本次实验属于模仿型实验，通过本次实验学生将掌握以下内容： 

1、理解解释器模式的动机，掌握该模式的结构；

2、能够利用解释器模式解决实际问题。

[实验任务一]：解释器模式

某机器人控制程序包含一些简单的英文指令，其文法规则如下：

expression ::= direction action distance | composite

composite ::= expression and expression

direction ::= ‘up’ | ‘down’ | ‘left’ | ‘right’

action ::= ‘move’ | ‘run’

distance ::= an integer //一个整数值

如输入：up move 5，则输出“向上移动5个单位”；输入：down run 10 and left move 20，则输出“向下移动10个单位再向左移动20个单位”。

实验要求：

1. 提交类图；

2. 提交源代码；

3. 注意编程规范。

1、类图

源代码

package org.example;

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

class Command {
    String direction;
    String action;
    int distance;

    public Command(String direction, String action, int distance) {
        this.direction = direction;
        this.action = action;
        this.distance = distance;
    }

    @Override
    public String toString() {
        return "向" + direction + " " + action + " " + distance + "个单位";
    }
}

package org.example;

import java.util.ArrayList;
import java.util.List;

class Parser {
    private String input;
    private int index = 0;

    public Parser(String input) {
        this.input = input.trim(); // 去除输入字符串的首尾空格
    }

    // 解析主入口
    public List<Command> parse() {
        List<Command> commands = new ArrayList<>();
        while (index < input.length()) {
            Command command = parseExpression();
            commands.add(command);
            skipWhitespace();


            // 如果下一个部分是 'and'，则继续解析复合指令
            if (index < input.length() && input.startsWith("and", index)) {
                index += 3; // 跳过 "and"
                // 跳过可能的空格
                skipWhitespace();
            }
        }
        return commands;
    }


    // 解析一个表达式（可能是简单指令或复合指令）
    private Command parseExpression() {
        if (input.startsWith("up", index) || input.startsWith("down", index) || input.startsWith("left", index) || input.startsWith("right", index)) {
            return parseSimpleExpression();
        } else {
            throw new IllegalArgumentException("Invalid expression at index " + index + " in input: '" + input.substring(index) + "'");
        }
    }

    // 解析简单指令（方向 + 动作 + 距离）
    private Command parseSimpleExpression() {
        String direction = parseDirection();
        String action = parseAction();
        int distance = parseDistance();
        return new Command(direction, action, distance);
    }

    // 解析方向（up, down, left, right）
    private String parseDirection() {
        if (input.startsWith("up", index)) {
            index += 2;
            return "上";
        } else if (input.startsWith("down", index)) {
            index += 4;
            return "下";
        } else if (input.startsWith("left", index)) {
            index += 4;
            return "左";
        } else if (input.startsWith("right", index)) {
            index += 5;
            return "右";
        } else {
            throw new IllegalArgumentException("Invalid direction at index " + index);
        }
    }

    // 解析动作（move, run）
    private String parseAction() {
        skipWhitespace(); // 跳过空格
        // 跳过可能的空格
        while (index < input.length() && input.charAt(index) == ' ') {
            index++;
        }
        if (input.startsWith("move", index)) {
            index += 4;
            return "移动";
        } else if (input.startsWith("run", index)) {
            index += 3;
            return "奔跑";
        } else {
            throw new IllegalArgumentException("Invalid action at index " + index);
        }
    }

    // 解析距离（整数）
    private int parseDistance() {
        skipWhitespace(); // 跳过空格
        while (index < input.length() && input.charAt(index) == ' ') { // 跳过空格
            index++;
        }
        int start = index;
        while (index < input.length() && Character.isDigit(input.charAt(index))) {
            index++;
        }
        if (start == index) {
            throw new IllegalArgumentException("Invalid distance at index " + start);
        }
        return Integer.parseInt(input.substring(start, index));
    }
    // 跳过空格
    private void skipWhitespace() {
        while (index < input.length() && input.charAt(index) == ' ') {
            index++;
        }
    }
}

package org.example;

import java.util.List;
import java.util.Scanner;

public class RobotControl {
    public static void main(String[] args) {
        // 创建 Scanner 用于读取用户输入
        Scanner scanner = new Scanner(System.in);

        // 循环接受用户输入
        while (true) {
            System.out.print("请输入指令 (或输入 'exit' 退出): ");
            String input = scanner.nextLine().trim();

            // 如果输入 'exit' 则退出程序
            if (input.equalsIgnoreCase("exit")) {
                System.out.println("程序结束！");
                break;
            }

            // 创建 Parser 对象并解析指令
            Parser parser = new Parser(input);
            List<Command> commands = parser.parse();

            // 输出解析结果
            for (int i = 0; i < commands.size(); i++) {
                // 如果是最后一个命令，不加 "再"
                if (i == commands.size() - 1) {
                    System.out.println(commands.get(i));
                } else {
                    System.out.print(commands.get(i) + "再");
                }
            }
        }

        scanner.close();  // 关闭扫描器
    }
}

3、运行截图