java 手写词法分析器

以下是一个用Java编写的手写词法分析器的示例代码：

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class Lexer {
    private static final char EOF = (char) -1;
    private static final char EOL = '\n';
    private static final String OPERATORS = "+-*/()";
    private static final String DIGITS = "0123456789";

    private BufferedReader reader;
    private char currentChar;

    public Lexer(String fileName) throws IOException {
        reader = new BufferedReader(new FileReader(fileName));
        currentChar = (char) reader.read();
    }

    public List<Token> tokenize() throws IOException {
        List<Token> tokens = new ArrayList<>();
        while (currentChar != EOF) {
            if (currentChar == EOL) {
                consume();
                continue;
            }
            if (Character.isWhitespace(currentChar)) {
                consume();
                continue;
            }
            if (OPERATORS.indexOf(currentChar) != -1) {
                tokens.add(new Token(Token.Type.OPERATOR, Character.toString(currentChar)));
                consume();
                continue;
            }
            if (DIGITS.indexOf(currentChar) != -1) {
                StringBuilder sb = new StringBuilder();
                while (DIGITS.indexOf(currentChar) != -1) {
                    sb.append(currentChar);
                    consume();
                }
                tokens.add(new Token(Token.Type.NUMBER, sb.toString()));
                continue;
            }
            throw new RuntimeException("Invalid character: " + currentChar);
        }
        return tokens;
    }

    private void consume() throws IOException {
        currentChar = (char) reader.read();
    }
}

class Token {
    enum Type {
        OPERATOR, NUMBER
    }

    private Type type;
    private String value;

    public Token(Type type, String value) {
        this.type = type;
        this.value = value;
    }

    public Type getType() {
        return type;
    }

    public String getValue() {
        return value;
    }
}

这个词法分析器可以读取一个文件并将其分解为令牌。它支持四种类型的令牌：运算符、数字、换行符和文件结束符。它使用一个缓冲区来存储当前正在解析的符号，并使用一个符号类型的数组来存储确定模型的符号。