|
Préférences
Moteurs de recherche
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
JavaTM 2 Platform Std. Ed. v1.6.0
java.nio
|
Method Summary | |
---|---|
static ByteBuffer |
allocate(int capacity)
Allocates a new byte buffer. |
static ByteBuffer |
allocateDirect(int capacity)
Allocates a new direct byte buffer. |
byte[] |
array()
Returns the byte array that backs this buffer (optional operation). |
int |
arrayOffset()
Returns the offset within this buffer's backing array of the first element of the buffer (optional operation). |
abstract CharBuffer |
asCharBuffer()
Creates a view of this byte buffer as a char buffer. |
abstract DoubleBuffer |
asDoubleBuffer()
Creates a view of this byte buffer as a double buffer. |
abstract FloatBuffer |
asFloatBuffer()
Creates a view of this byte buffer as a float buffer. |
abstract IntBuffer |
asIntBuffer()
Creates a view of this byte buffer as an int buffer. |
abstract LongBuffer |
asLongBuffer()
Creates a view of this byte buffer as a long buffer. |
abstract ByteBuffer |
asReadOnlyBuffer()
Creates a new, read-only byte buffer that shares this buffer's content. |
abstract ShortBuffer |
asShortBuffer()
Creates a view of this byte buffer as a short buffer. |
abstract ByteBuffer |
compact()
Compacts this buffer (optional operation). |
int |
compareTo(ByteBuffer that)
Compares this buffer to another. |
abstract ByteBuffer |
duplicate()
Creates a new byte buffer that shares this buffer's content. |
boolean |
equals(Object ob)
Tells whether or not this buffer is equal to another object. |
abstract byte |
get()
Relative get method. |
ByteBuffer |
get(byte[] dst)
Relative bulk get method. |
ByteBuffer |
get(byte[] dst,
int offset,
int length)
Relative bulk get method. |
abstract byte |
get(int index)
Absolute get method. |
abstract char |
getChar()
Relative get method for reading a char value. |
abstract char |
getChar(int index)
Absolute get method for reading a char value. |
abstract double |
getDouble()
Relative get method for reading a double value. |
abstract double |
getDouble(int index)
Absolute get method for reading a double value. |
abstract float |
getFloat()
Relative get method for reading a float value. |
abstract float |
getFloat(int index)
Absolute get method for reading a float value. |
abstract int |
getInt()
Relative get method for reading an int value. |
abstract int |
getInt(int index)
Absolute get method for reading an int value. |
abstract long |
getLong()
Relative get method for reading a long value. |
abstract long |
getLong(int index)
Absolute get method for reading a long value. |
abstract short |
getShort()
Relative get method for reading a short value. |
abstract short |
getShort(int index)
Absolute get method for reading a short value. |
boolean |
hasArray()
Tells whether or not this buffer is backed by an accessible byte array. |
int |
hashCode()
Returns the current hash code of this buffer. |
abstract boolean |
isDirect()
Tells whether or not this byte buffer is direct. |
ByteOrder |
order()
Retrieves this buffer's byte order. |
ByteBuffer |
order(ByteOrder bo)
Modifies this buffer's byte order. |
abstract ByteBuffer |
put(byte b)
Relative put method (optional operation). |
ByteBuffer |
put(byte[] src)
Relative bulk put method (optional operation). |
ByteBuffer |
put(byte[] src,
int offset,
int length)
Relative bulk put method (optional operation). |
ByteBuffer |
put(ByteBuffer src)
Relative bulk put method (optional operation). |
abstract ByteBuffer |
put(int index,
byte b)
Absolute put method (optional operation). |
abstract ByteBuffer |
putChar(char value)
Relative put method for writing a char value (optional operation). |
abstract ByteBuffer |
putChar(int index,
char value)
Absolute put method for writing a char value (optional operation). |
abstract ByteBuffer |
putDouble(double value)
Relative put method for writing a double value (optional operation). |
abstract ByteBuffer |
putDouble(int index,
double value)
Absolute put method for writing a double value (optional operation). |
abstract ByteBuffer |
putFloat(float value)
Relative put method for writing a float value (optional operation). |
abstract ByteBuffer |
putFloat(int index,
float value)
Absolute put method for writing a float value (optional operation). |
abstract ByteBuffer |
putInt(int value)
Relative put method for writing an int value (optional operation). |
abstract ByteBuffer |
putInt(int index,
int value)
Absolute put method for writing an int value (optional operation). |
abstract ByteBuffer |
putLong(int index,
long value)
Absolute put method for writing a long value (optional operation). |
abstract ByteBuffer |
putLong(long value)
Relative put method for writing a long value (optional operation). |
abstract ByteBuffer |
putShort(int index,
short value)
Absolute put method for writing a short value (optional operation). |
abstract ByteBuffer |
putShort(short value)
Relative put method for writing a short value (optional operation). |
abstract ByteBuffer |
slice()
Creates a new byte buffer whose content is a shared subsequence of this buffer's content. |
String |
toString()
Returns a string summarizing the state of this buffer. |
static ByteBuffer |
wrap(byte[] array)
Wraps a byte array into a buffer. |
static ByteBuffer |
wrap(byte[] array,
int offset,
int length)
Wraps a byte array into a buffer. |
Methods inherited from class java.nio.Buffer |
---|
capacity, clear, flip, hasRemaining, isReadOnly, limit, limit, mark, position, position, remaining, reset, rewind |
Methods inherited from class java.lang.Object |
---|
clone, finalize, getClass, notify, notifyAll, wait, wait, wait |
Method Detail |
---|
public static ByteBuffer allocateDirect(int capacity)
The new buffer's position will be zero, its limit will be its
capacity, and its mark will be undefined. Whether or not it has a
backing array
is unspecified.
