Java difference between FileWriter and BufferedWriter

Question

What s the difference between those  I m just learning Java ATM  but it seems like I can write to a file both ways i e   I didn t copy the try-catch block here    FileWriter file   new FileWriter  foo txt    file write  foobar    file close      and  FileWriter file   new FileWriter  foo txt    BufferedWriter bf   new BufferedWriter file   bf write  foobar    bf close      I understand the concept of buffering the data first  so does that mean the first example writes the characters one by one and the second first buffers it to the memory and writes it once

User · Answer

http   docs oracle com javase 1 5 0 docs api java io BufferedWriter html     In general  a Writer sends its output immediately to the underlying character or byte stream  Unless prompt output is required  it is advisable to wrap a BufferedWriter around any Writer whose write   operations may be costly  such as FileWriters and OutputStreamWriters  For example       PrintWriter out        new PrintWriter new BufferedWriter new FileWriter  foo out           will buffer the PrintWriter s output to the file  Without buffering  each invocation of a print   method would cause characters to be converted into bytes that would then be written immediately to the file  which can be very inefficient

User · Answer

BufferedWriter is more efficient  It saves up small writes and writes in one larger chunk if memory serves me correctly  If you are doing lots of small writes then I would use BufferedWriter  Calling write calls to the OS which is slow so having as few writes as possible is usually desirable

User · Answer

From the Java API specification   FileWriter     Convenience class for writing character files  The constructors of this class assume that the default character encoding and the default byte-buffer size are acceptable    BufferedWriter     Write text to a character-output stream  buffering characters so as to provide for the efficient writing of single characters  arrays  and strings

User · Answer

In unbuffered Input Output FileWriter  FileReader  read or write request is handled directly by the underlying OS  https   hajsoftutorial com java wp-content uploads 2018 04 Unbuffered gif  This can make a program much less efficient  since each such request often triggers disk access  network activity  or some other operation that is relatively expensive  To reduce this kind of overhead  the Java platform implements buffered I O streams  The BufferedReader and BufferedWriter classes provide internal character buffers  Text that   s written to a buffered writer is stored in the internal buffer and only written to the underlying writer when the buffer fills up or is flushed  https   hajsoftutorial com java wp-content uploads 2018 04 bufferedoutput gif  More https   hajsoftutorial com java-bufferedwriter

User · Answer

You are right  Here is how write   method of BufferedWriter looks   public void write int c  throws IOException       synchronized  lock            ensureOpen            if  nextChar  gt   nChars              flushBuffer            cb nextChar       char  c            As you can see it indeed checks whether the buffer is full  if  nextChar  gt   nChars   and flushes the buffer  Then it adds new character to buffer  cb nextChar       char  c

User · Answer

BufferedWriter is more efficient if you   have multiple writes between flush close the writes are small compared with the buffer size    In your example  you have only one write  so the BufferedWriter just add overhead you don t need      so does that mean the first example writes the characters one by one and the second first buffers it to the memory and writes it once   In both cases  the string is written at once   If you use just FileWriter your write String  calls   public void write String str  int off  int len              some code         str getChars off   off   len   cbuf  0           write cbuf  0  len        This makes one system call  per call to write String      Where BufferedWriter improves efficiency is in multiple small writes   for int i   0  i  lt  100  i          writer write  foorbar        writer write NEW LINE     writer close      Without a BufferedWriter this could make 200  2   100  system calls and writes to disk which is inefficient  With a BufferedWriter  these can all be buffered together and as the default buffer size is 8192 characters this become just 1 system call to write

[java] Java difference between FileWriter and BufferedWriter

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