1. Input and Output in Java
Thursday, Jan 20, 2011
Nancy L. Harris

2. Reference for this topic
Java Tutorials I/O
CS239 – Spring
1/18/2006

3. Pictorial view of data streams (from the Java tutorial)

4. What can we read and write?
Bytes – used for binary data, sounds, pictures
Characters – used for textual data
We will focus on character data
1/20/2011
CS239 – Spring

5. What does a “stream” look like
It is not organized as we are used to looking at a “file”.
It is conceptually an infinitely long series of bytes.
Some readers deal with those bytes as text characters.
And each format item (new lines, tabs, spaces) have a corresponding character representation.
CS239 – Spring 2011
1/20/2011

6. What’s a file?
A “file” can be thought of as a named bunch of sequential data.
That data can be binary (like executable programs) or it can be textual (like the source files you make with JGrasp).
Text files are still binary, but their data can be directly interpreted as characters from the Unicode character set.
1/20/2011
CS239 – Spring

7. Processing a file To read from a file To write to a file Open the file
Read its data
Close the file
To write to a file
Write its data
1/20/2011
CS239 – Spring

8. Java supports Input File class Scanner class Output Printwriter class
CS239 – Spring
1/20/2011

9. Making a copy of a file
Involves reading from a source and writing to a target. Demo
Note: File I/O requires the handling of “checked” exceptions.
These exceptions must be handled or re-thrown.
1/20/2011
CS239 – Spring

10. A note about whitespace
Scanner automatically uses “whitespace” to parse input.
We can force it to use something else by the useDelimiter() method.
Scanner can process:
standard input (System.in)
files
lines of text
It’s process of reading individual elements is also called parsing or tokenizing.
CS239 – Spring
1/20/2011

11. StringTokenizer
Class which is also designed to parse a String of data (like a line of text).
It can use different delimiters. We then need to use parseInt or parseDouble to make sense of numeric data.
CS239 – Spring
1/20/2011