public abstract class

ByteBuffer

extends Buffer
java.lang.Object
   ↳ java.nio.Buffer
     ↳ java.nio.ByteBuffer

Class Overview

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;

  • Methods for creating view buffers, which allow a byte buffer to be viewed as a buffer containing values of some other primitive type; and

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.

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.

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: 

 float  getFloat()
 float  getFloat(int index)
  void  putFloat(float f)
  void  putFloat(int index, float 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.

View buffer

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);

Summary

Public Constructors
ByteBuffer()
Public Methods
static ByteBuffer allocateDirect(int capacity)
Allocates a new direct byte buffer.
final byte[] array()
Returns the byte array that backs this buffer  (optional operation).
final int arrayOffset()
Returns the offset within this buffer's backing array of the first element of the buffer  (optional operation).
abstract 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 ShortBuffer asShortBuffer()
Creates a view of this byte buffer as a short buffer.
int compareTo(ByteBuffer that)
Compares this buffer to another.
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, int offset, int length)
Relative bulk get method.
abstract byte get(int index)
Absolute get method.
ByteBuffer get(byte[] dst)
Relative bulk get method.
abstract float getFloat(int index)
Absolute get method for reading a float value.
abstract float getFloat()
Relative get method for reading a float value.
abstract int getInt(int index)
Absolute get method for reading an int value.
abstract int getInt()
Relative get method for reading an int 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.
final 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.
final ByteOrder order()
Retrieves this buffer's byte order.
final ByteBuffer order(ByteOrder bo)
Modifies this buffer's byte order.
abstract ByteBuffer put(byte b)
Relative put method  (optional operation).
ByteBuffer put(byte[] src, int offset, int length)
Relative bulk put method  (optional operation).
final ByteBuffer put(byte[] src)
Relative bulk put method  (optional operation).
abstract ByteBuffer put(int index, byte b)
Absolute put method  (optional operation).
ByteBuffer put(ByteBuffer src)
Relative bulk put method  (optional operation).
abstract ByteBuffer putFloat(int index, float value)
Absolute put method for writing a float value  (optional operation).
abstract ByteBuffer putFloat(float value)
Relative put method for writing a float value  (optional operation).
abstract ByteBuffer putInt(int index, int value)
Absolute put method for writing an int value  (optional operation).
abstract ByteBuffer putInt(int value)
Relative put method for writing an int value  (optional operation).
abstract ByteBuffer putShort(short value)
Relative put method for writing a short value  (optional operation).
abstract ByteBuffer putShort(int index, short value)
Absolute 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, int offset, int length)
Wraps a byte array into a buffer.
static ByteBuffer wrap(byte[] array)
Wraps a byte array into a buffer.
[Expand]
Inherited Methods
From class java.nio.Buffer
From class java.lang.Object

Public Constructors

public ByteBuffer ()

Public Methods

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 backing array is unspecified. @param capacity The new buffer's capacity, in bytes @return The new byte buffer @throws IllegalArgumentException If the capacity is a negative integer

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.

Returns
  • The array that backs this buffer

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.

Returns
  • The offset within this buffer's array of the first element of the buffer

public abstract FloatBuffer asFloatBuffer ()

Creates a view of this byte buffer as a float 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 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.

Returns
  • A new float buffer

public abstract IntBuffer asIntBuffer ()

Creates a view of this byte buffer as an int 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 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.

Returns
  • A new int buffer

public abstract ShortBuffer asShortBuffer ()

Creates a view of this byte buffer as a short 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.

Returns
  • A new short buffer

public int compareTo (ByteBuffer that)

Compares this buffer to another.

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.

Returns
  • A negative integer, zero, or a positive integer as this buffer is less than, equal to, or greater than the given buffer

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,

  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 byte buffer is not equal to any other type of object.

Parameters
ob The object to which this buffer is to be compared
Returns
  • true if, and only if, this buffer is equal to the given object

public abstract byte get ()

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

Returns
  • The byte at the buffer's current position
Throws
BufferUnderflowException If the buffer's current position is not smaller than its limit

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.

