I am trying to read a text file, and then display the output in another file. I can only read using Scanner. input.txt

3005045 7
3245436 0
7543536 3
8684383 -1

output.txt should be like

ID    Number of Bags   Total Cost
**    **************   **********

customer pays 20.50 per bag if the bag is 4 or less. and pays 15.50 per bag if the bag greater than 4. but if it's 0 or negative number this message should appeared "Error : Wrong Number of Bags" I did this program, but it works only once(reads one line only)

import java.util.*;
import java.io.*;
import java.io.IOException;

public class Bags {
public static void main(String []args) throws IOException {
    FileInputStream fileinput = new FileInputStream("input.txt");
    FileOutputStream fileoutput = new FileOutputStream("output.txt");
    Scanner infile = new Scanner(fileinput);
    PrintWriter pw = new PrintWriter(fileoutput);
    double total = 0, line = 0;
    int bags = 0, ID = 0, count = 0;
    pw.println("ID\t\tNumber of Bags\t\t\tTotal Cost");
    for(int i = bags; i >= 0; i++, count++){
        ID = infile.nextInt();
        i = infile.nextInt();
        if (i <= 0){
            pw.println(ID + "\tError: Wrong Number of Bags\t\t\t");
            break;
        }
        else if (i <= 4){
            total = (80.50)*i;
            pw.printf("%d\t\t%d\t\t\t\t%.2f", ID, i, total);
            break;
        }
        else {
            total = ((80.50)*4)+((75.50)*(i-4));
            pw.printf("%d\t\t%d\t\t\t\t%.2f", ID, i, total);
            break;
        }
    }
    infile.close();
    pw.close();
}
}

You don't need that for loop over there. Also, you want to read line by line. Here is quick fix of your code:

public class Bags {

public static void main(String[] args) throws IOException {
    FileInputStream fileinput = new FileInputStream("input.txt");
    FileOutputStream fileoutput = new FileOutputStream("output.txt");
    Scanner infile = new Scanner(fileinput);
    PrintWriter pw = new PrintWriter(fileoutput);
    double total = 0, line = 0;
    int bags = 0, ID = 0, count = 0;
    pw.println("ID\t\tNumber of Bags\t\t\tTotal Cost");
    while(infile.hasNext()){

        ID = infile.nextInt();
        int i = infile.nextInt();
        if (i <= 0) {
            pw.println(ID + "\n\t\tError: Wrong Number of Bags\t\t\t");

        } else if (i <= 4) {
            total = (80.50) * i;
            pw.printf("%d\t\t%d\t\t\t\t%.2f", ID, i, total);

        } else {
            total = ((80.50) * 4) + ((75.50) * (i - 4));
            pw.printf("%d\t\t%d\t\t\t\t%.2f", ID, i, total);

        }
    }
    infile.close();
    pw.close();
}
}

Output.txt

ID      Number of Bags                  Total Cost
3005045 7                               548.503245436
        Error: Wrong Number of Bags
7543536 3                               241.508684383
        Error: Wrong Number of Bags

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