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Android Android Data Persistence File Storage Writing to Internal Storage

In the copyFile() method, why use a while loop?

In the copyFile() method, the write() method is writing "read" number of bytes to "buffer". If this step occurs as a single step, why use a while loop?


private static void copyFile(InputStream in, OutputStream out) {

byte[] buffer = new byte[1024];

int read;


out.write(buffer, 0, read);



1 Answer

David Petersheim
David Petersheim
8,366 Points

A while loop is used because it may take more than one read to get all of the bytes transferred. This could be caused by one of two things.

Either the buffer is smaller than the file

If the buffer is smaller than the file, say a 10-byte buffer and a 40-byte file, then it will take at least 4 reads to get all 40 bytes from the file.

Or the read method doesn't read the whole file at once

The read method returns an integer that tells the caller how many bytes were read from the stream. If -1 is returned then the stream has ended.

The test in the while loop checks for -1. If -1 is returned, then the job is over. If another number is returned, then that number of bytes is written to the output stream.

The code is using a 1024-byte buffer. If

James O'Kelly
James O'Kelly
12,790 Points

It is true that it may take more that one read, but it should increment the offset (which is currently always 0) in the output buffer by the amount of bytes read, because it currently would overwrite the buffer each time around the loop as it currently stands.