Module java.base
Package java.nio

Class CharBuffer

java.lang.Object
java.nio.Buffer
java.nio.CharBuffer
All Implemented Interfaces:
Appendable, CharSequence, Comparable<CharBuffer>, Readable
public abstract sealed class CharBuffer extends Buffer implements Comparable<CharBuffer>, Appendable, CharSequence, Readable
A char buffer.

This class defines four categories of operations upon char buffers:

  • Absolute and relative get and put methods that read and write single chars;

  • Absolute and relative bulk get methods that transfer contiguous sequences of chars from this buffer into an array;

  • Absolute and relative bulk put methods that transfer contiguous sequences of chars from a char array, a string, or some other char buffer into this buffer;

  • A method for compacting a char buffer.

Char buffers can be created either by allocation, which allocates space for the buffer's content, by wrapping an existing char array or string into a buffer, or by creating a view of an existing byte buffer.

Like a byte buffer, a char buffer is either direct or non-direct. A char buffer created via the wrap methods of this class will be non-direct. A char buffer created as a view of a byte buffer will be direct if, and only if, the byte buffer itself is direct. Whether or not a char buffer is direct may be determined by invoking the isDirect method.

This class implements the CharSequence interface so that character buffers may be used wherever character sequences are accepted, for example in the regular-expression package java.util.regex. The methods defined by CharSequence operate relative to the current position of the buffer when they are invoked.

Methods in this class that do not otherwise have a value to return are specified to return the buffer upon which they are invoked. This allows method invocations to be chained. The sequence of statements 

    cb.put("text/");
    cb.put(subtype);
    cb.put("; charset=");
    cb.put(enc);
can, for example, be replaced by the single statement 
    cb.put("text/").put(subtype).put("; charset=").put(enc);

Optional operations

Methods specified as optional operations throw a ReadOnlyBufferException when invoked on a read-only CharBuffer. The methods array and arrayOffset throw an UnsupportedOperationException if the CharBuffer is not backed by an accessible char array (irrespective of whether the CharBuffer is read-only).
Since:
1.4

