CFG java programming S->aSb | bSa | epsilon | equal number of a's and b's

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PROGRAM:- 1

Note:- this program is based on the following  cfg production rules.
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Q 1. write a java program for the cfg having equal number of a's and b's
    production rule                                                                 //file 1 readable (to be read)
      S -> aSb

      S -> bSa
      S -> ~ ( epsilon)    // the symbol  "~" denote the  epsilon

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file two= (where code of the cfg written)

code

import java.io.*;

import java.util.Scanner;

class Cfg

{

    public static void main(String args []) throws IOException

    {

        Scanner r=new Scanner(System.in);

        File file=new File("/home/rajeevkumarmahato/CG/C.java");     //first file location  

        BufferedReader br=new BufferedReader(new FileReader(file));

        String t="";

        while((t=br.readLine())!=null)

            System.out.println(t);

        System.out.println("enter the string");

        String input=r.next();

        if(input.length()%2==0)

        {

            int lastpointer=input.length()-1;

            for(int i=0;i<input.length()/2;i++)

            {

                if(input.charAt(i)=='a' && input.charAt(lastpointer)=='b')

                {

                    System.out.println("aSb");

                    lastpointer--;

                }

                else if(input.charAt(i)=='b' && input.charAt(lastpointer)=='a')

                {

                    System.out.println("bSa");

                    lastpointer--;

                }

                else

                {

                    System.out.println("not in the cfg"); 
                     break;

                }

            }

        }

        else

        {

            System.out.println("Not belongs to the cfg");

        }

    }

}

Example;-

1.

2.

compiler Design