1. CSC1401 Input and Output (with Files)

2. Learning Goals Computing concepts Input and output with files in Java
Using the Scanner class for file input, and PrintWriter for output

3. Recall … import java.util.*; // needed for scanner class IOTesting {
public static void main(String [] args)
{ Scanner scan = new Scanner(System.in); int value = scan.nextInt(); …

4. Using Files for input Instead of System.in, we can specify a file
Two differences
We need to import java.io.*;
Doing file input can lead to an exception if the type of data we are requesting doesn’t match what’s in the file

5. Note the changes import java.util.*; // needed for scanner
import java.io.*; // needed for file
class FileIO {
public static void main(String [] args) throws Exception
// throws exception is for file i/o
{ Scanner sc = new Scanner(System.in); Scanner sc2 = new Scanner(new File("data.txt")); int i = sc2.nextInt(); …

6. Let’s create a file and try
Can use Notepad, or just about anything else besides MS Word
Let’s read in a bunch of scores into an array

7. Reading several numbers from a file
Scanner sc2 = new Scanner(new File("data.txt")); int [] list = new int[10]; int count = 0;
while (sc2.hasNextInt() && count < 10) { list[count] = sc2.nextInt(); count = count +1; } for (int i = 0; i< count;i++) {
System.out.println("list[“ +
i + "] = “ + list[i]); }
sc2.close(); // when you open a file, you // should close it

8. File Output
Again, we’ll change from System.out to something else

9. An example with file output
import java.io.*; // needed for file
class IO
{ public static void main(String [] args)
throws Exception // throws exception is for file i/o { int i = 5; PrintWriter steveout = new PrintWriter(
new FileWriter("silly2.txt")); steveout.println(i+ " is the value"); steveout.close(); …

10. Summary
We use Printwriter for output to a file (the Media Computation book has an alternate approach)
We use a Scanner object for getting input from a file

11. Reading Assignment
Media Computation Chapter 12, Section 3 (but not section )