Objectives of the project 1. To develop your understanding of lexical analyzer i

Question

Objectives of the project 1. To develop your understanding of lexical analyzer in compilers of program languages. 2. To improve you knowledge of Java programming. Topic of assignment: Lexical analyzer Write Java programs for a lexical analyzer which can identify the following tokens: 1 INT_LIT: consists of digits 2 ID_CODE: starts with a letter followed by letters and digits, and has a limited length of 10 3 ASSIGN_CODE: = 4 PLUS_CODE: + 5 MINUS_CODE: - 6 DIVISON_CODE: / 7 MULTIP_CODE: * Programs You will design two classes: TestLexAnalyzer: contains main method which performs input/output operations. LexAnalyzer: contains all the methods related to lexical analysis. Refer to the C programs in the text book for algorithm design. Input: a string of assignment statement Output: tokens of each lexeme. A running example: Input string: sum = sum + num; Output: Lexeme Token sum ID_CODE = ASSIGN_CODE sum ID_CODE + PLUS_CODE num ID_CODE using java source code

Explanation / Answer

LexAnalyzer class

public class LexAnalyzer {
String str;
public LexAnalyzer(String str1) {
   str=new String();
   str=str1;
}
void tokenize()
{ boolean check=true;
   for(int i=0;i<str.length();i++)
   {
   if(str.charAt(i)=='+'&&check)
   {
       System.out.print(" + PLUS_CODE ");
   }
   if(str.charAt(i)=='-'&&check)
   {
       System.out.print(" - PLUS_CODE ");
   }
   if(str.charAt(i)=='*'&&check)
   {
       System.out.print(" * PLUS_CODE ");
   }
   if(str.charAt(i)=='/'&&check)
   {
       System.out.print(" / PLUS_CODE ");
   }
   if(str.charAt(i)=='='&&check)
   {
       System.out.print(" = ASSIGN_CODE ");
   }
   if(str.charAt(i)=='0'||str.charAt(i)=='1'||str.charAt(i)=='2'||str.charAt(i)=='3'||str.charAt(i)=='4'||str.charAt(i)=='5'||str.charAt(i)=='6'||str.charAt(i)=='7'||str.charAt(i)=='8'||str.charAt(i)=='9')
   {
       if(check==true)
       {
           check=false;
       }
       else
       {
           if(str.charAt(i)=='0'||str.charAt(i)=='1'||str.charAt(i)=='2'||str.charAt(i)=='3'||str.charAt(i)=='4'||str.charAt(i)=='5'||str.charAt(i)=='6'||str.charAt(i)=='7'||str.charAt(i)=='8'||str.charAt(i)=='9')
           {
               System.out.print(str.charAt(i-1)+""+str.charAt(i)+" INT_LIT");
               check=true;
           }
           else
           {
               System.out.println("String contain invalid token: digit followed by character");
               break;
           }
       }
   }
   if(Character.isAlphabetic(str.charAt(i)))
   {
       int j=i;
       boolean flag=true;
       while(i<str.length()&&(Character.isAlphabetic(str.charAt(i))||Character.isDigit(str.charAt(i))))
       {
           i++;
           if(i-j>10)
           {
               System.out.println("String contain invalid token: It contain to");
               flag=false;
               break;
           }
       }
       if(!flag)
       {
           break;
       }
       else
       {
       System.out.print(str.substring(j,i)+" ID_CODE");
       i--;
       }
   }
   }
}
}

TestLexAnalyzer class

import java.util.Scanner;

public class TestLexAnalyzer {

   public static void main(String[] args) {
       Scanner sc=new Scanner(System.in);
       System.out.println("Enter the string to tokenize");
       String str=sc.nextLine();
       LexAnalyzer lexAnalyzer=new LexAnalyzer(str);
       lexAnalyzer.tokenize();
       sc.close();
       }

}

Output:

Enter the string to tokenize
sum=sum+num
sum ID_CODE = ASSIGN_CODE sum ID_CODE + PLUS_CODE num ID_CODE

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