PL/0语言词法分析器：实现词元序列输出

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

public class PL0Tokenizer {
    
    private static final Map<String, String> RESERVED_WORDS = new HashMap<>();
    private static final Map<String, String> OPERATORS = new HashMap<>();
    private static final Map<String, String> DELIMITERS = new HashMap<>();
    
    static {
        RESERVED_WORDS.put('begin', 'beginsym');
        RESERVED_WORDS.put('call', 'callsym');
        RESERVED_WORDS.put('const', 'constsym');
        RESERVED_WORDS.put('do', 'dosym');
        RESERVED_WORDS.put('end', 'endsym');
        RESERVED_WORDS.put('if', 'ifsym');
        RESERVED_WORDS.put('odd', 'oddsym');
        RESERVED_WORDS.put('procedure', 'proceduresym');
        RESERVED_WORDS.put('read', 'readsym');
        RESERVED_WORDS.put('then', 'thensym');
        RESERVED_WORDS.put('var', 'varsym');
        RESERVED_WORDS.put('while', 'whilesym');
        RESERVED_WORDS.put('write', 'writesym');
        
        OPERATORS.put('+', 'plus');
        OPERATORS.put('-', 'minus');
        OPERATORS.put('*', 'times');
        OPERATORS.put('/', 'slash');
        OPERATORS.put('odd', 'oddsym');
        OPERATORS.put('=', 'eql');
        OPERATORS.put('<>', 'neq');
        OPERATORS.put('<', 'lss');
        OPERATORS.put('<=', 'leq');
        OPERATORS.put('>', 'gtr');
        OPERATORS.put('>=', 'geq');
        OPERATORS.put(':=', 'becomes');
        
        DELIMITERS.put('(', 'lparen');
        DELIMITERS.put(')', 'rparen');
        DELIMITERS.put(',', 'comma');
        DELIMITERS.put(';', 'semicolon');
        DELIMITERS.put('.', 'period');
    }
    
    public static void main(String[] args) {
        try {
            BufferedReader reader = new BufferedReader(new FileReader('input.txt'));
            BufferedWriter writer = new BufferedWriter(new FileWriter('output.txt'));
            
            String line;
            while ((line = reader.readLine()) != null) {
                String[] tokens = line.split('\s+|(?<=[(),;.])|(?=[(),;.])');
                for (String token : tokens) {
                    if (!token.isEmpty()) {
                        String tokenType = getTokenType(token);
                        writer.write('( ' + tokenType + ', ' + token + ' )\n');
                    }
                }
            }
            
            reader.close();
            writer.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    
    private static String getTokenType(String token) {
        if (RESERVED_WORDS.containsKey(token)) {
            return RESERVED_WORDS.get(token);
        } else if (isIdentifier(token)) {
            return 'IDENT';
        } else if (isNumber(token)) {
            return 'NUMBER';
        } else if (OPERATORS.containsKey(token)) {
            return OPERATORS.get(token);
        } else if (DELIMITERS.containsKey(token)) {
            return DELIMITERS.get(token);
        } else {
            throw new IllegalArgumentException('Unknown token: ' + token);
        }
    }
    
    private static boolean isIdentifier(String token) {
        return token.matches('[A-Z][A-Z0-9]*');
    }
    
    private static boolean isNumber(String token) {
        return token.matches('\d+');
    }
}