FileInputStream vs FileReader

Question

FileReader rd=new FileReader("new.mp4"); FileWriter wr=new FileWriter("output.mp4"); int ch; while((ch=rd.read())!=-1)   wr.write(ch);  wr.flush(); wr.close(); 

When I use the FileReader and FileWriter to read and write an mp4 file, the output.mp4 file can't be rendered well. But when I use FileInputStream and FileOutputStream instead it worked well.

So can I conclude FileReader and FileWriter are only for reading and writing text?

Answer 1

Yes, your conclusion is correct subclasses of Reader and Writer are for reading/writing text content. InputStream / OutputStream are for binary content. If you take a look at the documentation:

Reader - Abstract class for reading character streams

InputStream - Abstract class is the superclass of all classes representing an input stream of bytes.

Answer 2

FileReader (and indeed anything extending Reader) is indeed for text. From the documentation of Reader:

Abstract class for reading character streams.

(Emphasis mine.) Look at the API and you'll see it's all to do with text - char instead of byte all over the place.

InputStream and OutputStream are for binary data, such as mp4 files.

Personally I would avoid FileReader altogether though, as it always uses the system default character encoding - at least before Java 11. Instead, use InputStreamReader around a FileInputStream... but only when you want to deal with text. (Alternatively, use Files.newBufferedReader.)

As an aside, that's a very inefficient way of copying from an input to an output... use the overloads of read and write which read into or write from a buffer - either a byte[] or a char[]. Otherwise you're calling read and write for every single byte/character in the file.

You should also close IO streams in finally blocks so they're closed even if an exception is thrown while you're processing them.