  • Method Summary

    Modifier and Type
    Method
    Description
    static CharBuffer
    allocate(int capacity)
    Allocates a new char buffer.
    CharBuffer
    append(char c)
    Appends the specified char to this buffer  (optional operation).
    CharBuffer
    append(CharSequence csq)
    Appends the specified character sequence to this buffer  (optional operation).
    CharBuffer
    append(CharSequence csq, int start, int end)
    Appends a subsequence of the specified character sequence to this buffer  (optional operation).
    final char[]
    array()
    Returns the char array that backs this buffer  (optional operation).
    final int
    arrayOffset()
    Returns the offset within this buffer's backing array of the first element of the buffer  (optional operation).
    abstract CharBuffer
    asReadOnlyBuffer()
    Creates a new, read-only char buffer that shares this buffer's content.
    final char
    charAt(int index)
    Reads the character at the given index relative to the current position.
    final CharBuffer
    clear()
    Clears this buffer.
    abstract CharBuffer
    compact()
    Compacts this buffer  (optional operation).
    int
    compareTo(CharBuffer that)
    Compares this buffer to another.
    abstract CharBuffer
    duplicate()
    Creates a new char buffer that shares this buffer's content.
    boolean
    equals(Object ob)
    Tells whether or not this buffer is equal to another object.
    final CharBuffer
    flip()
    Flips this buffer.
    abstract char
    get()
    Relative get method.
    CharBuffer
    get(char[] dst)
    Relative bulk get method.
    CharBuffer
    get(char[] dst, int offset, int length)
    Relative bulk get method.
    abstract char
    get(int index)
    Absolute get method.
    CharBuffer
    get(int index, char[] dst)
    Absolute bulk get method.
    CharBuffer
    get(int index, char[] dst, int offset, int length)
    Absolute bulk get method.
    final boolean
    hasArray()
    Tells whether or not this buffer is backed by an accessible char array.
    int
    hashCode()
    Returns the current hash code of this buffer.
    abstract boolean
    isDirect()
    Tells whether or not this char buffer is direct.
    final boolean
    isEmpty()
    Returns true if this character buffer is empty.
    final int
    length()
    Returns the length of this character buffer.
    final CharBuffer
    limit(int newLimit)
    Sets this buffer's limit.
    final CharBuffer
    mark()
    Sets this buffer's mark at its position.
    int
    mismatch(CharBuffer that)
    Finds and returns the relative index of the first mismatch between this buffer and a given buffer.
    abstract ByteOrder
    order()
    Retrieves this buffer's byte order.
    final CharBuffer
    position(int newPosition)
    Sets this buffer's position.
    abstract CharBuffer
    put(char c)
    Relative put method  (optional operation).
    final CharBuffer
    put(char[] src)
    Relative bulk put method  (optional operation).
    CharBuffer
    put(char[] src, int offset, int length)
    Relative bulk put method  (optional operation).
    abstract CharBuffer
    put(int index, char c)
    Absolute put method  (optional operation).
    CharBuffer
    put(int index, char[] src)
    Absolute bulk put method  (optional operation).
    CharBuffer
    put(int index, char[] src, int offset, int length)
    Absolute bulk put method  (optional operation).
    CharBuffer
    put(int index, CharBuffer src, int offset, int length)
    Absolute bulk put method  (optional operation).
    final CharBuffer
    put(String src)
    Relative bulk put method  (optional operation).
    CharBuffer
    put(String src, int start, int end)
    Relative bulk put method  (optional operation).
    CharBuffer
    put(CharBuffer src)
    Relative bulk put method  (optional operation).
    int
    read(CharBuffer target)
    Attempts to read characters into the specified character buffer.
    final CharBuffer
    reset()
    Resets this buffer's position to the previously-marked position.
    final CharBuffer
    rewind()
    Rewinds this buffer.
    abstract CharBuffer
    slice()
    Creates a new char buffer whose content is a shared subsequence of this buffer's content.
    abstract CharBuffer
    slice(int index, int length)
    Creates a new char buffer whose content is a shared subsequence of this buffer's content.
    abstract CharBuffer
    subSequence(int start, int end)
    Creates a new character buffer that represents the specified subsequence of this buffer, relative to the current position.
    String
    toString()
    Returns a string containing the characters in this buffer.
    static CharBuffer
    wrap(char[] array)
    Wraps a char array into a buffer.
    static CharBuffer
    wrap(char[] array, int offset, int length)
    Wraps a char array into a buffer.
    static CharBuffer
    wrap(CharSequence csq)
    Wraps a character sequence into a buffer.
    static CharBuffer
    wrap(CharSequence csq, int start, int end)
    Wraps a character sequence into a buffer.

    Methods declared in class java.nio.Buffer

    capacity, hasRemaining, isReadOnly, limit, position, remaining

    Methods declared in class java.lang.Object

    clone, finalize, getClass, notify, notifyAll, wait, wait, wait

    Methods declared in interface java.lang.CharSequence

    chars, codePoints

  • Method Details

    • allocate

      public static CharBuffer allocate(int capacity)
      Allocates a new char buffer.

      The new buffer's position will be zero, its limit will be its capacity, its mark will be undefined, each of its elements will be initialized to zero, and its byte order will be the native order of the underlying hardware. It will have a backing array, and its array offset will be zero.

      Parameters:
      capacity - The new buffer's capacity, in chars
      Returns:
      The new char buffer
      Throws:
      IllegalArgumentException - If the capacity is a negative integer

    • wrap

      public static CharBuffer wrap(char[] array, int offset, int length)
      Wraps a char array into a buffer.

      The new buffer will be backed by the given char array; that is, modifications to the buffer will cause the array to be modified and vice versa. The new buffer's capacity will be array.length, its position will be offset, its limit will be offset + length, its mark will be undefined, and its byte order will be the native order of the underlying hardware. Its backing array will be the given array, and its array offset will be zero.