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

public abstract byte get (int index)

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

Parameters
index The index from which the byte will be read
Returns
  • The byte at the given index
Throws
IndexOutOfBoundsException If index is negative or not smaller than the buffer's limit

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)

Returns
  • This buffer
Throws
BufferUnderflowException If there are fewer than length bytes remaining in this buffer

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.

Parameters
index The index from which the bytes will be read
Returns
  • The float value at the given index
Throws
IndexOutOfBoundsException If index is negative or not smaller than the buffer's limit, minus three

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.

Returns
  • The float value at the buffer's current position
Throws
BufferUnderflowException If there are fewer than four bytes remaining in this buffer

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.

Parameters
index The index from which the bytes will be read
Returns
  • The int value at the given index
Throws
IndexOutOfBoundsException If index is negative or not smaller than the buffer's limit, minus three

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.

Returns
  • The int value at the buffer's current position
Throws
BufferUnderflowException If there are fewer than four bytes remaining in this buffer

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.

Returns
  • The short value at the buffer's current position
Throws
BufferUnderflowException If there are fewer than two bytes remaining in this buffer

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.

Parameters
index The index from which the bytes will be read
Returns
  • The short value at the given index
Throws
IndexOutOfBoundsException If index is negative or not smaller than the buffer's limit, minus one

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.

Returns
  • true if, and only if, this buffer is backed by an array and is not read-only

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.

Returns
  • The current hash code of this buffer

public abstract boolean isDirect ()

Tells whether or not this byte buffer is direct.

Returns
  • true if, and only if, this buffer is direct

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.

Returns
  • This buffer's byte order

public final ByteBuffer order (ByteOrder bo)

Modifies this buffer's byte order.

Parameters
bo The new byte order, either BIG_ENDIAN or LITTLE_ENDIAN
Returns
  • This buffer

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.

Parameters
b The byte to be written
Returns
  • This buffer
Throws
BufferOverflowException If this buffer's current position is not smaller than its limit

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.

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

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)

Returns
  • This buffer
Throws
BufferOverflowException If there is insufficient space in this buffer

public abstract ByteBuffer put (int index, byte b)

Absolute put method  (optional operation).

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

Parameters
index The index at which the byte will be written
b The byte value to be written
Returns
  • This buffer
Throws
IndexOutOfBoundsException If index is negative or not smaller than the buffer's limit

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.

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

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.

Parameters
index The index at which the bytes will be written
value The float value to be written
Returns
  • This buffer
Throws
IndexOutOfBoundsException If index is negative or not smaller than the buffer's limit, minus three

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.

Parameters
value The float value to be written
Returns
  • This buffer
Throws
BufferOverflowException If there are fewer than four bytes remaining in this buffer

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.

Parameters
index The index at which the bytes will be written
value The int value to be written
Returns
  • This buffer
Throws
IndexOutOfBoundsException If index is negative or not smaller than the buffer's limit, minus three

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.

Parameters
value The int value to be written
Returns
  • This buffer
Throws
BufferOverflowException If there are fewer than four bytes remaining in this buffer

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.

Parameters
value The short value to be written
Returns
  • This buffer
Throws
BufferOverflowException If there are fewer than two bytes remaining in this buffer

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.

Parameters
index The index at which the bytes will be written
value The short value to be written
Returns
  • This buffer
Throws
IndexOutOfBoundsException If index is negative or not smaller than the buffer's limit, minus one

public abstract ByteBuffer slice ()

Creates a new byte 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 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.

Returns
  • The new byte buffer

public String toString ()

Returns a string summarizing the state of this buffer.

Returns
  • A summary string

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 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.

@param array The array that will back the new buffer @param offset The offset of the subarray to be used; must be non-negative and no larger than array.length. The new buffer's position will be set to this value.

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

public static ByteBuffer wrap (byte[] array)

Wraps a byte array into a buffer.

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.

Parameters
array The array that will back this buffer
Returns
  • The new byte buffer