/**
* Name: Tokenizer.java
*
* Remind:
* 1. Your job is to implement next() method.
* 2. Please do not modify anything else.
* 3. Check the correctness of implementation via “TokenizerTest.java” before the submission.
* 4. You may create additional fields or methods to finish your implementation.
*
* The given code is provided to assist you to complete the required tasks. But the
* given code is often incomplete. You have to read and understand the given code
* carefully, before you can apply the code properly. You might need to implement
* additional procedures, such as error checking and handling, in order to apply the
* code properly.
*/
public class MyTokenizer extends Tokenizer {
private String _buffer; //save text
private Token currentToken; //save token extracted from next()
/**
* Tokenizer class constructor
* The constructor extracts the first token and save it to currentToken
* **** please do not modify this part ****
*/
public MyTokenizer(String text) {
_buffer = text; // save input text (string)
next(); // extracts the first token.
}
/**
* This function will find and extract a next token from {@code _buffer} and
* save the token to {@code currentToken}.
*/
public void next() {
_buffer = _buffer.trim(); // remove whitespace
if(_buffer.isEmpty()) {
currentToken = null; // if there’s no string left, set currentToken null and return
return;
}
char firstChar = _buffer.charAt(0);
if(firstChar == ‘+’)
currentToken = new Token(“+”, Token.Type.ADD);
if(firstChar == ‘-‘)
currentToken = new Token(“-“, Token.Type.SUB);
// TODO: Implement multiplication and division tokenising
// TODO: Implement left round bracket and right round bracket
// TODO: Implement integer literal tokenising
// HINT: Character.isDigit() may be useful
// ########## YOUR CODE STARTS HERE ##########
if(firstChar == ‘*’) //multiply
currentToken = new Token(“*”, Token.Type.MUL);
if(firstChar == ‘/’) //divide
currentToken = new Token(“/”, Token.Type.DIV);
if(firstChar == ‘(‘) //left bracket
currentToken = new Token(“(“, Token.Type.LBRA);
if(firstChar == ‘)’) //right bracket
currentToken = new Token(“)”, Token.Type.RBRA);
if(Character.isDigit(firstChar)) //integer
{
String t = “”;
t += firstChar;
int n =1;
while (Character.isDigit(_buffer.charAt(n))){
t = t+_buffer.charAt(n);
n++;
}
currentToken = new Token(t, Token.Type.INT);
}
// ########## YOUR CODE ENDS HERE ##########
// Remove the extracted token from buffer
int tokenLen = currentToken.token().length();
_buffer = _buffer.substring(tokenLen);
}
/**
* returned the current token extracted by {@code next()}
* **** please do not modify this part ****
*
* @return type: Token
*/
public Token current() {
return currentToken;
}
/**
* check whether there still exists another tokens in the buffer or not
* **** please do not modify this part ****
*
* @return type: boolean
*/
public boolean hasNext() {
return currentToken != null;
}
}