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In Java, what is the advantage of using BufferedWriter to append to a file?
The site that I am looking at says
"The BufferWriter class is used to write text to a character-output stream, buffering characters so as to provide for the efficient writing of single characters, arrays, and strings."
What make's it more efficient and why?
BufferedWriter is more efficient because it uses buffers rather than writing character by character. So it reduces I/O operations of the disk. Data is collected in a buffer and write to the file when the buffer is full.
This is why sometimes no data is written in the file if you didn't call flush method. That is data is collected in the buffer but program exits before writing them to the file. Calling flush method will cause the data to be written in the file even the buffer is not filled completely.
The cost of writing becomes expensive when you write character by character to the file. For reducing that cost, buffers are provided. If you are writing to Buffer, it waits for some limit and then writes the whole to the disk.
A BufferedWriter waits until the buffer (8192 bytes) is full and writes the whole buffer in one disk operation. Unbuffered each single write would result in a disk I/O which is obviously more expensive.
As the name suggests, BufferedWriter uses a buffer to reduce the costs of writes. If you are writing to file, you might know that writing 1byte or writing 4kbytes roughly costs the same. The time required to perform such write is dominated by the access time (~8ms) which is the time required by the disk to rotate and to seek the right sector.
Additionally, aggregating small writes in a bigger one allows you to reduce the overhead on the operating system, achieving better performances.
Most of the operating systems do have an internal buffer to cache writes. However, these caches tries to figure out what the application is doing, by analyzing the write patterns. If the application itself is able to perform that caching, and perform a write only when the data is ready, the result (in terms of performance) is better.
Hard disk hava a minimum unit of information storage so for example if you are writing a single byte the operating system asks for the disk to store a unit of storage (I think that the minimum is 512 bytes). So you ask for writing one byte and the operating system writes much more. If you ask to store 512 bytes with 512 calls you end up doing a lot more I/O (512 disk operations) that buffering 512 bytes and issuing only one call (1 disk operation).
