()
Indicates whether the text is from right to left, that is, both the base direction and the text direction is from right to left.
static void reorderVisually(byte[] levels, int levelStart, Object[] objects, int objectStart, int count)
Reorders a range of objects according to their specified levels.
static boolean requiresBidi(char[] text, int start, int limit)
Indicates whether a range of characters of a text requires a Bidi object to display properly.
String toString()
Returns a string containing a concise, human-readable description of this object.
[Expand]
Inherited Methods
From class java.lang.Object

Constants

public static final int DIRECTION_DEFAULT_LEFT_TO_RIGHT

Since: API Level 1

Constant that indicates the default base level. If there is no strong character, then set the paragraph level to 0 (left-to-right).

Constant Value: -2 (0xfffffffe)

public static final int DIRECTION_DEFAULT_RIGHT_TO_LEFT

Since: API Level 1

Constant that indicates the default base level. If there is no strong character, then set the paragraph level to 1 (right-to-left).

Constant Value: -1 (0xffffffff)

public static final int DIRECTION_LEFT_TO_RIGHT

Since: API Level 1

Constant that specifies the default base level as 0 (left-to-right).

Constant Value: 0 (0x00000000)

public static final int DIRECTION_RIGHT_TO_LEFT

Since: API Level 1

Constant that specifies the default base level as 1 (right-to-left).

Constant Value: 1 (0x00000001)

Public Constructors

public Bidi (AttributedCharacterIterator paragraph)

Since: API Level 1

Creates a Bidi object from the AttributedCharacterIterator of a paragraph text. The RUN_DIRECTION attribute determines the base direction of the bidirectional text. If it is not specified explicitly, the algorithm uses DIRECTION_DEFAULT_LEFT_TO_RIGHT by default. The BIDI_EMBEDDING attribute specifies the level of embedding for each character. Values between -1 and -62 denote overrides at the level's absolute value, values from 1 to 62 indicate embeddings, and the 0 value indicates the level is calculated by the algorithm automatically. For the character with no BIDI_EMBEDDING attribute or with a improper attribute value, such as a null value, the algorithm treats its embedding level as 0. The NUMERIC_SHAPING attribute specifies the instance of NumericShaper used to convert European digits to other decimal digits before performing the bidi algorithm.

Parameters
paragraph the String containing the paragraph text to perform the algorithm.
Throws
IllegalArgumentException if paragraph == null
See Also

public Bidi (char[] text, int textStart, byte[] embeddings, int embStart, int paragraphLength, int flags)

Since: API Level 1

Creates a Bidi object.

Parameters
text the char array of the paragraph text that is processed.
textStart the index in text of the start of the paragraph.
embeddings the embedding level array of the paragraph text, specifying the embedding level information for each character. Values between -1 and -61 denote overrides at the level's absolute value, values from 1 to 61 indicate embeddings, and the 0 value indicates the level is calculated by the algorithm automatically.
embStart the index in embeddings of the start of the paragraph.
paragraphLength the length of the text to perform the algorithm.
flags indicates the base direction of the bidirectional text. It is expected that this will be one of the direction constant values defined in this class. An unknown value is treated as DIRECTION_DEFAULT_LEFT_TO_RIGHT.
Throws
IllegalArgumentException if textStart, embStart, or paragraphLength is negative; if text.length < textStart + paragraphLength or embeddings.length < embStart + paragraphLength.
See Also

public Bidi (String paragraph, int flags)

Since: API Level 1

Creates a Bidi object.

Parameters
paragraph the string containing the paragraph text to perform the algorithm on.
flags indicates the base direction of the bidirectional text. It is expected that this will be one of the direction constant values defined in this class. An unknown value is treated as DIRECTION_DEFAULT_LEFT_TO_RIGHT.
See Also

Public Methods

public boolean baseIsLeftToRight ()

Since: API Level 1

Returns whether the base level is from left to right.

Returns
  • true if the base level is from left to right.

public Bidi createLineBidi (int lineStart, int lineLimit)

Since: API Level 1

Creates a new Bidi object containing the information of one line from this object.

Parameters
lineStart the start offset of the line.
lineLimit the limit of the line.
Returns
  • the new line Bidi object. In this new object, the indices will range from 0 to (limit - start - 1).
Throws
IllegalArgumentException if lineStart < 0, lineLimit < 0, lineStart > lineLimit or if lineStart is greater than the length of this object's paragraph text.

public int getBaseLevel ()

Since: API Level 1

Returns the base level.

Returns
  • the base level.

public int getLength ()

Since: API Level 1

Returns the length of the text in the Bidi object.

Returns
  • the length.

public int getLevelAt (int offset)

Since: API Level 1

Returns the level of a specified character.

Parameters
offset the offset of the character.
Returns
  • the level.

public int getRunCount ()

Since: API Level 1

Returns the number of runs in the bidirectional text.

Returns
  • the number of runs, at least 1.

public int getRunLevel (int run)

Since: API Level 1

Returns the level of the specified run.

Parameters
run the index of the run.
Returns
  • the level of the run.

public int getRunLimit (int run)

Since: API Level 1

Returns the limit offset of the specified run.

Parameters
run the index of the run.
Returns
  • the limit offset of the run.

public int getRunStart (int run)

Since: API Level 1

Returns the start offset of the specified run.

Parameters
run the index of the run.
Returns
  • the start offset of the run.

public boolean isLeftToRight ()

Since: API Level 1

Indicates whether the text is from left to right, that is, both the base direction and the text direction is from left to right.

Returns
  • true if the text is from left to right; false otherwise.

public boolean isMixed ()

Since: API Level 1

Indicates whether the text direction is mixed.

Returns
  • true if the text direction is mixed; false otherwise.

public boolean isRightToLeft ()

Since: API Level 1

Indicates whether the text is from right to left, that is, both the base direction and the text direction is from right to left.

Returns
  • true if the text is from right to left; false otherwise.

public static void reorderVisually (byte[] levels, int levelStart, Object[] objects, int objectStart, int count)

Since: API Level 1

Reorders a range of objects according to their specified levels. This is a convenience function that does not use a Bidi object. The range of objects at index from objectStart to objectStart + count will be reordered according to the range of levels at index from levelStart to levelStart + count.

Parameters
levels the level array, which is already determined.
levelStart the start offset of the range of the levels.
objects the object array to reorder.
objectStart the start offset of the range of objects.
count the count of the range of objects to reorder.
Throws
IllegalArgumentException if count, levelStart or objectStart is negative; if count > levels.length - levelStart or if count > objects.length - objectStart.

public static boolean requiresBidi (char[] text, int start, int limit)

Since: API Level 1

Indicates whether a range of characters of a text requires a Bidi object to display properly.

Parameters
text the char array of the text.
start the start offset of the range of characters.
limit the limit offset of the range of characters.
Returns
  • true if the range of characters requires a Bidi object; false otherwise.
Throws
IllegalArgumentException if start or limit is negative; start > limit or limit is greater than the length of this object's paragraph text.

public String toString ()

Since: API Level 1

Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression: 

   getClass().getName() + '@' + Integer.toHexString(hashCode())

See Writing a useful toString method if you intend implementing your own toString method.

Returns
  • a printable representation of this object.