Reading data from a file with the name supplied by the user:
import java.awt.*;
// Need this import for reading data:
import java.io.*;
import java.util.*;
// reading data in a Java application
public class FileReadTest {
public static void main (String [] args) throws IOException {
// read the file name from standard input
BufferedReader nameinput = new BufferedReader(
new InputStreamReader(System.in));
System.out.println("Please enter a file name: ");
String filename = nameinput.readLine();
BufferedReader in;
// open the file for writing:
PrintWriter out = new PrintWriter(new BufferedWriter(
new FileWriter("out.txt")));
// get timestamp:
Date tstamp = Calendar.getInstance().getTime();
out.println(tstamp.getHours() + ":" + tstamp.getMinutes() +
":" + tstamp.getSeconds());
int n = 0; // need to initialize
try {
in = new BufferedReader(
new FileReader(filename));
// read a line of input
// must use "in" within the "try" because it
// may be undefined outside
String line;
line = in.readLine();
// check what the input is:
out.println("The input is: " + line);
// extract the integer from the entered data:
n = Integer.parseInt(line);
// print out the value of n:
in.close();
} catch (IOException e) {
System.out.println("There was a problem opening the file " +
filename);
System.out.println(e.getMessage());
System.exit(0);
}
// output n:
out.println("n = " + n);
// increment n by 1
n = n + 1;
// print out the result:
out.println("n = " + n);
out.close();
}
}
This is an example from CSci 1211 course.