Module java.base
Package java.lang

Interface CharSequence

All Known Subinterfaces:
Name
All Known Implementing Classes:
CharBuffer, Segment, String, StringBuffer, StringBuilder

public interface CharSequence
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 testing two objects that implement CharSequence for equality 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.

Since:
1.4
  • Method Summary

    Modifier and Type Method Description
    char charAt​(int index)
    Returns the char value at the specified index.
    default IntStream chars()
    Returns a stream of int zero-extending the char values from this sequence.
    default IntStream codePoints()
    Returns a stream of code point values from this sequence.
    static int compare​(CharSequence cs1, CharSequence cs2)
    Compares two CharSequence instances lexicographically.
    default boolean isEmpty()
    Returns true if this character sequence is empty.
    int length()
    Returns the length of this character sequence.
    CharSequence subSequence​(int start, int end)
    Returns a CharSequence that is a subsequence of this sequence.
    String toString()
    Returns a string containing the characters in this sequence in the same order as this sequence.
  • Method Details

    • length

      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
    • charAt

      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()
    • isEmpty

      default boolean isEmpty()
      Returns true if this character sequence is empty.
      Implementation Requirements:
      The default implementation returns the result of calling length() == 0.
      Returns:
      true if length() is 0, otherwise false
      Since:
      15
    • subSequence

      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
    • toString

      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.
      Overrides:
      toString in class Object
      Returns:
      a string consisting of exactly this sequence of characters
    • chars

      default 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.

      The stream binds to this sequence when the terminal stream operation commences (specifically, for mutable sequences the spliterator for the stream is late-binding). If the sequence is modified during that operation then the result is undefined.

      Returns:
      an IntStream of char values from this sequence
      Since:
      1.8
    • codePoints

      default IntStream codePoints()
      Returns a stream of code point values from this sequence. Any surrogate pairs encountered in the sequence are combined as if by 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.

      The stream binds to this sequence when the terminal stream operation commences (specifically, for mutable sequences the spliterator for the stream is late-binding). If the sequence is modified during that operation then the result is undefined.

      Returns:
      an IntStream of Unicode code points from this sequence
      Since:
      1.8
    • compare

      static int compare(CharSequence cs1, CharSequence cs2)
      Compares two CharSequence instances lexicographically. Returns a negative value, zero, or a positive value if the first sequence is lexicographically less than, equal to, or greater than the second, respectively.

      The lexicographical ordering of CharSequence is defined as follows. Consider a CharSequence cs of length len to be a sequence of char values, cs[0] to cs[len-1]. Suppose k is the lowest index at which the corresponding char values from each sequence differ. The lexicographic ordering of the sequences is determined by a numeric comparison of the char values cs1[k] with cs2[k]. If there is no such index k, the shorter sequence is considered lexicographically less than the other. If the sequences have the same length, the sequences are considered lexicographically equal.

      Parameters:
      cs1 - the first CharSequence
      cs2 - the second CharSequence
      Returns:
      the value 0 if the two CharSequence are equal; a negative integer if the first CharSequence is lexicographically less than the second; or a positive integer if the first CharSequence is lexicographically greater than the second.
      Since:
      11