public final class

Bidi

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

Class Overview

This class implements the Unicode Bidirectional Algorithm.

A Bidi object provides information on the bidirectional reordering of the text used to create it. This is required, for example, to properly display Arabic or Hebrew text. These languages are inherently mixed directional, as they order numbers from left-to-right while ordering most other text from right-to-left.

Once created, a Bidi object can be queried to see if the text it represents is all left-to-right or all right-to-left. Such objects are very lightweight and this text is relatively easy to process.

If there are multiple runs of text, information about the runs can be accessed by indexing to get the start, limit, and level of a run. The level represents both the direction and the 'nesting level' of a directional run. Odd levels are right-to-left, while even levels are left-to-right. So for example level 0 represents left-to-right text, while level 1 represents right-to-left text, and level 2 represents left-to-right text embedded in a right-to-left run.

Summary

Constants
int DIRECTION_DEFAULT_LEFT_TO_RIGHT Constant indicating that the base direction depends on the first strong directional character in the text according to the Unicode Bidirectional Algorithm.
int DIRECTION_DEFAULT_RIGHT_TO_LEFT Constant indicating that the base direction depends on the first strong directional character in the text according to the Unicode Bidirectional Algorithm.
int DIRECTION_LEFT_TO_RIGHT Constant indicating base direction is left-to-right.
int DIRECTION_RIGHT_TO_LEFT Constant indicating base direction is right-to-left.
Public Constructors
Bidi(String paragraph, int flags)
Create Bidi from the given paragraph of text and base direction.
Bidi(AttributedCharacterIterator paragraph)
Create Bidi from the given paragraph of text.
Bidi(char[] text, int textStart, byte[] embeddings, int embStart, int paragraphLength, int flags)
Create Bidi from the given text, embedding, and direction information.
Public Methods
boolean baseIsLeftToRight()
Return true if the base direction is left-to-right.
Bidi createLineBidi(int lineStart, int lineLimit)
Create a Bidi object representing the bidi information on a line of text within the paragraph represented by the current Bidi.
int getBaseLevel()
Return the base level (0 if left-to-right, 1 if right-to-left).
int getLength()
Return the length of text in the line.
int getLevelAt(int offset)
Return the resolved level of the character at offset.
int getRunCount()
Return the number of level runs.
int getRunLevel(int run)
Return the level of the nth logical run in this line.
int getRunLimit(int run)
Return the index of the character past the end of the nth logical run in this line, as an offset from the start of the line.
int getRunStart(int run)
Return the index of the character at the start of the nth logical run in this line, as an offset from the start of the line.
boolean isLeftToRight()
Return true if the line is all left-to-right text and the base direction is left-to-right.
boolean isMixed()
Return true if the line is not left-to-right or right-to-left.
boolean isRightToLeft()
Return true if the line is all right-to-left text, and the base direction is right-to-left.
static void reorderVisually(byte[] levels, int levelStart, Object[] objects, int objectStart, int count)
Reorder the objects in the array into visual order based on their levels.
static boolean requiresBidi(char[] text, int start, int limit)
Return true if the specified text requires bidi analysis.
String toString()
Display the bidi internal state, used in debugging.
[Expand]
Inherited Methods
From class java.lang.Object

Constants

public static final int DIRECTION_DEFAULT_LEFT_TO_RIGHT

Constant indicating that the base direction depends on the first strong directional character in the text according to the Unicode Bidirectional Algorithm. If no strong directional character is present, the base direction is left-to-right.

Constant Value: -2 (0xfffffffe)

public static final int DIRECTION_DEFAULT_RIGHT_TO_LEFT

Constant indicating that the base direction depends on the first strong directional character in the text according to the Unicode Bidirectional Algorithm. If no strong directional character is present, the base direction is right-to-left.

Constant Value: -1 (0xffffffff)

public static final int DIRECTION_LEFT_TO_RIGHT

Constant indicating base direction is left-to-right.

Constant Value: 0 (0x00000000)

public static final int DIRECTION_RIGHT_TO_LEFT

Constant indicating base direction is right-to-left.

Constant Value: 1 (0x00000001)

Public Constructors

public Bidi (String paragraph, int flags)

Create Bidi from the given paragraph of text and base direction.

Parameters
paragraph a paragraph of text
flags a collection of flags that control the algorithm. The algorithm understands the flags DIRECTION_LEFT_TO_RIGHT, DIRECTION_RIGHT_TO_LEFT, DIRECTION_DEFAULT_LEFT_TO_RIGHT, and DIRECTION_DEFAULT_RIGHT_TO_LEFT. Other values are reserved.

public Bidi (AttributedCharacterIterator paragraph)

Create Bidi from the given paragraph of text.

The RUN_DIRECTION attribute in the text, if present, determines the base direction (left-to-right or right-to-left). If not present, the base direction is computes using the Unicode Bidirectional Algorithm, defaulting to left-to-right if there are no strong directional characters in the text. This attribute, if present, must be applied to all the text in the paragraph.