capacity
- The new buffer's capacity, in bytes
IllegalArgumentException
- If the capacity is a negative integerpublic static ByteBuffer allocate(int capacity)
The new buffer's position will be zero, its limit will be its
capacity, and its mark will be undefined. It will have a backing array
, and its
array
offset
will be zero.
capacity
- The new buffer's capacity, in bytes
IllegalArgumentException
- If the capacity is a negative integerpublic static ByteBuffer wrap(byte[] array, int offset, int length)
The new buffer will be backed by the given byte 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
backing array
will be the given array, and
its
array offset
will be zero.
array
- The array that will back the new bufferoffset
- 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.
IndexOutOfBoundsException
- If the preconditions on the offset and length
parameters do not holdpublic static ByteBuffer wrap(byte[] array)
The new buffer will be backed by the given byte 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 backing array
will be the
given array, and its
array offset
will
be zero.
array
- The array that will back this buffer
public abstract ByteBuffer slice()
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 bytes 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.
public abstract ByteBuffer duplicate()
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.
public abstract ByteBuffer asReadOnlyBuffer()
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.
public abstract byte get()
BufferUnderflowException
- If the buffer's current position is not smaller than its limitpublic abstract ByteBuffer put(byte b)
Writes the given byte into this buffer at the current position, and then increments the position.
b
- The byte to be written
BufferOverflowException
- If this buffer's current position is not smaller than its limit
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract byte get(int index)
index
- The index from which the byte will be read
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limitpublic abstract ByteBuffer put(int index, byte b)
Writes the given byte into this buffer at the given index.
index
- The index at which the byte will be writtenb
- The byte value to be written
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limit
ReadOnlyBufferException
- If this buffer is read-onlypublic ByteBuffer get(byte[] dst, int offset, int length)
This method transfers bytes from this buffer into the given
destination array. If there are fewer bytes remaining in the
buffer than are required to satisfy the request, that is, if
length > remaining(), then no
bytes are transferred and a BufferUnderflowException
is
thrown.
Otherwise, this method copies length bytes 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 bytes in this buffer and it is potentially much more efficient.
dst
- The array into which bytes are to be writtenoffset
- The offset within the array of the first byte to be
written; must be non-negative and no larger than
dst.lengthlength
- The maximum number of bytes to be written to the given
array; must be non-negative and no larger than
dst.length - offset
BufferUnderflowException
- If there are fewer than length bytes
remaining in this buffer
IndexOutOfBoundsException
- If the preconditions on the offset and length
parameters do not holdpublic ByteBuffer get(byte[] dst)
This method transfers bytes 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)
BufferUnderflowException
- If there are fewer than length bytes
remaining in this bufferpublic ByteBuffer put(ByteBuffer src)
This method transfers the bytes remaining in the given source
buffer into this buffer. If there are more bytes remaining in the
source buffer than in this buffer, that is, if
src.remaining() > remaining(),
then no bytes are transferred and a BufferOverflowException
is thrown.