      Parameters:
      array - The array that will back the new buffer
      offset - The offset of the subarray to be used; must be non-negative and no larger than array.length. The new buffer's position will be set to this value.
      length - The length of the subarray to be used; must be non-negative and no larger than array.length - offset. The new buffer's limit will be set to offset + length.
      Returns:
      The new char buffer
      Throws:
      IndexOutOfBoundsException - If the preconditions on the offset and length parameters do not hold

    • wrap

      public static CharBuffer wrap(char[] array)
      Wraps a char array into a buffer.

      The new buffer will be backed by the given char array; that is, modifications to the buffer will cause the array to be modified and vice versa. The new buffer's capacity and limit will be array.length, its position will be zero, its mark will be undefined, and its byte order will be the native order of the underlying hardware. Its backing array will be the given array, and its array offset will be zero.

      Parameters:
      array - The array that will back this buffer
      Returns:
      The new char buffer

    • read

      public int read(CharBuffer target) throws IOException
      Attempts to read characters into the specified character buffer. The buffer is used as a repository of characters as-is: the only changes made are the results of a put operation. No flipping or rewinding of the buffer is performed.
      Specified by:
      read in interface Readable
      Parameters:
      target - the buffer to read characters into
      Returns:
      The number of characters added to the buffer, or -1 if this source of characters is at its end
      Throws:
      IOException - if an I/O error occurs
      ReadOnlyBufferException - if target is a read only buffer
      Since:
      1.5

    • wrap

      public static CharBuffer wrap(CharSequence csq, int start, int end)
      Wraps a character sequence into a buffer.

      The content of the new, read-only buffer will be the content of the given character sequence. The buffer's capacity will be csq.length(), its position will be start, its limit will be end, and its mark will be undefined.

      Parameters:
      csq - The character sequence from which the new character buffer is to be created
      start - The index of the first character to be used; must be non-negative and no larger than csq.length(). The new buffer's position will be set to this value.
      end - The index of the character following the last character to be used; must be no smaller than start and no larger than csq.length(). The new buffer's limit will be set to this value.
      Returns:
      The new character buffer
      Throws:
      IndexOutOfBoundsException - If the preconditions on the start and end parameters do not hold

    • wrap

      public static CharBuffer wrap(CharSequence csq)
      Wraps a character sequence into a buffer.

      The content of the new, read-only buffer will be the content of the given character sequence. The new buffer's capacity and limit will be csq.length(), its position will be zero, and its mark will be undefined.

      Parameters:
      csq - The character sequence from which the new character buffer is to be created
      Returns:
      The new character buffer

    • slice

      public abstract CharBuffer slice()
      Creates a new char buffer whose content is a shared subsequence of this buffer's content.

      The content of the new buffer will start at this buffer's current position. Changes to this buffer's content will be visible in the new buffer, and vice versa; the two buffers' position, limit, and mark values will be independent.

      The new buffer's position will be zero, its capacity and its limit will be the number of chars remaining in this buffer, its mark will be undefined, and its byte order will be identical to that of this buffer. The new buffer will be direct if, and only if, this buffer is direct, and it will be read-only if, and only if, this buffer is read-only.

      Specified by:
      slice in class Buffer
      Returns:
      The new char buffer

    • slice

      public abstract CharBuffer slice(int index, int length)
      Creates a new char buffer whose content is a shared subsequence of this buffer's content.

      The content of the new buffer will start at position index in this buffer, and will contain length elements. Changes to this buffer's content will be visible in the new buffer, and vice versa; the two buffers' position, limit, and mark values will be independent.

      The new buffer's position will be zero, its capacity and its limit will be length, its mark will be undefined, and its byte order will be identical to that of this buffer. The new buffer will be direct if, and only if, this buffer is direct, and it will be read-only if, and only if, this buffer is read-only.

      Specified by:
      slice in class Buffer
      Parameters:
      index - The position in this buffer at which the content of the new buffer will start; must be non-negative and no larger than limit()
      length - The number of elements the new buffer will contain; must be non-negative and no larger than limit() - index
      Returns:
      The new buffer
      Throws:
      IndexOutOfBoundsException - If index is negative or greater than limit(), length is negative, or length > limit() - index
      Since:
      13

    • duplicate

      public abstract CharBuffer duplicate()
      Creates a new char buffer that shares this buffer's content.