The BIDI_EMBEDDING attribute in the text, if present, represents embedding level information. Negative values from -1 to -62 indicate overrides at the absolute value of the level. Positive values from 1 to 62 indicate embeddings. Where values are zero or not defined, the base embedding level as determined by the base direction is assumed.

The NUMERIC_SHAPING attribute in the text, if present, converts European digits to other decimal digits before running the bidi algorithm. This attribute, if present, must be applied to all the text in the paragraph.

Parameters
paragraph a paragraph of text with optional character and paragraph attribute information
See Also

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

Create Bidi from the given text, embedding, and direction information. The embeddings array may be null. If present, the values represent embedding level information. Negative values from -1 to -61 indicate overrides at the absolute value of the level. Positive values from 1 to 61 indicate embeddings. Where values are zero, the base embedding level as determined by the base direction is assumed.

Parameters
text an array containing the paragraph of text to process.
textStart the index into the text array of the start of the paragraph.
embeddings an array containing embedding values for each character in the paragraph. This can be null, in which case it is assumed that there is no external embedding information.
embStart the index into the embedding array of the start of the paragraph.
paragraphLength the length of the paragraph in the text and embeddings arrays.
flags a collection of flags that control the algorithm. The algorithm understands the flags DIRECTION_LEFT_TO_RIGHT, DIRECTION_RIGHT_TO_LEFT, DIRECTION_DEFAULT_LEFT_TO_RIGHT, and DIRECTION_DEFAULT_RIGHT_TO_LEFT. Other values are reserved.

Public Methods

public boolean baseIsLeftToRight ()

Return true if the base direction is left-to-right.

Returns
  • true if the base direction is left-to-right

public Bidi createLineBidi (int lineStart, int lineLimit)

Create a Bidi object representing the bidi information on a line of text within the paragraph represented by the current Bidi. This call is not required if the entire paragraph fits on one line.

Parameters
lineStart the offset from the start of the paragraph to the start of the line.
lineLimit the offset from the start of the paragraph to the limit of the line.

public int getBaseLevel ()

Return the base level (0 if left-to-right, 1 if right-to-left).

Returns
  • the base level

public int getLength ()

Return the length of text in the line.

Returns
  • the length of text in the line

public int getLevelAt (int offset)

Return the resolved level of the character at offset. If offset is <0 or >= the length of the line, return the base direction level.

Parameters
offset the index of the character for which to return the level
Returns
  • the resolved level of the character at offset

public int getRunCount ()

Return the number of level runs.

Returns
  • the number of level runs

public int getRunLevel (int run)

Return the level of the nth logical run in this line.

Parameters
run the index of the run, between 0 and getRunCount()
Returns
  • the level of the run

public int getRunLimit (int run)

Return the index of the character past the end of the nth logical run in this line, as an offset from the start of the line. For example, this will return the length of the line for the last run on the line.

Parameters
run the index of the run, between 0 and getRunCount()
Returns
  • limit the limit of the run

public int getRunStart (int run)

Return the index of the character at the start of the nth logical run in this line, as an offset from the start of the line.

Parameters
run the index of the run, between 0 and getRunCount()
Returns
  • the start of the run

public boolean isLeftToRight ()

Return true if the line is all left-to-right text and the base direction is left-to-right.

Returns
  • true if the line is all left-to-right text and the base direction is left-to-right

public boolean isMixed ()

Return true if the line is not left-to-right or right-to-left. This means it either has mixed runs of left-to-right and right-to-left text, or the base direction differs from the direction of the only run of text.

Returns
  • true if the line is not left-to-right or right-to-left.

public boolean isRightToLeft ()

Return true if the line is all right-to-left text, and the base direction is right-to-left.

Returns
  • true if the line is all right-to-left text, and the base direction is right-to-left

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

Reorder the objects in the array into visual order based on their levels. This is a utility function to use when you have a collection of objects representing runs of text in logical order, each run containing text at a single level. The elements at index from objectStart up to objectStart + count in the objects array will be reordered into visual order assuming each run of text has the level indicated by the corresponding element in the levels array (at index - objectStart + levelStart).

Parameters
levels an array representing the bidi level of each object
levelStart the start position in the levels array
objects the array of objects to be reordered into visual order
objectStart the start position in the objects array
count the number of objects to reorder

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

Return true if the specified text requires bidi analysis. If this returns false, the text will display left-to-right. Clients can then avoid constructing a Bidi object. Text in the Arabic Presentation Forms area of Unicode is presumed to already be shaped and ordered for display, and so will not cause this function to return true.

Parameters
text the text containing the characters to test
start the start of the range of characters to test
limit the limit of the range of characters to test
Returns
  • true if the range of characters requires bidi analysis

public String toString ()

Display the bidi internal state, used in debugging.

Returns
  • a string representation of the object.