For console input, use a Scanner object

• Example:

    Scanner stdin = new Scanner(System.in);

• System.in = an InputStream object predefined in java.lang

• Read one line at a time

  String inputLine = stdin.nextLine();
  

• Convert input

  char   c = inputLine.charAt(0);
  int    i = Integer.parseInt(inputLine);
  long   l = Long.parseLong(inputLine);
  float  f = Float.parseFloat(inputLine);
  double d = Double.parseDouble(inputLine);
  

• Read part of a line: next, nextInt, nextDouble, etc.

• Test for input: hasNext, hasNextInt, etc.

For console output, use System.out

• System.out = a PrintStream object predefined in java.lang

• Useful methods

  print
  println
  

• Can use with primitive data types, Strings, and any object (override the toString method to obtain desired format)

For file input, use a Scanner object

• Example:

  File srcFile = new File("myFile.txt");
  Scanner fileIn = new Scanner(srcFile);

  Throws FileNotFoundException (a checked exception)

• Useful methods

  hasNext, hasNextInt, etc.
  next, nextInt, nextLine, etc.
  close
  

For file output, use a PrintStream object

• Example:

  File dstFile = new File("myFile.txt");
  PrintStream outFile = new PrintStream(dstFile);
  

• Options

  new PrintStream(File file) 
  new PrintStream(String fileName)

  Note: the options above
  • have no automatic line flushing
  • will overwrite a file if it already exists
  • throw FileNotFoundException

• Useful methods

  print
  println
  close
  

• Can use with primitive data types, Strings, and any object (override the toString method to obtain desired format)

See PlanetIO.java for an example of file and console I/O