DCO10103 Object-Oriented Programming and Design

java.io.*

classes that your programs can use to read and to write data
- I/O Stream
- to input is to open a stream on an information source (a file, memory, a socket) and read the data (16 bits character or a byte)
- Character Input Streams (public abstract class Reader)
```
java.lang.Object
  |
  +--java.io.Reader
         |
         +--BufferedReader, CharArrayReader, FilterReader, 
            InputStreamReader, PipedReader, StringReader
```
- to output is to open a stream to a destination and write the data
- Character Output Streams (public abstract class Writer)
```
java.lang.Object
  |
  +--java.io.Writer
         |
         +--BufferedWriter, CharArrayWriter, FilterWriter, 
            OutputStreamWriter, PipedWriter, PrintWriter,
            StringWriter
```
- to read and write 8-bit bytes, programs should use the byte streams which are subclass of the abstract InputStream and OutputStream class

input examples

BufferedReader  br;
String  s;

br = new  BufferedReader(new  InputStreamReader(System.in));
s = br.readLine();  // read one line from console

br = new  BufferedReader(new  FileReader("filename"));
s = br.readLine();  // read one line from a file

br = new  BufferedReader(new
       StringReader("This is a string\nwith two lines.");
s = br.readLine();  // read one line from a string
                    // (the string resides in
                    // the StringReader object)

output examples

PrintWriter  pw;
String  s = "A line of text.";

pw = new  PrintWriter(System.out, true);
pw.println(s);  // print one line to console

pw = new  PrintWriter(new  FileWriter("filename"));
pw.println(s);  // print one line to a file

StringWriter  sw;
pw = new  PrintWriter(sw = new  StringWriter());
pw.println(s);  // print one line to a string
                // (the string resides in
                // the StringWriter object)

PrintWriter  pw = new  PrintWriter(sw);
pw.print("Hello");
pw.print(", there!");
pw.flush();
stdOut.println(sw.toString());

The java.io.StreamTokenizer
- is more powerful and general than the java.util.StringTokenizer
- parses streams instead of strings
- each token is automatically converted to either a double, or a String
- the ttype, nval, and sval fields of StreamTokenizer

example

String  s = "12 this that 52.7 hey5"
StreamTokenizer  st = new
 StreamTokenizer(new  StringReader(s));
int  nums = 0, words = 0;

st.nextToken();  // could throw IOException
while (st.ttype != st.TT_EOF)  {
  switch (st.ttype)  {
    case st.TT_NUMBER:
      ++nums;
      break;
    case st.TT_WORD:
      ++words;
      break;
  }
  st.nextToken();  // could throw IOException
}

stdOut.println("In string:  " + s);
stdOut.println("Number of numbers:  " + nums +
                ", number of words:  " + words);

The output follows.

In string:  12 this that 52.7 hey5
Number of numbers:  2, number of words:  3

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