In this project, you will implement a simple lexical analyzer to scan a small se

Question

In this project, you will implement a simple lexical analyzer to scan a small set of expressions. This set of expressions has the following tokens: identifier, integer constant, left parenthesis, right parenthesis, addition operator, and multiplication operator. Specifically, assume we have the following lexical definition. LETTER rightarrow a | b | ... | z | A | ... | Z DIGIT rightarrow 0 | 1 | ... | 9 We define a set of tokens as follows. ID rightarrow LETTER {LETTER | DIGIT} INT rightarrow DIGIT {DIGIT} LEFT_PARENTHESIS rightarrow (RIGHT_PARENTHESIS rightarrow) ADD_OP rightarrow ' + ' | '-' MUL_OP rightarrow ' + ' | '/' Note that blank is a character that should be skipped by the program. Given an expression as input, your program should accomplish the following requirements: If the expression has error, for example, undefined token, unequal numbers of left parenthesis and right parenthesis, the program should output an error message. Print out all identifiers and all integer constants; Counting how many left parenthesis, right parenthesis, addition, and multiplication operators. For example, for the input expression (number1 + number2) * (number3 + 1000) your program should output ID: number1, number2, number3 INT: 1000 The numbers of LEFT PARENTHESIS, RIGHT PARENTHESIS, ADD_OP and MUL_OP: 2, 2, 2, and 1

Explanation / Answer

import java.util.*;

//Class Expression definition
public class Expression
{
   //Main method
   public static void main(String ss[])
   {
       //Scanner class object created to accept data
       Scanner sc = new Scanner(System.in);
       System.out.println("Enter a expression");
       //Accept an expression      
       String exp = sc.nextLine();
       //To store identifiers
       String strID = "ID:";
       //To store integers
       String strINT = "INT:";
       //To store frequency of left parenthesis, right parenthesis, addition and multiplication symbol
       int lp, rp, add, mul;
       //Initially all are zero
       lp = rp = add = mul = 0;
       //Loop till end of the expression
       for(int c = 0; c < exp.length(); c++)
       {
           //Extracts the character
           char ch = exp.charAt(c);
           //If the character is a digit
           if(Character.isDigit(ch))
           {
               //Extract all the characters till right parenthesis or space
               do
               {
                   //Concatenate the current character with strINT
                   strINT += exp.charAt(c);
                   //Increase the counter
                   c++;
                   //Checks for the space if true break
                   if(exp.charAt(c) == ' ')
                       break;
                   //Checks for the right parenthesis if true break
                   else if(exp.charAt(c) == ')')
                       break;
               }while(true);
               //Adds a comma at the end
               strINT += ", ";
               c--;
           }//End of if
           //If the character is a alphabet
           else if(Character.isLetter(ch))
           {
               //Extract all the characters till right parenthesis or space
               do
               {
                   //Concatenate the current character with strID
                   strID += exp.charAt(c);
                   //Increase the counter
                   c++;
                   //Checks for the space if true break
                   if(exp.charAt(c) == ' ')
                       break;
                   //Checks for the right parenthesis if true break
                   else if(exp.charAt(c) == ')')
                       break;
               }while(true);
               //Adds a comma at the end
               strID += ", ";
               c--;
           }//end of else if
           //If the character is a left parenthesis
           else if(ch == '(')
               //Increase left parenthesis counter
               lp++;
           //If the character is a right parenthesis
           else if(ch == ')')
               //Increase right parenthesis counter
               rp++;
           //If the character is a addition operator
           else if(ch == '+')
               //Increase addition operator counter
               add++;
           //If the character is a multiplication operator
           else if(ch == '*')
               //Increase multiplication operator counter
               mul++;
       }//End of for loop
       //Displays information
       System.out.println(strID);
       System.out.println(strINT);
       System.out.println("The numbers of LEFT PARENTHESIS, RIGHT PARENTHESIS, ADD_OP and MUL_OP");
       System.out.println(lp + ", " + rp + ", " + add + ", " + mul);
   }//End of main method
}//End of class

Sample Run 1:

Enter a expression
(number1 + number2) * (22 + 10)
ID:number1, number2,
INT:22, 10,
The numbers of LEFT PARENTHESIS, RIGHT PARENTHESIS, ADD_OP and MUL_OP
2, 0, 2, 1

Sample Run 2:

Enter a expression
res = ((number1 + number2) * (val1 * 10) + 30 * val3)
ID:res, number1, number2, val1, val3,
INT:10, 30,
The numbers of LEFT PARENTHESIS, RIGHT PARENTHESIS, ADD_OP and MUL_OP
3, 3, 2, 3

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