Character Input and Output in Java

Character Input and Output in Java
Intermediate Topics

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Background

Raw I/O:
- A way to read bytes from a stream
The Limitations:
- Converting from bytes to characters is complicated because of the different encoding schemes

Motivation

Character-Based I/O:
- Reader and Writer classes that can be used to decorate InputStream and OutputStream objects
Providing Additional Functionality:
- Use the decorator pattern again (however, since there is no interface at the top, each decorator both extends its parent and delegates important operations to its parent)

Some Classes for Character-Based Output

Some Classes for Character-Based Input

One Way to Use Readers

Get an InputStream

System.in
From a File (by constructing a FileInputStream )
From a URL (using the openStream method)
From a Socket (using the getInputStream method)

Create an InputStreamReader (from the InputStream )
Create a BufferedReader (from the InputStreamReader )

One Way to Use Writers

Get an OutputStream

System.out
From a File (by constructing a FileOutputStream )
From a Socket (using the getOutputStream method)

Create an OutputStreamWriter (from the OutputStream )
Create a PrintWriter (from the OutputStreamWriter )

A Simple Example

javaexamples/iobasics/WriterReaderExample.java

The Benefits of Decorating Streams

An Example

javaexamples/iobasics/ReaderExample.java

Processing Text Output

The Approach You've Probably Seen:
- The Concept - Provide formatting information to the output method
- The Participants - The printf() method in the PrintWriter class
Another Approach:
- The Concept - Provide formatted String objects to the output method
- The Participants - NumberFormat , ChoiceFormat , the format() method in

Processing Text Output (cont.)

An Example that Formats "Choices"

javaexamples/iobasics/ChoiceFormatExample.java

Processing Text Output (cont.)

Internationalization:
- Numbers, dates, currencies, etc... are often formatted diffferently in different countries
The Locale Class:
- An encpasulation of a geographical, political or cultural region that can be used for locale-sensitive tasks
International Standards:
- ISO Language Codes
- ISO Country Code

Processing Text Output (cont.)

An Example that Formats Numbers

javaexamples/iobasics/NumberFormatExample.java

Processing Text Input

An Approach You've Seen:
- Use a Scanner object and its next___() methods
Shortcomings of this Approach:
- "Unexpected" consumption (or lack thereof) of newline characters
- Not robust with respect to formatting defects

Processing Text Input (cont.)

A More Robust Approach:
- Only read String objects
- Break the String into parts and convert the parts
Some Relevant Classes/Methods:
- The split() method in the String class and the StringTokenizer class
- Double.parseDouble(java.lang.String) and Integer.parseInt(java.lang.String)

Processing Input (cont.)

Using the StringTokenizer

javaexamples/iobasics/FacultyRecordTokenizer.java

Processing Input (cont.)

Using the parse___() Methods

javaexamples/iobasics/ExpressionTokenizer.java

Processing Input (cont.)

Similarities of String.split() and StringTokenizer:
- Tokenize a String
Differences between String.split() and StringTokenizer:
- split() uses regular expressions, StringTokenizer uses a list of delimiters
- split() returns an array, StringTokenizer is an iterator
- StringTokenizer can return the delimiters as tokens

Processing Input (cont.)

A Comparison of StringTokenizer and String.split()

javaexamples/iobasics/BufferedReaderExample.java

There's Always More to Learn