行为型模式 - 解释器模式 (Interpreter Pattern)

解释器模式是一种行为设计模式，它定义了一个语言的文法，并且建立一个解释器来解释该语言中的句子。

需求描述:

实现一个简单的数学表达式解释器，支持加法和减法运算。例如，对于表达式 "3 + 5 - 2"，能够正确计算出结果。

java 复制代码

import java.util.Stack;

// 抽象表达式接口
interface Expression {
    int interpret();
}

// 数字表达式类
class NumberExpression implements Expression {
    private int number;

    public NumberExpression(int number) {
        this.number = number;
    }

    @Override
    public int interpret() {
        return number;
    }
}

// 加法表达式类
class AddExpression implements Expression {
    private Expression left;
    private Expression right;

    public AddExpression(Expression left, Expression right) {
        this.left = left;
        this.right = right;
    }

    @Override
    public int interpret() {
        return left.interpret() + right.interpret();
    }
}

// 减法表达式类
class SubtractExpression implements Expression {
    private Expression left;
    private Expression right;

    public SubtractExpression(Expression left, Expression right) {
        this.left = left;
        this.right = right;
    }

    @Override
    public int interpret() {
        return left.interpret() - right.interpret();
    }
}

// 解释器类
class ExpressionParser {
    public Expression parse(String expression) {
        String[] tokens = expression.split(" ");
        Stack<Expression> stack = new Stack<>();

        for (String token : tokens) {
            if (isNumber(token)) {
                stack.push(new NumberExpression(Integer.parseInt(token)));
            } else if (token.equals("+")) {
                Expression right = stack.pop();
                Expression left = stack.pop();
                stack.push(new AddExpression(left, right));
            } else if (token.equals("-")) {
                Expression right = stack.pop();
                Expression left = stack.pop();
                stack.push(new SubtractExpression(left, right));
            }
        }
        return stack.pop();
    }

    private boolean isNumber(String token) {
        try {
            Integer.parseInt(token);
            return true;
        } catch (NumberFormatException e) {
            return false;
        }
    }
}

// 客户端代码
public class MathExpressionInterpreter {
    public static void main(String[] args) {
        String expression = "3 + 5 - 2";
        ExpressionParser parser = new ExpressionParser();
        Expression exp = parser.parse(expression);
        int result = exp.interpret();
        System.out.println(expression + " = " + result);
    }
}