Otherwise, this method copies n = src.remaining() bytes 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.
src
- The source buffer from which bytes are to be read;
must not be this buffer
BufferOverflowException
- If there is insufficient space in this buffer
for the remaining bytes in the source buffer
IllegalArgumentException
- If the source buffer is this buffer
ReadOnlyBufferException
- If this buffer is read-onlypublic ByteBuffer put(byte[] src, int offset, int length)
This method transfers bytes into this buffer from the given
source array. If there are more bytes to be copied from the array
than remain in this buffer, that is, if
length > remaining(), then no
bytes are transferred and a BufferOverflowException
is
thrown.
Otherwise, this method copies length bytes 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.
src
- The array from which bytes are to be readoffset
- The offset within the array of the first byte to be read;
must be non-negative and no larger than array.lengthlength
- The number of bytes to be read from the given array;
must be non-negative and no larger than
array.length - offset
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-onlypublic final ByteBuffer put(byte[] src)
This method transfers the entire content of the given source byte 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)
BufferOverflowException
- If there is insufficient space in this buffer
ReadOnlyBufferException
- If this buffer is read-onlypublic final boolean hasArray()
If this method returns true then the array
and arrayOffset
methods may safely be invoked.
public final byte[] array()
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.
ReadOnlyBufferException
- If this buffer is backed by an array but is read-only
UnsupportedOperationException
- If this buffer is not backed by an accessible arraypublic final int arrayOffset()
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.
arrayOffset
in class Buffer
ReadOnlyBufferException
- If this buffer is backed by an array but is read-only
UnsupportedOperationException
- If this buffer is not backed by an accessible arraypublic abstract ByteBuffer compact()
The bytes between the buffer's current position and its limit, if any, are copied to the beginning of the buffer. That is, the byte at index p = position() is copied to index zero, the byte at index p + 1 is copied to index one, and so forth until the byte 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 bytes copied, rather than to zero, so that an invocation of this method can be followed immediately by an invocation of another relative put method.
Invoke this method after writing data from a buffer in case the write was incomplete. The following loop, for example, copies bytes from one channel to another via the buffer buf:
buf.clear(); // Prepare buffer for use while (in.read(buf) >= 0 || buf.position != 0) { buf.flip(); out.write(buf); buf.compact(); // In case of partial write }
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract boolean isDirect()
public String toString()
public int hashCode()
The hash code of a byte 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.
Object.equals(java.lang.Object)
,
Hashtable
public boolean equals(Object ob)
Two byte buffers are equal if, and only if,
They have the same element type,
They have the same number of remaining elements, and
The two sequences of remaining elements, considered independently of their starting positions, are pointwise equal.
A byte buffer is not equal to any other type of object.
ob
- The object to which this buffer is to be compared
Object.hashCode()
,
Hashtable
public int compareTo(ByteBuffer that)
Two byte 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 byte buffer is not comparable to any other type of object.
compareTo
in interface Comparable<ByteBuffer>
that
- the object to be compared.
public final ByteOrder order()
The byte order is used when reading or writing multibyte values, and
when creating buffers that are views of this byte buffer. The order of
a newly-created byte buffer is always BIG_ENDIAN
.
public final ByteBuffer order(ByteOrder bo)
bo
- The new byte order,
either BIG_ENDIAN
or LITTLE_ENDIAN
public abstract char getChar()
Reads the next two bytes at this buffer's current position, composing them into a char value according to the current byte order, and then increments the position by two.
BufferUnderflowException
- If there are fewer than two bytes
remaining in this bufferpublic abstract ByteBuffer putChar(char value)
Writes two bytes containing the given char value, in the current byte order, into this buffer at the current position, and then increments the position by two.
value
- The char value to be written
BufferOverflowException
- If there are fewer than two bytes
remaining in this buffer
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract char getChar(int index)
Reads two bytes at the given index, composing them into a char value according to the current byte order.
index
- The index from which the bytes will be read
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limit,
minus onepublic abstract ByteBuffer putChar(int index, char value)
Writes two bytes containing the given char value, in the current byte order, into this buffer at the given index.
index
- The index at which the bytes will be writtenvalue
- The char value to be written
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limit,
minus one
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract CharBuffer asCharBuffer()
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 bytes remaining in this buffer divided by two, 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.
public abstract short getShort()
Reads the next two bytes at this buffer's current position, composing them into a short value according to the current byte order, and then increments the position by two.
