用java写一个词法分析器

好的，我可以为你提供一个基于 Java 的简单词法分析器实现。你可以参考以下代码：

public class Lexer {
    private String input;
    private int currentPosition;

    public Lexer(String input) {
        this.input = input;
        this.currentPosition = 0;
    }

    public Token getNextToken() {
        while (currentPosition < input.length()) {
            char currentChar = input.charAt(currentPosition);

            if (Character.isDigit(currentChar)) {
                return new Token(TokenType.INTEGER, readInteger());
            }

            if (Character.isLetter(currentChar)) {
                return new Token(TokenType.IDENTIFIER, readIdentifier());
            }

            if (currentChar == '+') {
                currentPosition++;
                return new Token(TokenType.PLUS, "+");
            }

            if (currentChar == '-') {
                currentPosition++;
                return new Token(TokenType.MINUS, "-");
            }

            if (currentChar == '*') {
                currentPosition++;
                return new Token(TokenType.MULTIPLY, "*");
            }

            if (currentChar == '/') {
                currentPosition++;
                return new Token(TokenType.DIVIDE, "/");
            }

            if (currentChar == '(') {
                currentPosition++;
                return new Token(TokenType.LEFT_PAREN, "(");
            }

            if (currentChar == ')') {
                currentPosition++;
                return new Token(TokenType.RIGHT_PAREN, ")");
            }

            if (currentChar == '=') {
                currentPosition++;
                return new Token(TokenType.EQUALS, "=");
            }

            if (currentChar == ';') {
                currentPosition++;
                return new Token(TokenType.SEMICOLON, ";");
            }

            if (Character.isWhitespace(currentChar)) {
                skipWhitespace();
                continue;
            }

            throw new RuntimeException("Invalid token: " + currentChar);
        }

        return new Token(TokenType.EOF, "");
    }

    private String readInteger() {
        StringBuilder sb = new StringBuilder();

        while (currentPosition < input.length() && Character.isDigit(input.charAt(currentPosition))) {
            sb.append(input.charAt(currentPosition));
            currentPosition++;
        }

        return sb.toString();
    }

    private String readIdentifier() {
        StringBuilder sb = new StringBuilder();

        while (currentPosition < input.length() && Character.isLetterOrDigit(input.charAt(currentPosition))) {
            sb.append(input.charAt(currentPosition));
            currentPosition++;
        }

        return sb.toString();
    }

    private void skipWhitespace() {
        while (currentPosition < input.length() && Character.isWhitespace(input.charAt(currentPosition))) {
            currentPosition++;
        }
    }
}

这是一个简单的词法分析器，它可以识别整数、标识符、运算符等。你可以根据需要修改或扩展它以适应你的具体需求。