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0133_解释器模式(Interpreter)

news 2025/9/20 21:27:51

解释器模式(Interpreter)

意图

给定一种语言，定义它的文法的一种表示，并定义一个解释器，这个解释器使用该表示来解释语言中的句子。

UML 图

优点

易于扩展文法：由于使用类来表示语言的文法规则，可以通过继承来扩展文法
易于实现文法：实现文法中的每个规则都很简单，可以方便地改变和扩展文法
增加新的解释表达式方便：增加新的解释表达式不需要修改现有表达式
可组合性：可以通过组合多个表达式来构建复杂的解释器

缺点

复杂文法难以维护：对于复杂的文法，解释器模式会定义过多的类，导致系统变得复杂
执行效率较低：由于通常使用递归调用，解释器的执行效率可能较低
应用场景有限：适用于简单的文法，复杂文法需要使用其他技术如编译器或解析器生成器
难以扩展复杂操作：添加新的操作需要修改所有表达式类

代码示例

以机器人指令解释系统为例：

1. 抽象表达式接口 (Abstract Expression)

// 抽象表达式接口
public interface RobotExpression {int interpret(RobotContext context);String getDescription();
}

2. 终结符表达式 (Terminal Expressions)

// 移动指令
public class MoveExpression implements RobotExpression {private int distance;public MoveExpression(int distance) {this.distance = distance;}@Overridepublic int interpret(RobotContext context) {context.addToLog("移动 " + distance + " 米");return distance;}@Overridepublic String getDescription() {return "移动 " + distance + " 米";}
}// 转向指令
public class TurnExpression implements RobotExpression {private String direction;public TurnExpression(String direction) {this.direction = direction;}@Overridepublic int interpret(RobotContext context) {context.addToLog("转向 " + direction);return 0; // 转向不消耗能量}@Overridepublic String getDescription() {return "转向 " + direction;}
}// 抓取指令
public class GrabExpression implements RobotExpression {private String object;public GrabExpression(String object) {this.object = object;}@Overridepublic int interpret(RobotContext context) {context.addToLog("抓取 " + object);return 5; // 抓取消耗5单位能量}@Overridepublic String getDescription() {return "抓取 " + object;}
}

3. 非终结符表达式 (Nonterminal Expressions)

// 重复指令
public class RepeatExpression implements RobotExpression {private int times;private RobotExpression expression;public RepeatExpression(int times, RobotExpression expression) {this.times = times;this.expression = expression;}@Overridepublic int interpret(RobotContext context) {int totalEnergy = 0;context.addToLog("开始重复 " + times + " 次");for (int i = 0; i < times; i++) {context.addToLog("第 " + (i+1) + " 次执行:");totalEnergy += expression.interpret(context);}context.addToLog("重复执行完成");return totalEnergy;}@Overridepublic String getDescription() {return "重复 " + times + " 次: " + expression.getDescription();}
}// 序列指令
public class SequenceExpression implements RobotExpression {private List<RobotExpression> expressions = new ArrayList<>();public void addExpression(RobotExpression expression) {expressions.add(expression);}@Overridepublic int interpret(RobotContext context) {int totalEnergy = 0;context.addToLog("开始执行序列指令");for (RobotExpression expression : expressions) {totalEnergy += expression.interpret(context);}context.addToLog("序列指令执行完成");return totalEnergy;}@Overridepublic String getDescription() {StringBuilder sb = new StringBuilder("序列指令: [");for (int i = 0; i < expressions.size(); i++) {if (i > 0) sb.append(", ");sb.append(expressions.get(i).getDescription());}sb.append("]");return sb.toString();}
}

4. 上下文类 (Context)

// 上下文类
public class RobotContext {private int x = 0;private int y = 0;private String direction = "北";private List<String> log = new ArrayList<>();private int energyConsumed = 0;public void addToLog(String message) {log.add(message);}public List<String> getLog() {return new ArrayList<>(log);}public void clearLog() {log.clear();}public void addEnergyConsumed(int energy) {this.energyConsumed += energy;}public int getEnergyConsumed() {return energyConsumed;}public String getPosition() {return "(" + x + ", " + y + ")";}public String getDirection() {return direction;}// 更新位置和方向的方法public void updatePosition(int distance) {switch (direction) {case "北": y += distance; break;case "南": y -= distance; break;case "东": x += distance; break;case "西": x -= distance; break;}}public void updateDirection(String newDirection) {this.direction = newDirection;}
}

5. 指令解析器 (Parser)

// 指令解析器
public class RobotInstructionParser {public static RobotExpression parse(String instruction) {if (instruction.startsWith("MOVE")) {int distance = Integer.parseInt(instruction.substring(5));return new MoveExpression(distance);}else if (instruction.startsWith("TURN")) {String dir = instruction.substring(5);return new TurnExpression(dir);}else if (instruction.startsWith("GRAB")) {String obj = instruction.substring(5);return new GrabExpression(obj);}else if (instruction.startsWith("REPEAT")) {String[] parts = instruction.split(" ");int times = Integer.parseInt(parts[1]);String subInstruction = instruction.substring(instruction.indexOf(' ', 7) + 1);RobotExpression subExpression = parse(subInstruction);return new RepeatExpression(times, subExpression);}else if (instruction.startsWith("SEQUENCE")) {SequenceExpression sequence = new SequenceExpression();String[] subInstructions = instruction.substring(9).split(";");for (String subInstruction : subInstructions) {sequence.addExpression(parse(subInstruction.trim()));}return sequence;}throw new IllegalArgumentException("无法解析指令: " + instruction);}
}

6. 客户端代码

public class InterpreterPatternDemo {public static void main(String[] args) {System.out.println("=== 解释器模式演示 - 机器人指令系统 ===\n");// 创建上下文RobotContext context = new RobotContext();// 解析并执行简单指令System.out.println("1. 执行简单指令:");RobotExpression move = RobotInstructionParser.parse("MOVE 10");RobotExpression turn = RobotInstructionParser.parse("TURN 东");RobotExpression grab = RobotInstructionParser.parse("GRAB 箱子");System.out.println("指令: " + move.getDescription());int energy1 = move.interpret(context);System.out.println("消耗能量: " + energy1 + "\n");System.out.println("指令: " + turn.getDescription());int energy2 = turn.interpret(context);System.out.println("消耗能量: " + energy2 + "\n");System.out.println("指令: " + grab.getDescription());int energy3 = grab.interpret(context);System.out.println("消耗能量: " + energy3 + "\n");// 解析并执行复杂指令System.out.println("2. 执行复杂指令:");RobotExpression repeat = RobotInstructionParser.parse("REPEAT 3 MOVE 5");System.out.println("指令: " + repeat.getDescription());context.clearLog();int energy4 = repeat.interpret(context);// 显示执行日志System.out.println("\n执行日志:");for (String logEntry : context.getLog()) {System.out.println("  " + logEntry);}System.out.println("总消耗能量: " + energy4 + "\n");// 解析并执行序列指令System.out.println("3. 执行序列指令:");RobotExpression sequence = RobotInstructionParser.parse("SEQUENCE MOVE 8; TURN 南; MOVE 5; GRAB 物品");System.out.println("指令: " + sequence.getDescription());context.clearLog();int energy5 = sequence.interpret(context);System.out.println("\n执行日志:");for (String logEntry : context.getLog()) {System.out.println("  " + logEntry);}System.out.println("总消耗能量: " + energy5);System.out.println("最终位置: " + context.getPosition());System.out.println("最终方向: " + context.getDirection());System.out.println("\n=== 演示完成 ===");}
}