Java IO and C++ Streams

Transcription

1 Java IO and C++ Streams October 22, 2004 Operator Overloading in C p. 1/31

2 Outline Java IO InputStream/OutputStream FilterInputStream/FilterOutputStream DataInputStream/DataOutputStream Reader/Writer Encodings C++ Streams Operator Overloading in C p. 2/31

3 java.io - Intro Two main abstractions: streams of bytes InputStream abstract class is the superclass of all classes representing an input stream of bytes OutputStream abstract class is the superclass of all classes representing an output stream of bytes streams of characters Operator Overloading in C p. 3/31

4 java.io - Intro Two main abstractions: streams of bytes streams of characters Reader abstract class is the superclass of all classes representing an input stream of characters Writer abstract class is the superclass of all classes representing an output stream of characters Operator Overloading in C p. 4/31

5 OutputStream must always provide at least a method that writes one byte of output methods: void close() void flush() void write(byte[] b) void write(byte[] b, int off, int len) abstract void write(int b) subclasses Operator Overloading in C p. 5/31

6 OutputStream (cont) subclasses: ByteArrayOutputStream data is written into a byte array the buffer automatically grows as data is written to it FileOutputStream writing data to a File or to a FileDescriptor meant for writing streams of raw byte FilterOutputStream ObjectOutputStream PipedOutputStream Operator Overloading in C p. 6/31

7 OutputStream (cont) subclasses: ByteArrayOutputStream FileOutputStream FilterOutputStream superclass of all classes that filter output streams subclasses: BufferedOutputStream, CheckedOutputStream, CipherOutputStream, DataOutputStream, DeflaterOutputStream, DigestOutputStream, PrintStream ObjectOutputStream PipedOutputStream Operator Overloading in C p. 7/31

8 OutputStream (cont) subclasses: ByteArrayOutputStream FileOutputStream FilterOutputStream ObjectOutputStream writes primitive data types and graphs of Java objects only objects that support the java.io.serializable interface can be written to streams primitive data types can also be written PipedOutputStream can be connected to a piped input stream to create a communications pipe Operator Overloading in C p. 8/31

9 FilterOutputStream writes data to another OutputStream two kind of subclasses: processing of the data: BufferedOutputStream CheckedOutputStream CipherOutputStream DeflaterOutputStream GZIPOutputStream ZipOutputStream DigestOutputStream provides an expanded interface: DataOutputStream PrintStream: polymorphic print and println, printf Operator Overloading in C p. 9/31

10 DataOutputStream Extended interface provided by DataOutputStream: void writeboolean(boolean v) void writebyte(int v) void writebytes(string s) void writechar(int v) void writechars(string s) void writedouble(double v) void writefloat(float v) void writeint(int v) void writelong(long v) void writeshort(int v) void writeutf(string str) Operator Overloading in C p. 10/31

11 OutputStream - Example FileOutputStream fileout = new FileOutputStream("myfile"); // add buffering BufferedOutputStream bufout = new BufferedOutputStream(fileOut); // add compression GZIPOutputStream gzout = new GZIPOutputStream(bufOut); // interface for binary data DataOutputStream out = new DataOutputStream(gzOut); // some writing out.writeint(n); out.writedouble(d); Operator Overloading in C p. 11/31

12 OutputStream - What if? FileOutputStream fileout = new FileOutputStream("myfile"); BufferedOutputStream bufout = new BufferedOutputStream(fileOut); GZIPOutputStream gzout = new GZIPOutputStream(bufOut); DataOutputStream out1 = new DataOutputStream(gzOut); DataOutputStream out2 = new DataOutputStream(bufOut); out1.writeint(n); out2.writedouble(d); Operator Overloading in C p. 12/31

13 OutputStream - What if? FileOutputStream fileout = new FileOutputStream("myfile"); BufferedOutputStream bufout = new BufferedOutputStream(fileOut); GZIPOutputStream gzout = new GZIPOutputStream(bufOut); DataOutputStream out1 = new DataOutputStream(gzOut); DataOutputStream out2 = new DataOutputStream(bufOut); out1.writeint(n); out2.writedouble(d); The output will be corrupted! Operator Overloading in C p. 13/31

14 OutputStream - A common construction DataOutputStream out = new DataOutputStream( new GZIPOutputStream( new BufferedOutputStream( FileOutputStream("myfile")))); out.writeint(n); out.writedouble(d); Operator Overloading in C p. 14/31

