Buffer

public abstract class Buffer extends Object
Known Direct Subclasses
Known Indirect Subclasses

A container for data of a specific primitive type.

A buffer is a linear, finite sequence of elements of a specific primitive type. Aside from its content, the essential properties of a buffer are its capacity, limit, and position:

A buffer's capacity is the number of elements it contains. The capacity of a buffer is never negative and never changes.

A buffer's limit is the index of the first element that should not be read or written. A buffer's limit is never negative and is never greater than its capacity.

A buffer's position is the index of the next element to be read or written. A buffer's position is never negative and is never greater than its limit.

There is one subclass of this class for each non-boolean primitive type.

Transferring data

Each subclass of this class defines two categories of get and put operations:

Relative operations read or write one or more elements starting at the current position and then increment the position by the number of elements transferred. If the requested transfer exceeds the limit then a relative get operation throws a BufferUnderflowException and a relative put operation throws a BufferOverflowException; in either case, no data is transferred.

Absolute operations take an explicit element index and do not affect the position. Absolute get and put operations throw an IndexOutOfBoundsException if the index argument exceeds the limit.

Data may also, of course, be transferred in to or out of a buffer by the I/O operations of an appropriate channel, which are always relative to the current position.

Marking and resetting

A buffer's mark is the index to which its position will be reset when the reset method is invoked. The mark is not always defined, but when it is defined it is never negative and is never greater than the position. If the mark is defined then it is discarded when the position or the limit is adjusted to a value smaller than the mark. If the mark is not defined then invoking the reset method causes an InvalidMarkException to be thrown.

Invariants

The following invariant holds for the mark, position, limit, and capacity values:

0 <= mark <= position <= limit <= capacity

A newly-created buffer always has a position of zero and a mark that is undefined. The initial limit may be zero, or it may be some other value that depends upon the type of the buffer and the manner in which it is constructed. Each element of a newly-allocated buffer is initialized to zero.

Clearing, flipping, and rewinding

In addition to methods for accessing the position, limit, and capacity values and for marking and resetting, this class also defines the following operations upon buffers:

  • clear() makes a buffer ready for a new sequence of channel-read or relative put operations: It sets the limit to the capacity and the position to zero.

  • flip() makes a buffer ready for a new sequence of channel-write or relative get operations: It sets the limit to the current position and then sets the position to zero.

  • rewind() makes a buffer ready for re-reading the data that it already contains: It leaves the limit unchanged and sets the position to zero.

Read-only buffers

Every buffer is readable, but not every buffer is writable. The mutation methods of each buffer class are specified as optional operations that will throw a ReadOnlyBufferException when invoked upon a read-only buffer. A read-only buffer does not allow its content to be changed, but its mark, position, and limit values are mutable. Whether or not a buffer is read-only may be determined by invoking its isReadOnly method.

Thread safety

Buffers are not safe for use by multiple concurrent threads. If a buffer is to be used by more than one thread then access to the buffer should be controlled by appropriate synchronization.

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; for example, the sequence of statements

 b.flip();
 b.position(23);
 b.limit(42);
can be replaced by the single, more compact statement
 b.flip().position(23).limit(42);

Public Method Summary

abstract Object
array()
Returns the array that backs this buffer  (optional operation).
abstract int
arrayOffset()
Returns the offset within this buffer's backing array of the first element of the buffer  (optional operation).
final int
capacity()
Returns this buffer's capacity.
final Buffer
clear()
Clears this buffer.
final Buffer
flip()
Flips this buffer.
abstract boolean
hasArray()
Tells whether or not this buffer is backed by an accessible array.
final boolean
hasRemaining()
Tells whether there are any elements between the current position and the limit.
abstract boolean
isDirect()
Tells whether or not this buffer is direct.
abstract boolean
isReadOnly()
Tells whether or not this buffer is read-only.
final int
limit()
Returns this buffer's limit.
final Buffer
limit(int newLimit)
Sets this buffer's limit.
final Buffer
mark()
Sets this buffer's mark at its position.
final Buffer
position(int newPosition)
Sets this buffer's position.
final int
position()
Returns this buffer's position.
final int
remaining()
Returns the number of elements between the current position and the limit.
final Buffer
reset()
Resets this buffer's position to the previously-marked position.
final Buffer
rewind()
Rewinds this buffer.

Inherited Method Summary