java.lang.Object java.nio.Buffer java.nio.ByteBuffer
public abstract class ByteBuffer
A byte buffer.
This class defines six categories of operations upon byte buffers:
Absolute and relative get and put methods that read and write single bytes;
Relative bulk get methods that transfer contiguous sequences of bytes from this buffer into an array;
Relative bulk put methods that transfer contiguous sequences of bytes from a byte array or some other byte buffer into this buffer;
Absolute and relative get and put methods that read and write values of other primitive types, translating them to and from sequences of bytes in a particular byte order;
Methods for creating view buffers , which allow a byte buffer to be viewed as a buffer containing values of some other primitive type; and
Methods for compacting , duplicating , and slicing a byte buffer.
Byte buffers can be created either by
allocation
, which allocates space for the buffer's content, or by
wrapping
an existing byte array into a buffer.
A byte buffer is either
direct
or
non-direct
. Given a direct byte buffer, the Java virtual machine will make a best effort to perform native I/O operations directly upon it. That is, it will attempt to avoid copying the buffer's content to (or from) an intermediate buffer before (or after) each invocation of one of the underlying operating system's native I/O operations.
A direct byte buffer may be created by invoking the
allocateDirect
factory method of this class. The buffers returned by this method typically have somewhat higher allocation and deallocation costs than non-direct buffers. The contents of direct buffers may reside outside of the normal garbage-collected heap, and so their impact upon the memory footprint of an application might not be obvious. It is therefore recommended that direct buffers be allocated primarily for large, long-lived buffers that are subject to the underlying system's native I/O operations. In general it is best to allocate direct buffers only when they yield a measureable gain in program performance.
A direct byte buffer may also be created by
mapping
a region of a file directly into memory. An implementation of the Java platform may optionally support the creation of direct byte buffers from native code via JNI. If an instance of one of these kinds of buffers refers to an inaccessible region of memory then an attempt to access that region will not change the buffer's content and will cause an unspecified exception to be thrown either at the time of the access or at some later time.
Whether a byte buffer is direct or non-direct may be determined by invoking its
isDirect
method. This method is provided so that explicit buffer management can be done in performance-critical code.
This class defines methods for reading and writing values of all other primitive types, except
boolean
. Primitive values are translated to (or from) sequences of bytes according to the buffer's current byte order, which may be retrieved and modified via the
order
methods. Specific byte orders are represented by instances of the
ByteOrder
class. The initial order of a byte buffer is always
BIG_ENDIAN
.
For access to heterogeneous binary data, that is, sequences of values of different types, this class defines a family of absolute and relative
get
and
put
methods for each type. For 32-bit floating-point values, for example, this class defines:
Corresponding methods are defined for the types
char
,
short
,
int
,
long
, and
double
. The index parameters of the absolute
get
and
put
methods are in terms of bytes rather than of the type being read or written.
For access to homogeneous binary data, that is, sequences of values of the same type, this class defines methods that can create
views
of a given byte buffer. A
view buffer
is simply another buffer whose content is backed by the byte buffer. Changes to the byte buffer's content will be visible in the view buffer, and vice versa; the two buffers' position, limit, and mark values are independent. The
asFloatBuffer
method, for example, creates an instance of the
FloatBuffer
class that is backed by the byte buffer upon which the method is invoked. Corresponding view-creation methods are defined for the types
char
,
short
,
int
,
long
, and
double
.
View buffers have three important advantages over the families of type-specific
get
and
put
methods described above:
A view buffer is indexed not in terms of bytes but rather in terms of the type-specific size of its values;
A view buffer provides relative bulk
get
and
put
methods that can transfer contiguous sequences of values between a buffer and an array or some other buffer of the same type; and
A view buffer is potentially much more efficient because it will be direct if, and only if, its backing byte buffer is direct.
The byte order of a view buffer is fixed to be that of its byte buffer at the time that the view is created.
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
Direct
vs.
non-direct buffers
Access to binary data
float getFloat()
float getFloat(int index)
void putFloat(float f)
void putFloat(int index, float f)
Invocation chaining
can, for example, be replaced by the single statement
bb.putInt(0xCAFEBABE);
bb.putShort(3);
bb.putShort(45);
bb.putInt(0xCAFEBABE).putShort(3).putShort(45);
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.
public 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.
public 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.
public 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.
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()
public abstract ByteBuffer put(byte b)
Writes the given byte into this buffer at the current position, and then increments the position.
public abstract byte get(int index)
public abstract ByteBuffer put(int index, byte b)
Writes the given byte into this buffer at the given index.
public 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.
public 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)
public 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.
public 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.
public 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)
public 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.
public 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.
public 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 }buf.clear(); // Prepare buffer for use for (;;) { if (in.read(buf)< 0 && !buf.hasRemaining()) break; // No more bytes to transfer buf.flip(); out.write(buf); buf.compact(); // In case of partial write }
public 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.
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.
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.
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)
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.
public 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.
public abstract char getChar(int index)
Reads two bytes at the given index, composing them into a char value according to the current byte order.
public 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.
public 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.
public 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.
public abstract short getShort(int index)
Reads two bytes at the given index, composing them into a short value according to the current byte order.
public 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.
public 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.
public 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.
public abstract int getInt(int index)
Reads four bytes at the given index, composing them into a int value according to the current byte order.
public 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.
public 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.
public 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.
public abstract long getLong(int index)
Reads eight bytes at the given index, composing them into a long value according to the current byte order.
public 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.
public 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.
public 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.
public abstract float getFloat(int index)
Reads four bytes at the given index, composing them into a float value according to the current byte order.
public 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.
public 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.
public 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.
public abstract double getDouble(int index)
Reads eight bytes at the given index, composing them into a double value according to the current byte order.
public 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.
public 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.