Question

I was trying to read a file.dat that contains many commands which are the character at the front of each line. But somehow the code that I wrote seems to skip or not recognize some of the character at the front of some line.

This is the file(original):

p 10 1 100
p 23 1 50
p 12 2 275
d 1
s 1
p 14 2 1050
d 3
x 4
p 37 2 25
p 41 1 500
d 2
s 2
q

This is the result:

 got p!
 x, y, z of p command are: 10, 1, 100
 got p!
 x, y, z of p command are: 23, 1, 50
 got p!
 x, y, z of p command are: 12, 2, 275
 command not found
 got p!
 x, y, z of p command are: 14, 2, 1050
 command not found
 got p!
 x, y, z of p command are: 37, 2, 25
 got p!
 x, y, z of p command are: 41, 1, 500
 got s
 x of s command is: 2
 java.util.NoSuchElementException
 Process finished with exit code 0

However, the results that came out would bring another error when I tried to edit the file a bit(just swap 2 lines)

Here is the edited file:

d 3
p 10 1 100
p 23 1 50
p 12 2 275
s 1
d 1
p 14 2 1050
x 4
p 37 2 25
p 41 1 500
d 2
s 2
q

The result of the edited file:

command not found
command not found
command not found
got s
x of s command is: 1
command not found
command not found
got p!
x, y, z of p command are: 37, 2, 25
got p!
x, y, z of p command are: 41, 1, 500
got s
x of s command is: 2
java.util.NoSuchElementException
Process finished with exit code 0

And this is the code that I wrote:

import java.io.File;
import java.util.NoSuchElementException;
import java.util.Scanner;

public class test3 {
    public static void main(String[] args) throws Exception {
        File file = new File("file.dat");
        try {
            Scanner input = new Scanner(file);
            while (input.hasNext()) {
                if ("p".equals(input.next())) {
                    System.out.println("got p!");
                    String x = input.next();
                    String y = input.next();
                    String z = input.next();

                //I put this print and variables x,y,z here for debug but also to implemented it later on
                    System.out.println("x, y, z of p command are: " + x + ", " + y + ", " + z);

                } else if ("d".equals(input.next())) {
                    System.out.println("got d!");
                    String x = input.next();
                    System.out.println("x of d command: " + x);

                } else if ("s".equals(input.next())) { //This is the show status operation from 's' command
                    System.out.println("got s");
                    String x = input.next();
                    System.out.println("x of s command is: " + x);
                } else if ("q".equals(input.next())) {
                    System.out.println("got q");
                } else {
                    System.out.println("command not found");
                }
            }
        } catch (NoSuchElementException e) {
            System.out.print(e);
        }
    }
}

I am thankful for any solutions that will come from you all

Answer 1

You are skipping pieces of the file by calling input.next(). Store the result of input.next() in a variable and then use that variable in your if elses. Once you know which command you are dealing with you can call input.next() for however many inputs you are expecting for the given command.

This solution still has a problem if the file is not formatted correctly. If the command does not have the expected number of characters after it you will parse the file incorrectly. You should store the lines in a variable at the beginning of your conditionals using .nextLine() and parse the line variable from there to get your commands and avoid this issue.

Here I fixed the code for the first command:

import java.io.File;
import java.util.NoSuchElementException;
import java.util.Scanner;

public class test3 {
    public static void main(String[] args) throws Exception {
        File file = new File("file.dat");
        try {
            Scanner input = new Scanner(file);
            while (input.hasNextLine()) {
                string currentLine = input.nextLine();
                string[] currentLineArray = currentLine.split(" ");
                if ("p".equals(currentLineArray[0])) {
                    System.out.println("got p!");
                    if(currentLineArray.length == 4){
                        String x = currentLineArray[1];
                        String y = currentLineArray[2];
                        String z = currentLineArray[3];
                        System.out.println("x, y, z of p command are: " + x + ", " + y + ", " + z);
                    } else {
                        System.out.println("Incorrect number of arugments for command p!")
                    }
                }
            }
        }
    }
}

Answer 2

The problem here is that you test on input.next() which iterates over your file input, I suggest you put the result of input.next() in a variable and test on its content.

searching for a character or string in a file (java)

2 个答案: