Class ByteBuffer

java.lang.Object
javacardx.framework.nio.Buffer
javacardx.framework.nio.ByteBuffer
public abstract class ByteBuffer extends Buffer
A byte buffer.

This class defines five 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 compacting 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 measurable 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

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 integer values, for example, this class defines: 

int  getInt()
int getInt(int index)
void putInt(int f)
void putInt(int index, int i)

Corresponding methods are defined for the type short . The index parameters of the absolute get and put methods are in terms of bytes rather than of the type being read or written.

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);

Since:
3.1

  • Method Summary

    Modifier and Type
    Method
    Description
    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 ByteBuffer
    asReadOnlyBuffer()
    Creates a new, read-only byte buffer that shares this buffer's content.
    abstract ByteBuffer
    compact()
    Compacts this buffer  (optional operation).
    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)
    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 int
    getInt()
    Relative get method for reading an int value.
    abstract int
    getInt(int index)
    Absolute 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.
    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)
    Relative bulk put method  (optional operation).
    ByteBuffer
    put(byte[] src, int offset, int length)
    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
    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
    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.
    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 Buffer

    capacity, clear, flip, hasRemaining, isReadOnly, limit, limit, position, position, remaining, rewind
    Modifier and Type
    Method
    Description
    final int
    capacity()
    Returns this buffer's capacity.
    final Buffer
    clear()
    Clears this buffer.
    final Buffer
    flip()
    Flips this buffer.
    final boolean
    hasRemaining()
    Tells whether there are any elements between the current position and the limit.
    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 int
    position()
    Returns this buffer's position.
    final Buffer
    position(int newPosition)
    Sets this buffer's position.
    final int
    remaining()
    Returns the number of elements between the current position and the limit.
    final Buffer
    rewind()
    Rewinds this buffer.

  • Method Details

    • 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, each of its elements will be initialized to zero, and its byte order will be BIG_ENDIAN. Whether or not it has a backing array is unspecified.

      Parameters:
      capacity - The new buffer's capacity, in bytes.
      Returns:
      The new byte buffer.
      Throws:
      SystemException - with the following reason codes

    • 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 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 byte order will be BIG_ENDIAN. Its backing array will be the given array, and its array offset will be zero.

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

    • wrap

      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 byte order will be BIG_ENDIAN. 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.

    • 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.

      Returns:
      This buffer's byte order

    • 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

    • 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.

      Specified by:
      hasArray in class Buffer
      Returns:
      true if, and only if, this buffer is backed by an array

    • 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.

      Specified by:
      array in class Buffer
      Returns:
      The array that backs this buffer
      Throws:
      SystemException - If this buffer is not backed by an accessible array
      ReadOnlyBufferException - If this buffer is read-only

    • 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.

      Specified by:
      arrayOffset in class Buffer
      Returns:
      The offset within this buffer's array of the first element of the buffer
      Throws:
      SystemException - If this buffer is not backed by an accessible array
      ReadOnlyBufferException - If this buffer is read-only

    • isDirect

      public abstract boolean isDirect()
      Tells whether or not this byte buffer is direct.
      Specified by:
      isDirect in class Buffer
      Returns:
      true if, and only if, this buffer is direct

    • 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,

      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.

      Overrides:
      equals in class 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

    • compareTo

      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.

      Parameters:
      that - the object to be compared.
      Returns:
      A negative integer, zero, or a positive integer as this buffer is less than, equal to, or greater than the given buffer.

    • 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 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 nonnegative and no larger than dst.length.
      length - The maximum number of bytes to be written to the given array; must be nonnegative 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.

    • 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 the same way as the invocation 

      src.get(a, 0, a.length)

      Parameters:
      dst - The array into which bytes are to be written
      Returns:
      This buffer.
      Throws:
      BufferUnderflowException - If there are fewer than dst.length bytes remaining in this buffer.

    • 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 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
      SystemException - with reason code SystemException.ILLEGAL_VALUE if the src buffer is this buffer
      ReadOnlyBufferException - If this buffer is read-only

    • put

      public 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 the same way as the invocation 

      dst.put(a, 0, a.length)

      Parameters:
      src - The array from which bytes are to be read
      Returns:
      This buffer
      Throws:
      BufferOverflowException - If there is insufficient space in this buffer
      ReadOnlyBufferException - If this buffer is read-only

    • 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 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 nonnegative and no larger than array.length
      length - The number of bytes to be read from the given array; must be nonnegative 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
      ReadOnlyBufferException - If this buffer is read-only

    • get

      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

    • 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.

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

    • get

      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

    • 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.

      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
      ReadOnlyBufferException - If this buffer is read-only

    • 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.

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

    • 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.

      Parameters:
      value - The short value to be written
      Returns:
      This buffer
      Throws:
      BufferOverflowException - If there are fewer than two bytes remaining in this buffer
      ReadOnlyBufferException - If this buffer is read-only

    • 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.

      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

    • 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.

      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
      ReadOnlyBufferException - If this buffer is read-only

    • 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.

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

    • 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.

      Parameters:
      value - The int value to be written
      Returns:
      This buffer
      Throws:
      BufferOverflowException - If there are fewer than four bytes remaining in this buffer
      ReadOnlyBufferException - If this buffer is read-only

    • 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.

      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

    • 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.

      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
      ReadOnlyBufferException - If this buffer is read-only

    • 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 and limit values will be independent.

      The new buffer's capacity, limit, and position values will be identical to those of this buffer, and its byte order will be BIG_ENDIAN.

      Returns:
      The new, read-only byte 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 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
      Throws:
      ReadOnlyBufferException - If this buffer is read-only

    • slice

      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, and limit 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 byte order will be BIG_ENDIAN. 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.

      Specified by:
      slice in class Buffer
      Returns:
      The new byte buffer