What is the use of ByteBuffer in Java

Question

What are example applications for a ByteBuffer in Java  Please list any example scenarios where this is used  Thank you

User · Answer

Java IO using stream oriented APIs is performed using a buffer as temporary storage of data within user space. Data read from disk by DMA is first copied to buffers in kernel space, which is then transfer to buffer in user space. Hence there is overhead. Avoiding it can achieve considerable gain in performance.

We could skip this temporary buffer in user space, if there was a way directly to access the buffer in kernel space. Java NIO provides a way to do so.

ByteBuffer is among several buffers provided by Java NIO. Its just a container or holding tank to read data from or write data to. Above behavior is achieved by allocating a direct buffer using allocateDirect() API on Buffer.

Java Documentation of Byte Buffer has useful information.

User · Answer

This is a good description of its uses and shortcomings  You essentially use it whenever you need to do fast low-level I O  If you were going to implement a TCP IP protocol or if you were writing a database  DBMS  this class would come in handy

User · Answer

Here is a great article explaining ByteBuffer benefits  Following are the key points in the article    First advantage of a ByteBuffer irrespective of whether it is direct or indirect is efficient random access of structured binary data  e g   low-level IO as stated in one of the answers   Prior to Java 1 4  to read such data one could use a DataInputStream  but without random access    Following are benefits specifically for direct ByteBuffer MappedByteBuffer  Note that direct buffers are created outside of heap    Unaffected by gc cycles  Direct buffers won t be moved during garbage collection cycles as they reside outside of heap  TerraCota s BigMemory caching technology seems to rely heavily on this advantage  If they were on heap  it would slow down gc pause times  Performance boost  In stream IO  read calls would entail system calls  which require a context-switch between user to kernel mode and vice versa  which would be costly especially if file is being accessed constantly  However  with memory-mapping this context-switching is reduced as data is more likely to be found in memory  MappedByteBuffer   If data is available in memory  it is accessed directly without invoking OS  i e   no context-switching     Note that MappedByteBuffers are very useful especially if the files are big and few groups of blocks are accessed more frequently    Page sharing  Memory mapped files can be shared between processes as they are allocated in process s virtual memory space and can be shared across processes

User · Answer

The ByteBuffer class is important because it forms a basis for the use of channels in Java  ByteBuffer class defines six categories of operations upon byte buffers  as stated in the Java 7 documentation         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       Example code   Putting Bytes into a buffer          Create an empty ByteBuffer with a 10 byte capacity     ByteBuffer bbuf   ByteBuffer allocate 10           Get the buffer s capacity     int capacity   bbuf capacity       10         Use the absolute put int  byte          This method does not affect the position      bbuf put 0   byte 0xFF      position 0         Set the position     bbuf position 5           Use the relative put byte      bbuf put  byte 0xFF           Get the new position     int pos   bbuf position       6         Get remaining byte count     int rem   bbuf remaining       4         Set the limit     bbuf limit 7      remaining 1         This convenience method sets the position to 0     bbuf rewind       remaining 7

User · Answer

In Android you can create shared buffer between C   and Java  with directAlloc method  and manipulate it in both sides

[java] What is the use of ByteBuffer in Java?

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