Java in a Nutshell, 5th Edition

Input/Output with java.io

The java.io package defines a large number of classes for reading and writing streaming, or sequential, data. The InputStream and OutputStream classes are for reading and writing streams of bytes while the Reader and Writer classes are for reading and writing streams of characters. Streams can be nested, meaning you might read characters from a FilterReader object that reads and processes characters from an underlying Reader stream. This underlying Reader stream might read bytes from an InputStream and convert them to characters.

Reading Console Input

You can perform a number of common operations with streams. One is to read lines of input the user types at the console:

import java.io.*;

BufferedReader console = new BufferedReader(new InputStreamReader(System.in));
System.out.print("What is your name: ");
String name = null;
try { 
  name = console.readLine(); 
} 
catch (IOException e) { name = "<" + e + ">"; }  // This should never happen
System.out.println("Hello " + name);

Reading Lines from a Text File

Reading lines of text from a file is a similar operation. The following code reads an entire text file and quits when it reaches the end:

String filename = System.getProperty("user.home") + File.separator + ".cshrc"; try { BufferedReader in = new BufferedReader(new FileReader(filename)); String line; while((line = in.readLine()) != null) { // Read line, check for end-of-file System.out.println(line); // Print the line } in.close(); // Always close ...