15 InputStream similar with OutputStream but in reverse subclasses: ByteArrayInputStream FileInputStream FilterInputStream ObjectInputStream PipedInputStream SequenceInputStream represents the logical concatenation of other input streams Operator Overloading in C p. 15/31

16 The other world: characters Writer methods that a subclass must implement are: write(char[], int, int), flush(), and close() subclasses: BufferedWriter, CharArrayWriter, FilterWriter, OutputStreamWriter, FileWriter, PipedWriter, PrintWriter, StringWriter Reader methods that a subclass must implement are read(char[], int, int) and close() subclasses: BufferedReader, CharArrayReader, FilterReader, InputStreamReader, PipedReader, StringReader What is the big difference? Operator Overloading in C p. 16/31

17 The other world: characters Writer methods that a subclass must implement are: write(char[], int, int), flush(), and close() subclasses: BufferedWriter, CharArrayWriter, FilterWriter, OutputStreamWriter, FileWriter, PipedWriter, PrintWriter, StringWriter Reader methods that a subclass must implement are read(char[], int, int) and close() subclasses: BufferedReader, CharArrayReader, FilterReader, InputStreamReader, PipedReader, StringReader What is the big difference? Encodings! Operator Overloading in C p. 17/31

18 InputStreamReader/OutputStreamWriter InputStreamReader is a bridge from byte streams to character streams reads bytes and decodes them into characters using a specified charset OutputStreamWriter the opposite of InputStreamReader Operator Overloading in C p. 18/31

19 Encodings JDKTM 5.0 Documentation Tool Docs Internationalization Tools native2ascii Supported Encodings docs/guide/intl/encoding.doc.html Operator Overloading in C p. 19/31

20 Another Universe: C++ Streams Operator Overloading in C p. 20/31

21 Reference The C++ Programming Language, Third Edition by Bjarne Stroustrup. Published by Addison Wesley Longman, Inc. Operator Overloading in C p. 21/31

22 Standard Streams Several standard streams are declared in <iostream>: ostream cout // standard output stream // of char ostream cerr // standard unbuffered output // stream for error messages ostream clog // standard output stream for // error messages wostream wcout; // wide stream ver. of cout wostream wcerr; // wide stream ver. of cerr wostream wclog; // wide stream ver. of clog Operator Overloading in C p. 22/31

23 istream Provides:» get getline read gcount putback tie Operator Overloading in C p. 23/31

24 ostream Provides: «put write Operator Overloading in C p. 24/31

25 State bool good() const; // next op. might succeed bool eof() const; // end of input seen bool fail() const; // next op. will fail bool bad() const; // stream is corrupted iostate rdstate() const; // get io state flags void clear(iostate f = goodbit); // set io state flags void setstate(iostate f) { clear(rdstate() f); // add f to iostate flags } operator void*() const; // nonzero if!fail() bool operator!() const { return fail(); } Operator Overloading in C p. 25/31

26 Formating static const fmtflags skipws, // skip whitespace on input left // pad after value right, // pad before value internal, // pad between sign and value boolalpha, // use symbolic representation dec, // base 10 output (decimal) hex, // base 16 output (hexadecimal) oct, // base 8 output (octal) scientific, // d.ddddddedd fixed, // dddd.dd showbase, // prefix oct by 0 and hex by 0x showpoint, // print trailing zeros showpos, // explicit + for positive ints uppercase; // E, X rather than e, x Operator Overloading in C p. 26/31

27 Formating (cont) // read flags fmtflags flags() const; // set flags fmtflags flags(fmtflags f); // add flags fmtflags setf(fmtflags f) { return flags(flags() f); } // clear flags void unsetf(fmtflags mask) { flags(flags()& mask); } Operator Overloading in C p. 27/31

28 Manipulators declared in <iomanip>, namespase std Manipulators: boolalpha, noboolalpha showbase, noshowbase showpoint, noshowpoint showpos, noshowpos skipws, noskipws, ws uppercase, nouppercase internal left, right dec, hex, oct fixed, scientific Operator Overloading in C p. 28/31

29 Manipulators (cont) Manipulators (cont): endl, ends flush resetioflags, setioflags setbase setfill setprecision setw Operator Overloading in C p. 29/31

30 Other kinds of streams File Streams <fstream> ifstream, ofstream, fstream String Streams <sstream> istringstream, ostringstream, stringstream wistringstream, wostringstream, wstringstream Stream Buffers Operator Overloading in C p. 30/31

31 That s all! Have a nice weekend! Operator Overloading in C p. 31/31