Streams and Readers The stream hierarchy is for reading bytes, the - PowerPoint PPT Presentation

Streams and Readers ● The stream hierarchy is for reading bytes, the reader/writer hierarchy is for reading characters ➤ Unicode characters can be used internationally, variety of languages/characters, the future beyond ASCII ➤ bytes are used on most machines for external storage, convenient also for storing raw objects/values, e.g., int stored as 0x000000ff vs “255” ● More than 50 input/output streams readers/writers ➤ many are specialized, good to know that they’re there, but how can you pick which one to use? ➤ Examples: raw, RandomAccess, Buffered, PushBack, Zip, StringBuffer, Object, File, ... 25. 1 Duke CPS 108

Streams ● InputStream get raw bytes from a source ➤ source could be URL, File, Pipe, String, … ➤ one abstract method, must be implemented, returns byte or -1 if no more data, this method blocks public abstract int read() throws IOException ➤ other read methods implemented in terms of read(), e.g., read(byte b[]) and read(byte b[], int offset, int length) ● OutputStream is similar, writes raw bytes ➤ one abstract method, two others similar to InputStream public abstract void write(int b) throws IOException ● Parameters and variables can be bound to concrete implementations of these abstract classes 25. 2 Duke CPS 108

Chaining Streams ● Read doubles, use buffering, from a file DataInputStream input = new DataInputStream( new BufferedInputStream( new FileInputStream(“numbers.dat”))); double d = input.readDouble(); ● What about reading from a gzip’d file, use GZIPInputStream, from java.util.zip ● What about reading from a URL?, use URL class in java.net (URL.openStream()). 25. 3 Duke CPS 108

Readers/Writers for Unicode ● Writing text (as opposed to bytes) can be done with the PrintWriter class ➤ has print(Foo f) method for all built-in types, for String, and for Object ➤ wrapper for other Writer objects and for OutputStreams ● Reading text can be done with a BufferedReader (for line oriented text) ➤ bind the reader to a FileReader or an InputStream of appropriate type ➤ use InputStreamReader as bridge between streams and readers • specify character encoding here, e.g., 8859_7, which is ISO Latin/Arabic 25. 4 Duke CPS 108