PIC20A - BufferedReader

How to get user input from DOS?

import java.io.*;

public class Input {
    public static void main(String[] args) {
        BufferedReader in = new BufferedReader(
                  new InputStreamReader(System.in));
        String input = null;
        try {
            while((input = in.readLine())!=null) {
                System.out.println("Your input is : " + input );
            }
        } catch (IOException ex) {
            System.out.println("Error in I/O");
            System.exit(-1);
        }
    }
}

Here is a sample output

C:>java Input
Hi
Your input is : Hi
Hello
Your input is : Hello
Who are you?
Your input is : Who are you?

Explanation

BufferedReader in = ..... : creates a BufferedReader from System.in.
in.readLine(): read a line from user input. Returns null if there is no more input.

IOException

The while loop processes the user input.

How to read numbers from file or from user input?

Question: I have a file with a list of doubles in several lines. The doubles are seperated by a comman (,) and then a space. I want to find out the average of the numbers on each line and print out the average.
Here is my file (save as data.txt):

1.5, 3.78, 9.2, 2.4
1.56, 1.56, 1.59, 3.1, 4.5
1.5, 2.9, 1.5, 1.1     
1, 2, 30
5.5, 5.9

Average.java

import java.io.*;

public class Average {
    public static void main(String[] args) {
        BufferedReader in = null;
        String inputFileName = "data.txt";
        try {
            in = new BufferedReader(new FileReader(inputFileName));
        } catch (FileNotFoundException ex) {
            // print out the line number that causes the exception
            ex.printStackTrace(); 
            System.exit(-1); // exit
        }
        
        String line = null; // one line for the file
        String[] data; 
        
        try {
            double sum = 0;
            int num;
            while((line = in.readLine()) != null) {
                data = line.split(", "); // split the line by comma-space
                sum=0;
                num = data.length;
                for(int i = 0; i < num; i++) {
                    sum+=Double.parseDouble(data[i]);
                }
                System.out.println(sum/num);
            }
        } catch (IOException ex) {
            ex.printStackTrace();
            System.exit(-1);
        } 
        
        try {
            in.close();
        } catch (IOException ex) {
        }
    }
}

Output on DOS prompt

4.22
2.462
1.75
11.0
5.7

Explanation

split(String exp) method in String class splits the string by exp.

Another way to write this program is

import java.io.*;

public class Average {
    public static void main(String[] args) {
        BufferedReader in = null;
        String inputFileName = "data.txt";
        try {
            in = new BufferedReader(new FileReader(inputFileName));
        } catch (FileNotFoundException ex) {
            // print out the line number that causes the exception
            ex.printStackTrace(); 
            System.exit(-1); // exit
        }
        
        String line = null; // one line for the file
        String[] data; 
        
        try {
            double sum = 0;
            int num;
            while((line = in.readLine()) != null) {
                data = line.split(","); // split the line by comma
                sum=0;
                num = data.length;
                for(int i = 0; i < num; i++) {
                    sum+=Double.parseDouble(data[i].trim());// trim method remove the white spaces 
                                                             // in front and after the string
                }
                System.out.println(sum/num);
            }
        } catch (IOException ex) {
            ex.printStackTrace();
            System.exit(-1);
        } 
        
        try {
            in.close();
        } catch (IOException ex) {
        }
    }
}