Searching for a String in a .txt file and getting the row and column number in Java

Question

I am currently stuck with a problem. I am supposed to write a programm that is able to search for a string in a .txt file given as argument. The programm must return the row and the column of the found string. I am struggling to find a way to achieve that and have no idea how to go on. I would be very happy to hear from you.

Here is my attempt in tackling with my task: - I thought about saving the content of a file via a buffered reader in a string array, but that does not seem to work since I cannot define the length of the array from the beginning - I also thought about saving the content of the file via a buffered reader in a string and then split this string in characters. However I am not sure how I will be able to retreieve the rows in the original file then.

This is the non-functional code that I have at the moment:

public class StringSearch{
    public static void main(String[] args){
        if(args.length > 0){
            BufferedReader br = null;
            String text = null;
            try{
                br = new BufferedReader(new FileReader(args[0]));
                // attempt of saving the content of the "argument" file in a string array and then in a        string
                String[] lines = new String[]; // I know this does not work like this 
                for( int i = 0; i < lines.length; i++){
                    lines[i] = br.readLine;
                    text = text + lines[i];
                    i++;
                }
                text.split("\r\n");

            } catch (IOException ioe){
                ioe.printStackTrace();
            } finally{
                if (br != null) {
                    try{
                        br.close();
                    }catch (IOException ioe){
                        ioe.printStackTrace();
                    }
                }


            }

        }
    }
}

Answer 1

Here's one approach -

1. Let's consider a counter which holds a counter for all the readLine() method invocations - representing the "row" in the .txt file. So, increment the counter after every readLine call in the while loop.
2. Next, split the line on " " (space) to get an array of each word in the line. Then, you could iterate over this array and match the word to the search string. The position of array index at the time the match was found will represent the "column".

Answer 2

You can do it as follows:

import java.io.File;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        if (args.length != 2) {
            System.out.println("The correct syntax to use this program is: java Main <filename.txt> <text-to-search>");
            return;
        }
        Scanner scanner;
        File file = new File(args[0]);
        int rowCount = 1, index;
        String line;

        // Map to collect row and col info of the search string
        Map<String, String> lineColMap = new HashMap<String, String>();

        if (!file.exists()) {
            System.out.println("The file, " + args[0] + " does not exist");
            return;
        }
        try {
            scanner = new Scanner(file);
            while (scanner.hasNextLine()) {// Loop until the last line in the file
                line = scanner.nextLine();// Read a line from the file
                index = line.indexOf(args[1]);// Find if the string exists in the line
                if (index != -1) {// If the string exists
                    // Put the row and col info of the search string into the map
                    lineColMap.put("Row: " + rowCount, "Column: " + index);
                }
                rowCount++;// Increase the row count
            }
        } catch (Exception e) {
            System.out.println("Error occured while processing the file");
            e.printStackTrace();
        }
        if (lineColMap.entrySet().size() > 0) {// If there is at least one entry collected into the map
            System.out.println("'" + args[1] + "' exists in " + args[0] + " as follows:");
            for (Map.Entry<String, String> entry : lineColMap.entrySet()) {
                System.out.println(entry.getKey() + ", " + entry.getValue());
            }
        } else {
            System.out.println("'" + args[1] + "' does not exist in " + args[0]);
        }
    }
}

A sample run: java Main input.txt of

'of' exists in input.txt as follows:
Row: 1, Column: 51
Row: 2, Column: 50
Row: 3, Column: 50
Row: 5, Column: 71

The content of input.txt is as follows:

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The logic in the code is straight forward and I believe, you should be able to understand it in the first reading. Feel free to comment in case of any doubt.