      The content of the new buffer will be that of this buffer. Changes to this buffer's content will be visible in the new buffer, and vice versa; the two buffers' position, limit, and mark values will be independent.

      The new buffer's capacity, limit, position, mark values, and byte order will be identical to those of this buffer. The new buffer will be direct if, and only if, this buffer is direct, and it will be read-only if, and only if, this buffer is read-only.

      Specified by:
      duplicate in class Buffer
      Returns:
      The new char buffer

    • asReadOnlyBuffer

      public abstract CharBuffer asReadOnlyBuffer()
      Creates a new, read-only char buffer that shares this buffer's content.

      The content of the new buffer will be that of this buffer. Changes to this buffer's content will be visible in the new buffer; the new buffer itself, however, will be read-only and will not allow the shared content to be modified. The two buffers' position, limit, and mark values will be independent.

      The new buffer's capacity, limit, position, mark values, and byte order will be identical to those of this buffer.

      If this buffer is itself read-only then this method behaves in exactly the same way as the duplicate method.

      Returns:
      The new, read-only char buffer

    • get

      public abstract char get()
      Relative get method. Reads the char at this buffer's current position, and then increments the position.
      Returns:
      The char at the buffer's current position
      Throws:
      BufferUnderflowException - If the buffer's current position is not smaller than its limit

    • put

      public abstract CharBuffer put(char c)
      Relative put method  (optional operation).

      Writes the given char into this buffer at the current position, and then increments the position.

      Parameters:
      c - The char to be written
      Returns:
      This buffer
      Throws:
      BufferOverflowException - If this buffer's current position is not smaller than its limit
      ReadOnlyBufferException - If this buffer is read-only

    • get

      public abstract char get(int index)
      Absolute get method. Reads the char at the given index.
      Parameters:
      index - The index from which the char will be read
      Returns:
      The char at the given index
      Throws:
      IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit

    • put

      public abstract CharBuffer put(int index, char c)
      Absolute put method  (optional operation).

      Writes the given char into this buffer at the given index.

      Parameters:
      index - The index at which the char will be written
      c - The char value to be written
      Returns:
      This buffer
      Throws:
      IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit
      ReadOnlyBufferException - If this buffer is read-only

    • get

      public CharBuffer get(char[] dst, int offset, int length)
      Relative bulk get method.

      This method transfers chars from this buffer into the given destination array. If there are fewer chars remaining in the buffer than are required to satisfy the request, that is, if length > remaining(), then no chars are transferred and a BufferUnderflowException is thrown.

      Otherwise, this method copies length chars from this buffer into the given array, starting at the current position of this buffer and at the given offset in the array. The position of this buffer is then incremented by length.

      In other words, an invocation of this method of the form src.get(dst, off, len) has exactly the same effect as the loop 

          for (int i = off; i < off + len; i++)
        dst[i] = src.get();
      except that it first checks that there are sufficient chars in this buffer and it is potentially much more efficient.

      Parameters:
      dst - The array into which chars are to be written
      offset - The offset within the array of the first char to be written; must be non-negative and no larger than dst.length
      length - The maximum number of chars to be written to the given array; must be non-negative and no larger than dst.length - offset
      Returns:
      This buffer
      Throws:
      BufferUnderflowException - If there are fewer than length chars remaining in this buffer
      IndexOutOfBoundsException - If the preconditions on the offset and length parameters do not hold

    • get

      public CharBuffer get(char[] dst)
      Relative bulk get method.

      This method transfers chars from this buffer into the given destination array. An invocation of this method of the form src.get(a) behaves in exactly the same way as the invocation 

          src.get(a, 0, a.length)

      Parameters:
      dst - The destination array
      Returns:
      This buffer
      Throws:
      BufferUnderflowException - If there are fewer than length chars remaining in this buffer

    • get

      public CharBuffer get(int index, char[] dst, int offset, int length)
      Absolute bulk get method.

      This method transfers length chars from this buffer into the given array, starting at the given index in this buffer and at the given offset in the array. The position of this buffer is unchanged.

