java.nio.ByteBuffer

Documentation › java.nio › ByteBuffer

	*ByteBuffer*
	`public abstract`

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

Class Description

A byte buffer.

This class defines six categories of operations upon byte buffers:

Absolute and relative getandputmethods that read and write single bytes;

 

 Relative get 
methods that transfer contiguous sequences of bytes from this buffer 
into an array; 
 

 Relative 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. 











 
 Direct vs. non-direct buffers 
 

 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. 


 
 Access to binary data 
 

 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 heterogenous 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: 

 
float getFloat() 
float index) 
void f) 
void f) 

 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.  

























 Invocation chaining  


 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 

 
bb.putInt(0xCAFEBABE); 
bb.putShort(3); 
bb.putShort(45); 

can, for example, be replaced by the single statement 

 
bb.putInt(0xCAFEBABE).putShort(3).putShort(45);

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 ByteBuffer allocate( int capacity )

Allocates a new byte 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. allocateDirect public static ByteBuffer allocateDirect( int capacity ) Allocates a new direct byte buffer.

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 array is unspecified.







wrap


public static ByteBuffer wrap(
byte[] array
)





Wraps a byte array into a buffer. 

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






wrap


public static ByteBuffer wrap(
byte[] array, 
int offset, 
int length
)





Wraps a byte array into a buffer. 

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

Instance Methods

array
public final byte[] array( )

Returns the byte 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.

asCharBuffer
public abstract CharBuffer asCharBuffer( )

Creates a view of this byte buffer as a char buffer.

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.

asDoubleBuffer
public abstract DoubleBuffer asDoubleBuffer( )

Creates a view of this byte buffer as a double buffer.

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.

asFloatBuffer
public abstract FloatBuffer asFloatBuffer( )

Creates a view of this byte buffer as a float buffer.

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.

asIntBuffer
public abstract IntBuffer asIntBuffer( )

Creates a view of this byte buffer as an int buffer.

asLongBuffer
public abstract LongBuffer asLongBuffer( )

Creates a view of this byte buffer as a long buffer.

asReadOnlyBuffer
public abstract ByteBuffer asReadOnlyBuffer( )

Creates a new, read-only byte 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.

asShortBuffer
public abstract ShortBuffer asShortBuffer( )

Creates a view of this byte buffer as a short buffer.

compact
public abstract ByteBuffer compact( )

Compacts this buffer (optional operation).

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 
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 
}

compareTo
public int compareTo( Object ob )

Compares this buffer to another object.

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.

duplicate
public abstract ByteBuffer duplicate( )

Creates a new byte 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 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.

get
public abstract byte get( )

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

get
public ByteBuffer get( byte[] dst )

Relative bulk get method.

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)

get
public ByteBuffer get( byte[] dst, int offset, int length )

Relative bulk get method.

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.

get
public abstract byte get( int index )

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

getChar
public abstract char getChar( )

Relative get method for reading a char value.

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.

getChar
public abstract char getChar( int index )

Absolute get method for reading a char value.

Reads two bytes at the given index, composing them into a char value according to the current byte order.

getDouble
public abstract double getDouble( )

Relative get method for reading a double value.

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.

getDouble
public abstract double getDouble( int index )

Absolute get method for reading a double value.

Reads eight bytes at the given index, composing them into a double value according to the current byte order.

getFloat
public abstract float getFloat( )

Relative get method for reading a float value.

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.

getFloat
public abstract float getFloat( int index )

Absolute get method for reading a float value.

Reads four bytes at the given index, composing them into a float value according to the current byte order.

getInt
public abstract int getInt( )

Relative get method for reading an int value.

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.

getInt
public abstract int getInt( int index )

Absolute get method for reading an int value.

Reads four bytes at the given index, composing them into a int value according to the current byte order.

getLong
public abstract long getLong( )

Relative get method for reading a long value.

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.

getLong
public abstract long getLong( int index )

Absolute get method for reading a long value.

Reads eight bytes at the given index, composing them into a long value according to the current byte order.

getShort
public abstract short getShort( )

Relative get method for reading a short value.

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.

getShort
public abstract short getShort( int index )

Absolute get method for reading a short value.

Reads two bytes at the given index, composing them into a short value according to the current byte order.

hasArray
public final boolean hasArray( )

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

isDirect
public abstract boolean isDirect( )

Tells whether or not this byte buffer is direct.

order
public final ByteOrder order( )

Retrieves this buffer's byte 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.

order
public final ByteBuffer order( ByteOrder bo )

Modifies this buffer's byte order.

put
public abstract ByteBuffer put( byte b )

Relative put method (optional operation).

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

put
public final ByteBuffer put( byte[] src )

Relative bulk put method (optional operation).

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)

put
public ByteBuffer put( byte[] src, int offset, int length )

Relative bulk put method (optional operation).

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.

put
public ByteBuffer put( ByteBuffer src )

Relative bulk put method (optional operation).

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.

put
public abstract ByteBuffer put( int index, byte b )

Absolute put method (optional operation).

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

putChar
public abstract ByteBuffer putChar( char value )

Relative put method for writing a char value (optional operation).

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.

putChar
public abstract ByteBuffer putChar( int index, char value )

Absolute put method for writing a char value (optional operation).

Writes two bytes containing the given char value, in the current byte order, into this buffer at the given index.

putDouble
public abstract ByteBuffer putDouble( double value )

Relative put method for writing a double value (optional operation).

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.

putDouble
public abstract ByteBuffer putDouble( int index, double value )

Absolute put method for writing a double value (optional operation).

Writes eight bytes containing the given double value, in the current byte order, into this buffer at the given index.

putFloat
public abstract ByteBuffer putFloat( float value )

Relative put method for writing a float value (optional operation).

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.

putFloat
public abstract ByteBuffer putFloat( int index, float value )

Absolute put method for writing a float value (optional operation).

Writes four bytes containing the given float value, in the current byte order, into this buffer at the given index.

putInt
public abstract ByteBuffer putInt( int value )

Relative put method for writing an int value (optional operation).

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.

putInt
public abstract ByteBuffer putInt( int index, int value )

Absolute put method for writing an int value (optional operation).

Writes four bytes containing the given int value, in the current byte order, into this buffer at the given index.

putLong
public abstract ByteBuffer putLong( int index, long value )

Absolute put method for writing a long value (optional operation).

Writes eight bytes containing the given long value, in the current byte order, into this buffer at the given index.

putLong
public abstract ByteBuffer putLong( long value )

Relative put method for writing a long value (optional operation).

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.

putShort
public abstract ByteBuffer putShort( int index, short value )

Absolute put method for writing a short value (optional operation).

Writes two bytes containing the given short value, in the current byte order, into this buffer at the given index.

putShort
public abstract ByteBuffer putShort( short value )

Relative put method for writing a short value (optional operation).

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.

slice
public abstract ByteBuffer slice( )

Creates a new byte buffer whose content is a shared subsequence of this buffer's content.

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.

toString
public String toString( )

Returns a string summarizing the state of this buffer.

Known Subclasses
	MappedByteBuffer

	dydoc
	3/10/05

`Direct vs. non-direct buffers`

`Access to binary data`

Invocation chaining