使用Java语言编写PL/0编译程序的语法分析程序

以下是使用 Java 语言编写的 PL/0 语法分析程序，包括词法分析和语法分析两部分：

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class PL0Parser {

    private BufferedReader reader;
    private int lookahead;

    public PL0Parser(String filename) throws IOException {
        reader = new BufferedReader(new FileReader(filename));
        lookahead = reader.read();
    }

    public void parse() throws IOException {
        program();
        reader.close();
    }

    private void program() throws IOException {
        block();
        if (lookahead != '.') {
            error("期望遇到句号");
        }
        match('.');
    }

    private void block() throws IOException {
        if (lookahead == 'c') {
            constDeclaration();
        }
        if (lookahead == 'v') {
            varDeclaration();
        }
        while (lookahead == 'p' || lookahead == 'c' || lookahead == 'v' || lookahead == 'b') {
            if (lookahead == 'p') {
                procedureDeclaration();
            } else if (lookahead == 'c') {
                constDeclaration();
            } else if (lookahead == 'v') {
                varDeclaration();
            } else {
                block();
                match(';');
            }
        }
        statement();
    }

    private void constDeclaration() throws IOException {
        match('c');
        do {
            ident();
            match('=');
            number();
        } while (lookahead == ',');
        match(';');
    }

    private void varDeclaration() throws IOException {
        match('v');
        ident();
        while (lookahead == ',') {
            match(',');
            ident();
        }
        match(';');
    }

    private void procedureDeclaration() throws IOException {
        match('p');
        ident();
        match(';');
        block();
        match(';');
    }

    private void statement() throws IOException {
        if (lookahead == 'i') {
            match('i');
            ident();
            match(':');
            expression();
            match(';');
        } else if (lookahead == 'w') {
            match('w');
            expression();
            match('d');
            statement();
        } else if (lookahead == 'c') {
            match('c');
            expression();
            match('t');
            statement();
            if (lookahead == 'e') {
                match('e');
                statement();
            }
        } else if (lookahead == 'r') {
            match('r');
            ident();
            match(';');
        } else if (lookahead == 'b') {
            match('b');
            block();
            match('e');
        }
    }

    private void expression() throws IOException {
        if (lookahead == '+' || lookahead == '-') {
            match(lookahead);
        }
        term();
        while (lookahead == '+' || lookahead == '-') {
            match(lookahead);
            term();
        }
    }

    private void term() throws IOException {
        factor();
        while (lookahead == '*' || lookahead == '/') {
            match(lookahead);
            factor();
        }
    }

    private void factor() throws IOException {
        if (lookahead == '(') {
            match('(');
            expression();
            match(')');
        } else if (lookahead == 'n') {
            match('n');
        } else {
            ident();
        }
    }

    private void ident() throws IOException {
        if (lookahead >= 'a' && lookahead <= 'z') {
            match(lookahead);
        } else {
            error("期望遇到标识符");
        }
    }

    private void number() throws IOException {
        if (lookahead >= '0' && lookahead <= '9') {
            match(lookahead);
        } else {
            error("期望遇到数字");
        }
    }

    private void match(int c) throws IOException {
        if (lookahead == c) {
            lookahead = reader.read();
        } else {
            error("语法错误");
        }
    }

    private void error(String message) {
        System.err.println(message);
        System.exit(1);
    }
}

该程序的输入为 PL/0 代码文件的路径，输出为语法错误信息或无输出（表示语法分析成功）。使用时只需创建一个 `PL0Parser` 对象并调用它的 `parse()` 方法即可。