Documentation  › java.nio  › CharBuffer
 
 


  CharBuffer
  public abstract

  Inherits From:   Buffer : Object
  Conforms To:   CharSequence
Comparable
  Declared In:   java.nio


Class Description
 
A character buffer.

This class defines four categories of operations upon character buffers:

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

  • Relative get methods that transfer contiguous sequences of characters from this buffer into an array; and

  • Relative put methods that transfer contiguous sequences of characters from a character array, a string, or some other character buffer into this buffer; and

  • Methods for compacting, duplicating, and slicing a character buffer.

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

Like a byte buffer, a character buffer is either direct or non-direct. A character buffer created via the wrap methods of this class will be non-direct. A character 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 character 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.

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);


Class Variables
 
None declared in this class.


Instance Variables
 
None declared in this class.


Constructors
 
None declared in this class.


Class Methods
 
allocate
public static CharBuffer allocate( int capacity )

Allocates a new character buffer.

The new buffer's position will be zero, its limit will be its capacity, and its mark will be undefined. It will have a array, and its offset will be zero.


wrap
public static CharBuffer wrap( char[] array )

Wraps a character array into a buffer.

The new buffer will be backed by the the given character 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, and its mark will be undefined. Its array will be the given array, and its offset will be zero.




wrap
public static CharBuffer wrap( char[] array, int offset, int length )

Wraps a character array into a buffer.

The new buffer will be backed by the the given character 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, and its mark will be undefined. Its array will be the given array, and its offset will be zero.




wrap
public static CharBuffer wrap( CharSequence csq )

Wraps a string into a buffer.

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




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.



Instance Methods
 
array
public final char[] array( )

Returns the character array that backs this buffer  (optional operation).

Modifications to this buffer's content will cause the returned array's content to be modified, and vice versa.

Invoke the hasArray method before invoking this method in order to ensure that this buffer has an accessible backing array.




arrayOffset
public final int arrayOffset( )

Returns the offset within this buffer's backing array of the first element of the buffer  (optional operation).

If this buffer is backed by an array then buffer position p corresponds to array index p + arrayOffset().

Invoke the hasArray method before invoking this method in order to ensure that this buffer has an accessible backing array.




asReadOnlyBuffer
public abstract CharBuffer asReadOnlyBuffer( )

Creates a new, read-only character 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, and mark values 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.




charAt
public final char charAt( int index )

Reads the character at the given index relative to the current position.




compact
public abstract CharBuffer compact( )

Compacts this buffer  (optional operation).

The characters between the buffer's current position and its limit, if any, are copied to the beginning of the buffer. That is, the character at index p = position() is copied to index zero, the character at index p + 1 is copied to index one, and so forth until the character at index limit() - 1 is copied to index n = limit() - 1 - p. The buffer's position is then set to n+1 and its limit is set to its capacity. The mark, if defined, is discarded.

The buffer's position is set to the number of characters copied, rather than to zero, so that an invocation of this method can be followed immediately by an invocation of another relative put method.




compareTo
public int compareTo( Object ob )

Compares this buffer to another object.

Two char buffers are compared by comparing their sequences of remaining elements lexicographically, without regard to the starting position of each sequence within its corresponding buffer.

A char buffer is not comparable to any other type of object.




duplicate
public abstract CharBuffer duplicate( )

Creates a new character 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, and mark values 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.




equals
public boolean equals( Object ob )

Tells whether or not this buffer is equal to another object.

Two char buffers are equal if, and only if,

  1. They have the same element type,

  2. They have the same number of remaining elements, and

  3. The two sequences of remaining elements, considered independently of their starting positions, are pointwise equal.

A char buffer is not equal to any other type of object.




get
public abstract char get( )

Relative get method. Reads the character at this buffer's current position, and then increments the position.




get
public CharBuffer get( char[] dst )

Relative bulk get method.

This method transfers characters 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)



get
public CharBuffer get( char[] dst, int offset, int length )

Relative bulk get method.

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

Otherwise, this method copies length characters 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 characters in this buffer and it is potentially much more efficient.




get
public abstract char get( int index )

Absolute get method. Reads the character at the given index.




hasArray
public final boolean hasArray( )

Tells whether or not this buffer is backed by an accessible character array.

If this method returns true then the array and arrayOffset methods may safely be invoked.




hashCode
public int hashCode( )

Returns the current hash code of this buffer.

The hash code of a char buffer depends only upon its remaining elements; that is, upon the elements from position() up to, and including, the element at limit() - 1.

Because buffer hash codes are content-dependent, it is inadvisable to use buffers as keys in hash maps or similar data structures unless it is known that their contents will not change.




isDirect
public abstract boolean isDirect( )

Tells whether or not this character buffer is direct.




length
public final int length( )

Returns the length of this character buffer.

When viewed as a character sequence, the length of a character buffer is simply the number of characters between the position (inclusive) and the limit (exclusive); that is, it is equivalent to remaining().




order
public abstract ByteOrder order( )

Retrieves this buffer's byte order.

The byte order of a character buffer created by allocation or by wrapping an existing char array is the order of the underlying hardware. The byte order of a character buffer created as a view of a byte buffer is that of the byte buffer at the moment that the view is created.




put
public abstract CharBuffer put( char c )

Relative put method  (optional operation).

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




put
public final CharBuffer put( char[] src )

Relative bulk put method  (optional operation).

This method transfers the entire content of the given source character 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)



put
public CharBuffer put( char[] src, int offset, int length )

Relative bulk put method  (optional operation).

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

Otherwise, this method copies length characters 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(a[i]);
except that it first checks that there is sufficient space in this buffer and it is potentially much more efficient.




put
public CharBuffer put( CharBuffer src )

Relative bulk put method  (optional operation).

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

Otherwise, this method copies n = src.remaining() characters 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.




put
public abstract CharBuffer put( int index, char c )

Absolute put method  (optional operation).

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




put
public final CharBuffer put( String src )

Relative bulk put method  (optional operation).

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

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



put
public CharBuffer put( String src, int start, int end )

Relative bulk put method  (optional operation).

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

Otherwise, this method copies n = end - start characters 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.




slice
public abstract CharBuffer slice( )

Creates a new character 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 characters remaining in this buffer, and its mark will be undefined. 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.




subSequence
public abstract CharSequence subSequence( int start, int end )

Creates a new character buffer that represents the specified subsequence of this buffer, relative to the current position.

The new buffer will share this buffer's content; that is, if the content of this buffer is mutable then modifications to one buffer will cause the other to be modified. The new buffer's capacity will be that of this buffer, its position will be position() + start, and its limit will be position() + end. 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.




toString
public String toString( )

Returns a string containing the characters in this buffer.

The first character of the resulting string will be the character at this buffer's position, while the last character will be the character at index limit() - 1. Invoking this method does not change the buffer's position.



Known Subclasses
 
None.



 
 
  dydoc
  3/10/05