1. File Input / Output

2. Files Persistent storage So your application can ‘remember’
Similar methods to reading / displaying information as before, but a different ‘destination’

3. Scanner Class Before, we read data from ‘standard input’
Scanner myScanner = new Scanner (System.in);
System.in will read from the keyboard
We can pass Scanner other Objects to read from other sources…

4. Scanner Class Now we use the FileReader class
Don’t forget your imports
java.util
java.io
Scanner myScanner = new Scanner (new FileReader(“c:\\myfolder\\myFile.txt”);

5. FileReader
Scanner myScanner = new Scanner (new FileReader(“c:\\myfolder\\myFile.txt”);
Some Things to notice:
We create a FileReader Object “on the fly”
It doesn’t even have a name
The double slashes
Slash is the escape character
Paths
Relative vs. Absolute
Drive letters

6. FileReader Now we can use the same scanner methods nextInt( )
nextDouble( )
hasNext( )

7. Example
Scanner myScanner = new Scanner (new FileReader(“c:\\myFile.txt”)); String firstName, lastName; double hoursWorked, payRate, wages; firstName = myScanner.next( ); lastName = myScanner.next( ); hoursWorked = myScanner.nextDouble( ); payRate = myScanner.nextDouble( ); wages = hoursWorked * payRate; myScanner.close( );

8. Writing to Files Lots of different “Writer and Reader” classes.
PrintWriter is a good, high level class for reading general data from a file

9. Writing to Files PrintWriter myPW = new PrintWriter(“c:\\myFile.out”);
Can use the familiar output methods on the file
print( )
println( )
myPW.println(“The pay is: $” + pay);
This stores the text in the file “myFile.out”

10. Closing Files Don’t forget to close your files! Saves memory and…
“Flushes the buffer”

11. Files What happens if something goes wrong?
Trying to read a file that isn’t there…
Trying to write to a location that doesn’t exist…
Like the ‘Z:’ drive
Trying to write to a file that is already there…
By default, it overwrites the file.
This may not be what you want!

12. Files
If something goes wrong, the statement that causes a problem throws an exception
One of two things must happen in a method that causes an exception
You deal with it
Or… pass the problem up to the calling method

13. Exceptions
For now, we will ‘pass the buck’ and let the system deal with the potential error
public static void main (String [] args) throws FileNotFoundException {
. . .
// no try – catch block in here }

14. Files
In the real-world, files are useful, but many real world data tasks are handled via a database
mySQL
Websites use a database to hold
Products
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