如何将EBNF重复实现为Java代码？

public class EBNFParser {
    private String input;
    private int index;

    public EBNFParser(String input) {
        this.input = input;
        this.index = 0;
    }

    public boolean parse() {
        return expression();
    }

    private boolean expression() {
        if (term()) {
            while (match(',')) {
                if (!term()) {
                    return false;
                }
            }
            return true;
        }
        return false;
    }

    private boolean term() {
        return match('a');
    }

    private boolean match(char c) {
        if (index < input.length() && input.charAt(index) == c) {
            index++;
            return true;
        }
        return false;
    }
}