cs1302_lab_06.docx - CS 1302 u2013 Lab 06 This lab...

CS 1302 – Lab 06
This lab provides an introduction to reading and writing text files. There are 6 stages to complete this lab:
Stage Title Text Reference
1 Reading Simply Formatted Data from a Text File 12.11
2 Parsing Data 12.11
3 More Parsing 12.11
4 Writing Data to a Text File 12.11
5 The File Class 12.10
6 Reading & Writing Example 12.11
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Stage 1 - Reading Simply Formatted Data from a Text File
In this stage you will learn how to read an arbitrary number of items with a repetitive pattern from a text file.
1. Read (no action required) –
a. A text file is actually a file filled with binary digits, 1’s and 0’s (which
itself is an abstraction). However, the software (Word, Eclipse, etc. )
that accesses a text file uses character decoding. For example, the
binary stream:
01001010011000010111011001100001
Is decoded (each 8 bits) as:
8-bit Blocks 0100101
0
0110000
1
0111011
0
0110000
1
Decoded ASCII Text J a v a
b. The encoding/decoding scheme shown on the right is ASCII . For example the (partial) table above on the
right shows how text is encoded/decoded. For example, the ASCII letter “a” is represented in binary as:
01100001. ASCII was the standard on the internet until 2007. Now, UTF-8 is the standard. UTF-8 was
designed to be backwards compatible with ASCII, so they are the same. Be default, Java reads and writes
using ASCII, however you can set a parameter to use UTF-8.
c. The information above is not directly needed for this course but is useful for a general understanding.
Usually (and always for this course) when we read/write information to/from a text file the
decoding/encoding is done automatically.
1
ASCII Dec Hex Binary
0 48 30 0011 0000
1 49 31 0011 0001
2 50 32 0011 0010
… … … …
A 65 41 0100 0001
B 66 42 0100 0010
C 67 43 0100 0011
… … … …
a 97 61 0110 0001
b 98 62 0110 0010
c 99 63 0110 0011
… … … …

2. Read (no action required) –
a. Consider a text file with the data shown on the right. The line numbers (1-15) are shown
on the left and are not a part of the file. Each three lines represents an employee
name, salary, age .
b. To read (or write) data we first create an instance of the File class which contains the
location of the file. Later in this tutorial we will look more closely at the File class. For
now, we will just see how to create an instance. The File class constructor accepts a path
with the location and name of the file. For example:
File inFile = new File( "src\\examples1\\employees1.txt"
specifies that the file is named employee1.txt and it is found in the src\examples1 folder.
An additional “\” is needed to delimit the single, required “\” in the path. Notice that
this is a relative path. Eclipse is configured to look for a file in the src folder by default
and since we will typically have our code in a package ( example1 in the example above)
we need to specify the full path.
c. We use the Scanner class in Java to read from a text file (just as you did to read from the keyboard) passing
into its constructor a File object.
Scanner input = new Scanner( inFile
d.
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