BufferUnderflowException
- If there are fewer than two bytes
remaining in this bufferpublic abstract ByteBuffer putShort(short value)
Writes two bytes containing the given short value, in the current byte order, into this buffer at the current position, and then increments the position by two.
value
- The short value to be written
BufferOverflowException
- If there are fewer than two bytes
remaining in this buffer
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract short getShort(int index)
Reads two bytes at the given index, composing them into a short value according to the current byte order.
index
- The index from which the bytes will be read
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limit,
minus onepublic abstract ByteBuffer putShort(int index, short value)
Writes two bytes containing the given short value, in the current byte order, into this buffer at the given index.
index
- The index at which the bytes will be writtenvalue
- The short value to be written
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limit,
minus one
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract ShortBuffer asShortBuffer()
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 bytes remaining in this buffer divided by two, 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.
public abstract int getInt()
Reads the next four bytes at this buffer's current position, composing them into an int value according to the current byte order, and then increments the position by four.
BufferUnderflowException
- If there are fewer than four bytes
remaining in this bufferpublic abstract ByteBuffer putInt(int value)
Writes four bytes containing the given int value, in the current byte order, into this buffer at the current position, and then increments the position by four.
value
- The int value to be written
BufferOverflowException
- If there are fewer than four bytes
remaining in this buffer
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract int getInt(int index)
Reads four bytes at the given index, composing them into a int value according to the current byte order.
index
- The index from which the bytes will be read
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limit,
minus threepublic abstract ByteBuffer putInt(int index, int value)
Writes four bytes containing the given int value, in the current byte order, into this buffer at the given index.
index
- The index at which the bytes will be writtenvalue
- The int value to be written
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limit,
minus three
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract IntBuffer asIntBuffer()
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 bytes remaining in this buffer divided by four, 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.
public abstract long getLong()
Reads the next eight bytes at this buffer's current position, composing them into a long value according to the current byte order, and then increments the position by eight.
BufferUnderflowException
- If there are fewer than eight bytes
remaining in this bufferpublic abstract ByteBuffer putLong(long value)
Writes eight bytes containing the given long value, in the current byte order, into this buffer at the current position, and then increments the position by eight.
value
- The long value to be written
BufferOverflowException
- If there are fewer than eight bytes
remaining in this buffer
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract long getLong(int index)
Reads eight bytes at the given index, composing them into a long value according to the current byte order.
index
- The index from which the bytes will be read
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limit,
minus sevenpublic abstract ByteBuffer putLong(int index, long value)
Writes eight bytes containing the given long value, in the current byte order, into this buffer at the given index.
index
- The index at which the bytes will be writtenvalue
- The long value to be written
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limit,
minus seven
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract LongBuffer asLongBuffer()
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 bytes remaining in this buffer divided by eight, 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.
public abstract float getFloat()
Reads the next four bytes at this buffer's current position, composing them into a float value according to the current byte order, and then increments the position by four.
BufferUnderflowException
- If there are fewer than four bytes
remaining in this bufferpublic abstract ByteBuffer putFloat(float value)
Writes four bytes containing the given float value, in the current byte order, into this buffer at the current position, and then increments the position by four.
value
- The float value to be written
BufferOverflowException
- If there are fewer than four bytes
remaining in this buffer
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract float getFloat(int index)
Reads four bytes at the given index, composing them into a float value according to the current byte order.
index
- The index from which the bytes will be read
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limit,
minus threepublic abstract ByteBuffer putFloat(int index, float value)
Writes four bytes containing the given float value, in the current byte order, into this buffer at the given index.
index
- The index at which the bytes will be writtenvalue
- The float value to be written
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limit,
minus three
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract FloatBuffer asFloatBuffer()
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 bytes remaining in this buffer divided by four, 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.
public abstract double getDouble()
Reads the next eight bytes at this buffer's current position, composing them into a double value according to the current byte order, and then increments the position by eight.
BufferUnderflowException
- If there are fewer than eight bytes
remaining in this bufferpublic abstract ByteBuffer putDouble(double value)
Writes eight bytes containing the given double value, in the current byte order, into this buffer at the current position, and then increments the position by eight.
value
- The double value to be written
BufferOverflowException
- If there are fewer than eight bytes
remaining in this buffer
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract double getDouble(int index)
Reads eight bytes at the given index, composing them into a double value according to the current byte order.
index
- The index from which the bytes will be read
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limit,
minus sevenpublic abstract ByteBuffer putDouble(int index, double value)
Writes eight bytes containing the given double value, in the current byte order, into this buffer at the given index.
index
- The index at which the bytes will be writtenvalue
- The double value to be written
IndexOutOfBoundsException
- If index is negative
or not smaller than the buffer's limit,
minus seven
ReadOnlyBufferException
- If this buffer is read-onlypublic abstract DoubleBuffer asDoubleBuffer()
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 bytes remaining in this buffer divided by eight, 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.