Scanner.java

package lox;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import static lox.TokenType.*;

class Scanner {
	private final String source;
	private final List<Token> tokens = new ArrayList<>();
	private int start = 0;
	private int current = 0;
	private int line = 1;

	Scanner(String source){
		this.source = source;
	}

	List<Token> scanTokens() {
		while (!isAtEnd()){
			start = current;
			scanToken();
		}

		tokens.add(new Token(EOF, "", null, line));
		return tokens;
	}

	private void scanToken(){
		char c = advance();
		switch (c) 
			case '(': addToken(LEFT_PAREN); break;
			case ')': addToken(RIGHT_PAREN); break;
			case '{': addToken(LEFT_BRACE); break;
			case '}': addToken(RIGHT_BRACE); break;
			case ',': addToken(COMMA); break;
			case '.': addToken(DOT); break;
			case '-': addToken(MINUS); break;
			case '+': addToken(PLUS); break;
			case ';': addToken(SEMICOLON); break;
			case '*': addToken(STAR); break;
			case '!':
				addToken(match('=') ? BANG_EQUAL : EQUAL);
				break;
			case '=':
				addToken(match('=') ? EQUAL_EQUAL : EQUAL);
				break;
			case '>':
				addToken(match('=') ? GREATER_EQUAL : GREATER);
				break;
			case '<':
				addToken(match('=') ? LESS_EQUAL : LESS);
				break;
			case '/':
				if(match('/'){
					while(peek() != "/n" && !isAtEnd()) advance();
				} else {
					addToken(SLASH);
				}
				break;
			case ' ':
			case '\r':
			case '\t': break;
			case 'n':
				line++;
				break;

			default: 
			Lox.error(line, "Unexpected character.");
			break;
		}
	}

	private boolean match(char expected){
		if(isAtEnd()) return false;
		if(source.charAt(current)!=expected) return false;

		current++;
		return true;
	}

	private char peek(){
		if(isAtEnd()) return '\0';
		return source.charAt(current);
	}

	private boolean isAtEnd(){
		return current >= source.length();
	}

	private char advance() {
		return source.charAt(current++);
	}

	private void addToken(TokenType type){
		addToken(type, null);
	}

	private void addToken(TokenType type, Object literal){
		String text = source.substring(start, current);
		tokens.add(new Token(type, text, literal, line))'
	} 
}