Question

: Create a Java program that will accept a regular expression and a filename for a text file. The program will process the file, looking at every line to find matches for the regular expression and display them.

Regular Expression Format : The following operators need to be accepted:

+ - one or more of the following character (no groups)

* - zero or more of the following character (no groups)

[] – no negation, no character spans – the only format is explicit, for example [0123456789]

NOTE: You do not have to implement every possible regular expression. Only the 3 above are needed.

Input: Your program should take two command line arguments. The first should be the regular exception, the second should be the filename.

Output: The output from your program should be formatted exactly like this: Match found on line 10, starting at position 10 and ending at position 25: aaaaaaaaaaaaaa0 If the regular expression entered was a*[01] And the input file contained at line 10: Xxdsdsasdaaaaaaaaaaaaaaa0 Restrictions Your program must implement its own regular expression functionality – you cannot use the built-in regular expression mechanism, nor can you include one from a package or JAR file unless you created it and included the source code in your submission. Therefore, you cannot use any pattern matching methods in any programming language.

Code:

import java.util.*;
import java.io.*;
class Regex
{
public static void main(String args[]) throws Exception {
String pattern = args[0];
BufferedReader br = new BufferedReader(new FileReader(args[1]));
String line;
boolean flag = false, flag2 = false;
int lineNumber = 1;
while((line = br.readLine()) != null){
//here ist the error
flag = findMatches(line, pattern, lineNumber);
if(flag == true)
{
// once when the item was found , the flag2 will be true. so now we can
// Output a message if there was no items found
flag2 = true;
}

lineNumber++;
}
if(flag2 == false)
{
System.out.println("No match was found");
}
}

public static boolean findMatches(String st, String p, int lineNumber) {
int n = st.length();
String temp;
boolean flag = false;
for(int i=0;i<=n;i++){
for(int j=i+1;j<=n;j++) {
temp = st.substring(i, j);
if(isMatch(temp, p)){
flag = true;
System.out.println("Match found on line " + lineNumber + ", sttarting at postition " + (i+1) + " and ending at postition " + j + ": " + temp);
  
}
}
}
return flag;

}

public static boolean isMatch(String st, String p){

//fill this out

}
}

Answer 1

PLEASE GIVE IT A THUMBS UP, I SERIOUSLY NEED ONE, IF YOU NEED ANY MODIFICATION THEN LET ME KNOW, I WILL DO IT FOR YOU

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

class Regex {

  public static void main(String args[])throws Exception {
    String pattern = args[0];

    BufferedReader br = new BufferedReader(new FileReader(args[2]));

    String line;

    int lineNumber = 1;

    while ((line = br.readLine()) != null) {
      findMatches(line, pattern, lineNumber);

      lineNumber++;
    }
  }

  public static void findMatches(String s, String p, int lineNumber) {
    int n = s.length();

    String temp;

    for (int i = 0; i < n; i++) {
      for (int j = i + 1; j <= n; j++) {
        temp = s.substring(i, j);

        if (isMatch(temp, p)) {
          System.out.println(
            "Match found on line " +
            lineNumber +
            ", starting at position " +
            (i + 1) +
            " and ending at position " +
            j +
            ": " +
            temp
          );
        }
      }
    }
  }

  public static boolean isMatch(String s, String p) {
    boolean[][] d = new boolean[s.length() + 1][p.length() + 1];

    d[0][0] = true;

    for (int i = 0; i < p.length(); ++i) {
      char current = p.charAt(i);

      if (current == '*') {
        for (int j = 0; j < s.length(); ++j) {
          d[j + 1][i + 1] = d[j + 1][i - 1];
        }

        for (int j = 0; j < s.length(); ++j) {
          if ((p.charAt(i - 1) == '.') || (p.charAt(i - 1) == s.charAt(j))) {
            d[j + 1][i + 1] = d[j + 1][i + 1] || d[j][i - 1] || d[j][i + 1];
          }
        }
      } else if (current == '.') {
        for (int j = s.length() - 1; j >= 0; --j) {
          d[j + 1][i + 1] = d[j][i];
        }
      } else {
        for (int j = 0; j < s.length(); ++j) {
          if (s.charAt(j) == p.charAt(i)) {
            d[j + 1][i + 1] = d[j][i];
          }
        }
      }
    }

    return d[s.length()][p.length()];
  }
}