CharSequence

  • The CharSequence interface provides read-only access to a sequence of char values, representing characters in the Basic Multilingual Plane (BMP) or surrogates.

  • Common implementations include String, StringBuffer, StringBuilder, and CharBuffer.

  • Key methods allow retrieving individual characters (charAt), subsequences (subSequence), the sequence length (length), and converting the sequence to a String (toString).

  • CharSequence also offers methods (chars, codePoints) to create streams of int values representing the characters or code points within the sequence.

  • Comparing two CharSequence objects using equals or hashCode generally yields undefined results due to potential implementation differences.
public interface CharSequence
Known Indirect Subclasses

A CharSequence is a readable sequence of char values. This interface provides uniform, read-only access to many different kinds of char sequences. A char value represents a character in the Basic Multilingual Plane (BMP) or a surrogate. Refer to Unicode Character Representation for details.

This interface does not refine the general contracts of the equals and hashCode methods. The result of comparing two objects that implement CharSequence is therefore, in general, undefined. Each object may be implemented by a different class, and there is no guarantee that each class will be capable of testing its instances for equality with those of the other. It is therefore inappropriate to use arbitrary CharSequence instances as elements in a set or as keys in a map.

Public Method Summary

abstract char
charAt(int index)
Returns the char value at the specified index.
IntStream
chars()
Returns a stream of int zero-extending the char values from this sequence.
IntStream
codePoints()
Returns a stream of code point values from this sequence.
abstract int
length()
Returns the length of this character sequence.
abstract CharSequence
subSequence(int start, int end)
Returns a CharSequence that is a subsequence of this sequence.
abstract String
toString()
Returns a string containing the characters in this sequence in the same order as this sequence.

Public Methods

public abstract char charAt (int index)

Returns the char value at the specified index. An index ranges from zero to length() - 1. The first char value of the sequence is at index zero, the next at index one, and so on, as for array indexing.

If the char value specified by the index is a surrogate, the surrogate value is returned.

Parameters
index the index of the char value to be returned
Returns
  • the specified char value
Throws
IndexOutOfBoundsException if the index argument is negative or not less than length()

public IntStream chars ()

Returns a stream of int zero-extending the char values from this sequence. Any char which maps to a surrogate code point is passed through uninterpreted.

If the sequence is mutated while the stream is being read, the result is undefined.

Returns
  • an IntStream of char values from this sequence

public IntStream codePoints ()

Returns a stream of code point values from this sequence. Any surrogate pairs encountered in the sequence are combined as if by {@linkplain Character#toCodePoint Character.toCodePoint} and the result is passed to the stream. Any other code units, including ordinary BMP characters, unpaired surrogates, and undefined code units, are zero-extended to int values which are then passed to the stream.

If the sequence is mutated while the stream is being read, the result is undefined.

Returns
  • an IntStream of Unicode code points from this sequence

public abstract int length ()

Returns the length of this character sequence. The length is the number of 16-bit chars in the sequence.

Returns
  • the number of chars in this sequence

public abstract CharSequence subSequence (int start, int end)

Returns a CharSequence that is a subsequence of this sequence. The subsequence starts with the char value at the specified index and ends with the char value at index end - 1. The length (in chars) of the returned sequence is end - start, so if start == end then an empty sequence is returned.

Parameters
start the start index, inclusive
end the end index, exclusive
Returns
  • the specified subsequence
Throws
IndexOutOfBoundsException if start or end are negative, if end is greater than length(), or if start is greater than end

public abstract String toString ()

Returns a string containing the characters in this sequence in the same order as this sequence. The length of the string will be the length of this sequence.

Returns
  • a string consisting of exactly this sequence of characters