Replaceable

public interface Replaceable

Replaceable is an interface representing a string of characters that supports the replacement of a range of itself with a new string of characters. It is used by APIs that change a piece of text while retaining metadata. Metadata is data other than the Unicode characters returned by char32At(). One example of metadata is style attributes; another is an edit history, marking each character with an author and revision number.

An implicit aspect of the Replaceable API is that during a replace operation, new characters take on the metadata of the old characters. For example, if the string "the bold font" has range (4, 8) replaced with "strong", then it becomes "the strong font".

Replaceable specifies ranges using a start offset and a limit offset. The range of characters thus specified includes the characters at offset start..limit-1. That is, the start offset is inclusive, and the limit offset is exclusive.

Replaceable also includes API to access characters in the string: length(), charAt(), char32At(), and extractBetween().

For a subclass to support metadata, typical behavior of replace() is the following:

  • Set the metadata of the new text to the metadata of the first character replaced
  • If no characters are replaced, use the metadata of the previous character
  • If there is no previous character (i.e. start == 0), use the following character
  • If there is no following character (i.e. the replaceable was empty), use default metadata
  • If the code point U+FFFF is seen, it should be interpreted as a special marker having no metadata
If this is not the behavior, the subclass should document any differences.

Copyright © IBM Corporation 1999. All rights reserved.

Public Method Summary

abstract int
char32At(int offset)
Returns the 32-bit code point at the given 16-bit offset into the text.
abstract char
charAt(int offset)
Returns the 16-bit code unit at the given offset into the text.
abstract void
copy(int start, int limit, int dest)
Copies a substring of this object, retaining metadata.
abstract void
getChars(int srcStart, int srcLimit, char[] dst, int dstStart)
Copies characters from this object into the destination character array.
abstract boolean
hasMetaData()
R Returns true if this object contains metadata.
abstract int
length()
Returns the number of 16-bit code units in the text.
abstract void
replace(int start, int limit, char[] chars, int charsStart, int charsLen)
Replaces a substring of this object with the given text.
abstract void
replace(int start, int limit, String text)
Replaces a substring of this object with the given text.

Public Methods

public abstract int char32At (int offset)

Returns the 32-bit code point at the given 16-bit offset into the text. This assumes the text is stored as 16-bit code units with surrogate pairs intermixed. If the offset of a leading or trailing code unit of a surrogate pair is given, return the code point of the surrogate pair.

Most subclasses can return android.icu.text.UTF16.charAt(this, offset).

Parameters
offset an integer between 0 and length()-1 inclusive
Returns
  • 32-bit code point of text at given offset

public abstract char charAt (int offset)

Returns the 16-bit code unit at the given offset into the text.

Parameters
offset an integer between 0 and length()-1 inclusive
Returns
  • 16-bit code unit of text at given offset

public abstract void copy (int start, int limit, int dest)

Copies a substring of this object, retaining metadata. This method is used to duplicate or reorder substrings. The destination index must not overlap the source range. If hasMetaData() returns false, subclasses may use the naive implementation:

 char[] text = new char[limit - start];
 getChars(start, limit, text, 0);
 replace(dest, dest, text, 0, limit - start);

Parameters
start the beginning index, inclusive; 0 <= start <= limit.
limit the ending index, exclusive; start <= limit <= length().
dest the destination index. The characters from start..limit-1 will be copied to dest. Implementations of this method may assume that dest <= start || dest >= limit.

public abstract void getChars (int srcStart, int srcLimit, char[] dst, int dstStart)

Copies characters from this object into the destination character array. The first character to be copied is at index srcStart; the last character to be copied is at index srcLimit-1 (thus the total number of characters to be copied is srcLimit-srcStart). The characters are copied into the subarray of dst starting at index dstStart and ending at index dstStart + (srcLimit-srcStart) - 1.

Parameters
srcStart the beginning index to copy, inclusive; 0 <= start <= limit.
srcLimit the ending index to copy, exclusive; start <= limit <= length().
dst the destination array.
dstStart the start offset in the destination array.

public abstract boolean hasMetaData ()

R Returns true if this object contains metadata. If a Replaceable object has metadata, calls to the Replaceable API must be made so as to preserve metadata. If it does not, calls to the Replaceable API may be optimized to improve performance.

Returns
  • true if this object contains metadata

public abstract int length ()

Returns the number of 16-bit code units in the text.

Returns
  • number of 16-bit code units in text

public abstract void replace (int start, int limit, char[] chars, int charsStart, int charsLen)

Replaces a substring of this object with the given text.

Subclasses must ensure that if the text between start and limit is equal to the replacement text, that replace has no effect. That is, any metadata should be unaffected. In addition, subclasses are encouraged to check for initial and trailing identical characters, and make a smaller replacement if possible. This will preserve as much metadata as possible.

Parameters
start the beginning index, inclusive; 0 <= start <= limit.
limit the ending index, exclusive; start <= limit <= length().
chars the text to replace characters start to limit - 1
charsStart the beginning index into chars, inclusive; 0 <= start <= limit.
charsLen the number of characters of chars.

public abstract void replace (int start, int limit, String text)

Replaces a substring of this object with the given text.

Subclasses must ensure that if the text between start and limit is equal to the replacement text, that replace has no effect. That is, any metadata should be unaffected. In addition, subclasses are encouraged to check for initial and trailing identical characters, and make a smaller replacement if possible. This will preserve as much metadata as possible.

Parameters
start the beginning index, inclusive; 0 <= start <= limit.
limit the ending index, exclusive; start <= limit <= length().
text the text to replace characters start to limit - 1