Streams Cheat Sheet

Readers

Creating readers for different streams.

There are several ways to create Readers:

For a file:

        FileReader reader = new FileReader("filename");

For the terminal:

        InputStreamReader reader = new InputStreamReader(System.in);

For a url:

        URL url = new URL("http://www.cs.williams.edu/~index.html");
        InputStreamReader reader = new InputStreamReader(url.openStream());

For a Socket:

        InputStreamReader reader = new InputStreamReader(socket.getInputStream());

Reading from streams.

All readers allow you to read one character at a time with the read() method.

    int ch = reader.read();

The variable ch is set to a character value between 0 and 255, or -1 when there are no more characters left in the stream (i.e., at the end of a file).

To read whole lines at a time, use a BufferedReader:

    BufferedReader buffer = new BufferedReader(reader);

The reader variable is any reader made above. The following example shows how to read all lines in a file using a buffered reader:

    String s;
    BufferedReader buffer = new BufferedReader(new FileReader("filename"));
    s = buffer.readLine();
    while (s != null) {
        System.out.println(s);
        s = buffer.readLine();
    }

The method readLine() returns null when the reader reaches the end of the stream.

Closing readers.

To close a reader, call the close() method:

    reader.close();

Writers

Creating writers for different streams.

There are several ways to create Writers. We always want to create a PrintWriter for our writer so that we can write more than one character at a time:

For a file:

        PrintWriter writer = new PrintWriter(new FileWriter("filename"));

For the terminal: System.out is already a PrintWriter.
For a Socket:
```
        PrintWriter writer = 
           new PrintWriter(new OutputStreamWriter(socket.getOutputStream()), true);
    
```
For sockets, we need to use one extra parameter for the PrintWriter constructor to indicate that Java should treat the PrintWriter as something that writes to a network.

Writing to streams.

You use a PrintWriter just as we have been using System.out all semester:

    writer.println("some text");
    writer.print("some text");

Unlike println, the print method does not start a new line after printing the text.

Closing writers.

Close writers just like readers:

    writer.close();