      An invocation of this method of the form src.get(index, dst, offset, length) has exactly the same effect as the following loop except that it first checks the consistency of the supplied parameters and it is potentially much more efficient: 

          for (int i = offset, j = index; i < offset + length; i++, j++)
        dst[i] = src.get(j);

      Parameters:
      index - The index in this buffer from which the first char will be read; must be non-negative and less than limit()
      dst - The destination array
      offset - The offset within the array of the first char to be written; must be non-negative and less than dst.length
      length - The number of chars to be written to the given array; must be non-negative and no larger than the smaller of limit() - index and dst.length - offset
      Returns:
      This buffer
      Throws:
      IndexOutOfBoundsException - If the preconditions on the index, offset, and length parameters do not hold
      Since:
      13

    • get

      public CharBuffer get(int index, char[] dst)
      Absolute bulk get method.

      This method transfers chars from this buffer into the given destination array. The position of this buffer is unchanged. An invocation of this method of the form src.get(index, dst) behaves in exactly the same way as the invocation: 

          src.get(index, dst, 0, dst.length)

      Parameters:
      index - The index in this buffer from which the first char will be read; must be non-negative and less than limit()
      dst - The destination array
      Returns:
      This buffer
      Throws:
      IndexOutOfBoundsException - If index is negative, not smaller than limit(), or limit() - index < dst.length
      Since:
      13

    • put

      public CharBuffer put(CharBuffer src)
      Relative bulk put method  (optional operation).

      This method transfers the chars remaining in the given source buffer into this buffer. If there are more chars remaining in the source buffer than in this buffer, that is, if src.remaining() > remaining(), then no chars are transferred and a BufferOverflowException is thrown.

      Otherwise, this method copies n = src.remaining() chars from the given buffer into this buffer, starting at each buffer's current position. The positions of both buffers are then incremented by n.

      In other words, an invocation of this method of the form dst.put(src) has exactly the same effect as the loop 

          while (src.hasRemaining())
        dst.put(src.get());
      except that it first checks that there is sufficient space in this buffer and it is potentially much more efficient. If this buffer and the source buffer share the same backing array or memory, then the result will be as if the source elements were first copied to an intermediate location before being written into this buffer.

      Parameters:
      src - The source buffer from which chars are to be read; must not be this buffer
      Returns:
      This buffer
      Throws:
      BufferOverflowException - If there is insufficient space in this buffer for the remaining chars in the source buffer
      IllegalArgumentException - If the source buffer is this buffer
      ReadOnlyBufferException - If this buffer is read-only

    • put

      public CharBuffer put(int index, CharBuffer src, int offset, int length)
      Absolute bulk put method  (optional operation).

      This method transfers length chars into this buffer from the given source buffer, starting at the given offset in the source buffer and the given index in this buffer. The positions of both buffers are unchanged.

      In other words, an invocation of this method of the form dst.put(index, src, offset, length) has exactly the same effect as the loop 

          for (int i = offset, j = index; i < offset + length; i++, j++)
        dst.put(j, src.get(i));
      except that it first checks the consistency of the supplied parameters and it is potentially much more efficient. If this buffer and the source buffer share the same backing array or memory, then the result will be as if the source elements were first copied to an intermediate location before being written into this buffer.

      Parameters:
      index - The index in this buffer at which the first char will be written; must be non-negative and less than limit()
      src - The buffer from which chars are to be read
      offset - The index within the source buffer of the first char to be read; must be non-negative and less than src.limit()
      length - The number of chars to be read from the given buffer; must be non-negative and no larger than the smaller of limit() - index and src.limit() - offset
      Returns:
      This buffer
      Throws:
      IndexOutOfBoundsException - If the preconditions on the index, offset, and length parameters do not hold
      ReadOnlyBufferException - If this buffer is read-only
      Since:
      16

    • put

      public CharBuffer put(char[] src, int offset, int length)
      Relative bulk put method  (optional operation).

      This method transfers chars into this buffer from the given source array. If there are more chars to be copied from the array than remain in this buffer, that is, if length > remaining(), then no chars are transferred and a BufferOverflowException is thrown.

