Consider the grammar of expressions provided in file `grammar. txt` in project 1. Write a parser for the given grammar. The parser will use the scanner (written in project 1) to process a file and return true or false, depending on whether the input is syntactically correct according to the given grammar.

// java program to validate a given sentence

// for set of rules

class GFG

{

// Method to check a given sentence for given rules static boolean checkSentence(char[] str)

{

//Calculate the length of the string.

int len=str.length;

//Check that the first character lies in [A-Z].

//Otherwise return false.

if(str[0] < 'A' || str[0] > 'Z')

return false;

// Maintain 2 states. Previous and current state

// based on which vertex state you are.

// initialise both with 0 = start state.

int prev_state = 0,curr_state = 0;

// Keep the index to the next character in the string.

int index = 1;

// Loop to go over the string.

while(index <= str.length)

{

// Set states according to the input characters

// If current character is [A-Z]. Set current state as 0.

if(str[index]>='A'&&str[index]<='Z')

curr_state=0;

// If current character is a space.

// Set current state as 1.

else if(str[index]=='')

curr_state=1;

// If current character is[a-z].

// Set current state as 2.

else if (str[index]>='&&str[index]<='z')

curr_state=2;

// If current state is a dot(.).

// set current state as 3.

else if(str[index]=='.')

curr_state=3;

// Validates all current state with previous state

// for the rules in the description of the problem.

if (prev_state==curr_state&&curr_state !=2)

return false;

if(prev_state==2&&curr_state==0)

return false;

// If we have reached last state and previous state

// is not 1, then check next character. if next character

// is '\0', then return true, else false

if (curr_state==3&&prev_state!=1)

return(index + 1==str.length);

index++;

// Set previous state as current state

// beforw going over to the next character.

prev_state=curr_state;

}

return false;

}

//Driver Code

public static void main(String[] args)

{

String[] str={"i love cinema.", "The vertex is S.",

"I am single.", "My name is KG.",

 "I love cinema.", "GeeksQuiz. is a quiz site.",

"I love Geeksquiz and Geeksforgeeks.",

"You are my friend.", "I love cinema"};

int str_size=str.length;

int i=0;

for(i=0; i<str_size;i++)

{

if(checkSentence(str[i].toCharArray()))

 System.Out.Println("\""+str[i]+"\""+"is correct");

else

System.Out.Println("\""+str[i]+"\""+"is incorrect");

}

}

}

Explanation:

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