java编写语法分析器LL1

LL(1)语法分析器可以通过构造LL(1)预测分析表来实现。下面是java代码实现LL(1)语法分析器：

1. 定义语法规则：

interface Grammar {
    Token nextToken();
    boolean S();
    boolean A();
    boolean B();
}

2. 定义语法分析器：

class Parser {
    private Grammar grammar;
    private Token lookahead;

    public Parser(Grammar grammar) {
        this.grammar = grammar;
        lookahead = grammar.nextToken();
    }

    private void consume(Token.Type type) {
        if (lookahead.getType() == type) {
            lookahead = grammar.nextToken();
        } else {
            throw new RuntimeException("Syntax error!");
        }
    }

    public boolean parse() {
        return grammar.S();
    }

    private boolean match(Token.Type type) {
        return lookahead.getType() == type;
    }
}

3. 实现语法规则：

class MyGrammar implements Grammar {
    private List<Token> tokens;
    private int index;

    public MyGrammar(List<Token> tokens) {
        this.tokens = tokens;
        index = 0;
    }

    @Override
    public Token nextToken() {
        if (index < tokens.size()) {
            return tokens.get(index++);
        } else {
            return new Token(Token.Type.EOF, "");
        }
    }

    @Override
    public boolean S() {
        if (match(Token.Type.A)) {
            A();
            return match(Token.Type.B);
        } else {
            return false;
        }
    }

    @Override
    public boolean A() {
        if (match(Token.Type.A)) {
            consume(Token.Type.A);
            return true;
        } else {
            return false;
        }
    }

    @Override
    public boolean B() {
        if (match(Token.Type.B)) {
            consume(Token.Type.B);
            return true;
        } else {
            return false;
        }
    }
}

4. 测试代码：

public class Main {
    public static void main(String[] args) {
        List<Token> tokens = new ArrayList<>();
        tokens.add(new Token(Token.Type.A, "a"));
        tokens.add(new Token(Token.Type.B, "b"));
        tokens.add(new Token(Token.Type.EOF, ""));
        Grammar grammar = new MyGrammar(tokens);
        Parser parser = new Parser(grammar);
        System.out.println(parser.parse());
    }
}

以上代码演示了如何用Java编写一个简单的LL(1)语法分析器。