      Otherwise, this method copies length chars from the given array into this buffer, starting at the given offset in the array and at the current position of this buffer. The position of this buffer is then incremented by length.

      In other words, an invocation of this method of the form dst.put(src, off, len) has exactly the same effect as the loop 

          for (int i = off; i < off + len; i++)
        dst.put(src[i]);
      except that it first checks that there is sufficient space in this buffer and it is potentially much more efficient.

      Parameters:
      src - The array from which chars are to be read
      offset - The offset within the array of the first char to be read; must be non-negative and no larger than src.length
      length - The number of chars to be read from the given array; must be non-negative and no larger than src.length - offset
      Returns:
      This buffer
      Throws:
      BufferOverflowException - If there is insufficient space in this buffer
      IndexOutOfBoundsException - If the preconditions on the offset and length parameters do not hold
      ReadOnlyBufferException - If this buffer is read-only

    • put

      public final CharBuffer put(char[] src)
      Relative bulk put method  (optional operation).

      This method transfers the entire content of the given source char array into this buffer. An invocation of this method of the form dst.put(a) behaves in exactly the same way as the invocation 

          dst.put(a, 0, a.length)

      Parameters:
      src - The source array
      Returns:
      This buffer
      Throws:
      BufferOverflowException - If there is insufficient space in this buffer
      ReadOnlyBufferException - If this buffer is read-only

    • put

      public CharBuffer put(int index, char[] src, int offset, int length)
      Absolute bulk put method  (optional operation).

      This method transfers length chars from the given array, starting at the given offset in the array and at the given index in this buffer. The position of this buffer is unchanged.

      An invocation of this method of the form dst.put(index, src, offset, length) has exactly the same effect as the following loop except that it first checks the consistency of the supplied parameters and it is potentially much more efficient: 

          for (int i = offset, j = index; i < offset + length; i++, j++)
        dst.put(j, src[i]);

      Parameters:
      index - The index in this buffer at which the first char will be written; must be non-negative and less than limit()
      src - The array from which chars are to be read
      offset - The offset within the array of the first char to be read; must be non-negative and less than src.length
      length - The number of chars to be read from the given array; must be non-negative and no larger than the smaller of limit() - index and src.length - offset
      Returns:
      This buffer
      Throws:
      IndexOutOfBoundsException - If the preconditions on the index, offset, and length parameters do not hold
      ReadOnlyBufferException - If this buffer is read-only
      Since:
      13

    • put

      public CharBuffer put(int index, char[] src)
      Absolute bulk put method  (optional operation).

      This method copies chars into this buffer from the given source array. The position of this buffer is unchanged. An invocation of this method of the form dst.put(index, src) behaves in exactly the same way as the invocation: 

          dst.put(index, src, 0, src.length);

      Parameters:
      index - The index in this buffer at which the first char will be written; must be non-negative and less than limit()
      src - The array from which chars are to be read
      Returns:
      This buffer
      Throws:
      IndexOutOfBoundsException - If index is negative, not smaller than limit(), or limit() - index < src.length
      ReadOnlyBufferException - If this buffer is read-only
      Since:
      13

    • put

      public CharBuffer put(String src, int start, int end)
      Relative bulk put method  (optional operation).

      This method transfers chars from the given string into this buffer. If there are more chars to be copied from the string than remain in this buffer, that is, if end - start > remaining(), then no chars are transferred and a BufferOverflowException is thrown.

      Otherwise, this method copies n = end - start chars from the given string into this buffer, starting at the given start index and at the current position of this buffer. The position of this buffer is then incremented by n.

      In other words, an invocation of this method of the form dst.put(src, start, end) has exactly the same effect as the loop 

          for (int i = start; i < end; i++)
        dst.put(src.charAt(i));
      except that it first checks that there is sufficient space in this buffer and it is potentially much more efficient.

      Parameters:
      src - The string from which chars are to be read
      start - The offset within the string of the first char to be read; must be non-negative and no larger than string.length()
      end - The offset within the string of the last char to be read, plus one; must be non-negative and no larger than string.length()
      Returns:
      This buffer
      Throws: