jdk.nio.ByteBuffer — clojure-interop/java.nio 1.0.5

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.

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 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.

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);

*allocate clj

(*allocate capacity)

Allocates a new byte buffer.

The new buffer's position will be zero, its limit will be its capacity, its mark will be undefined, and each of its elements will be initialized to zero. It will have a backing array, and its array offset will be zero.

capacity - The new buffer's capacity, in bytes - int

returns: The new byte buffer - java.nio.ByteBuffer

throws: java.lang.IllegalArgumentException - If the capacity is a negative integer

*allocate-direct clj

(*allocate-direct capacity)

Allocates a new direct byte buffer.

The new buffer's position will be zero, its limit will be its capacity, its mark will be undefined, and each of its elements will be initialized to zero. Whether or not it has a backing array is unspecified.

capacity - The new buffer's capacity, in bytes - int

returns: The new byte buffer - java.nio.ByteBuffer

throws: java.lang.IllegalArgumentException - If the capacity is a negative integer

*wrap clj

(*wrap array)

(*wrap array offset 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.

array - The array that will back the new buffer - byte[] 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. - int 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. - int

returns: The new byte buffer - java.nio.ByteBuffer

throws: java.lang.IndexOutOfBoundsException - If the preconditions on the offset and length parameters do not hold

array clj

(array this)

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 - byte[]

throws: java.nio.ReadOnlyBufferException - If this buffer is backed by an array but is read-only

array-offset clj

(array-offset this)

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 - int

throws: java.nio.ReadOnlyBufferException - If this buffer is backed by an array but is read-only

as-char-buffer clj

(as-char-buffer this)

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.

returns: A new char buffer - java.nio.CharBuffer

as-double-buffer clj

(as-double-buffer this)

Creates a view of this byte buffer as a double 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 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.

returns: A new double buffer - java.nio.DoubleBuffer

as-float-buffer clj

(as-float-buffer this)

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 - java.nio.FloatBuffer

as-int-buffer clj

(as-int-buffer this)

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 - java.nio.IntBuffer

as-long-buffer clj

(as-long-buffer this)

Creates a view of this byte buffer as a long 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 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.

returns: A new long buffer - java.nio.LongBuffer

as-read-only-buffer clj

(as-read-only-buffer this)

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.

returns: The new, read-only byte buffer - java.nio.ByteBuffer

as-short-buffer clj

(as-short-buffer this)

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 - java.nio.ShortBuffer

compact clj

(compact this)

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 while (in.read(buf) >= 0 || buf.position != 0) { buf.flip(); out.write(buf); buf.compact(); // In case of partial write }

returns: This buffer - java.nio.ByteBuffer

throws: java.nio.ReadOnlyBufferException - If this buffer is read-only

compare-to clj

(compare-to this 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.

Pairs of byte elements are compared as if by invoking Byte.compare(byte,byte).

A byte buffer is not comparable to any other type of object.

that - the object to be compared. - java.nio.ByteBuffer

returns: A negative integer, zero, or a positive integer as this buffer is less than, equal to, or greater than the given buffer - int

direct? clj

(direct? this)

Tells whether or not this byte buffer is direct.

returns: true if, and only if, this buffer is direct - boolean

duplicate clj

(duplicate this)

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.

returns: The new byte buffer - java.nio.ByteBuffer

equals clj

(equals this 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.

ob - The object to which this buffer is to be compared - java.lang.Object

returns: true if, and only if, this buffer is equal to the given object - boolean

get clj

(get this)

(get this index)

(get this dst offset 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.

dst - The array into which bytes are to be written - byte[] offset - The offset within the array of the first byte to be written; must be non-negative and no larger than dst.length - int length - The maximum number of bytes to be written to the given array; must be non-negative and no larger than dst.length - offset - int

returns: This buffer - java.nio.ByteBuffer

throws: java.nio.BufferUnderflowException - If there are fewer than length bytes remaining in this buffer

get-char clj

(get-char this)

(get-char this 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.

index - The index from which the bytes will be read - int

returns: The char value at the given index - char

throws: java.lang.IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit, minus one

get-double clj

(get-double this)

(get-double this 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.

index - The index from which the bytes will be read - int

returns: The double value at the given index - double

throws: java.lang.IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit, minus seven

get-float clj

(get-float this)

(get-float this 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.

index - The index from which the bytes will be read - int

returns: The float value at the given index - float

throws: java.lang.IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit, minus three

get-int clj

(get-int this)

(get-int this 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.

index - The index from which the bytes will be read - int

returns: The int value at the given index - int

throws: java.lang.IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit, minus three

get-long clj

(get-long this)

(get-long this 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.

index - The index from which the bytes will be read - int

returns: The long value at the given index - long

throws: java.lang.IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit, minus seven

get-short clj

(get-short this)

(get-short this 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.

index - The index from which the bytes will be read - int

returns: The short value at the given index - short

throws: java.lang.IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit, minus one

has-array? clj

(has-array? this)

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 - boolean

hash-code clj

(hash-code this)

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 - int

order clj

(order this)

(order this bo)

Modifies this buffer's byte order.

bo - The new byte order, either BIG_ENDIAN or LITTLE_ENDIAN - java.nio.ByteOrder

returns: This buffer - java.nio.ByteBuffer

put clj

(put this b)

(put this index b)

(put this src offset 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.

src - The array from which bytes are to be read - byte[] offset - The offset within the array of the first byte to be read; must be non-negative and no larger than array.length - int length - The number of bytes to be read from the given array; must be non-negative and no larger than array.length - offset - int

returns: This buffer - java.nio.ByteBuffer

throws: java.nio.BufferOverflowException - If there is insufficient space in this buffer

put-char clj

(put-char this value)

(put-char this index 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.

index - The index at which the bytes will be written - int value - The char value to be written - char

returns: This buffer - java.nio.ByteBuffer

throws: java.lang.IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit, minus one

put-double clj

(put-double this value)

(put-double this index 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.

index - The index at which the bytes will be written - int value - The double value to be written - double

returns: This buffer - java.nio.ByteBuffer

throws: java.lang.IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit, minus seven

put-float clj

(put-float this value)

(put-float this index 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.

index - The index at which the bytes will be written - int value - The float value to be written - float

returns: This buffer - java.nio.ByteBuffer

throws: java.lang.IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit, minus three

put-int clj

(put-int this value)

(put-int this index 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.

index - The index at which the bytes will be written - int value - The int value to be written - int

returns: This buffer - java.nio.ByteBuffer

throws: java.lang.IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit, minus three

put-long clj

(put-long this value)

(put-long this index 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.

index - The index at which the bytes will be written - int value - The long value to be written - long

returns: This buffer - java.nio.ByteBuffer

throws: java.lang.IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit, minus seven

put-short clj

(put-short this value)

(put-short this index 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.

index - The index at which the bytes will be written - int value - The short value to be written - short

returns: This buffer - java.nio.ByteBuffer

throws: java.lang.IndexOutOfBoundsException - If index is negative or not smaller than the buffer's limit, minus one

slice clj

(slice this)

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 - java.nio.ByteBuffer

to-string clj

(to-string this)

Returns a string summarizing the state of this buffer.

returns: A summary string - java.lang.String