行为型模式-解释器模式

package behavior.pattern.intermediator.interpreter;

import java.util.HashMap;

public abstract class Expression {
    //解析公式和数值,其中var中的key值是是公式中的参数，value值是具体的数字
    public abstract int interpreter(HashMap<String,Integer> var);
      
}

package behavior.pattern.intermediator.interpreter;

public abstract class SymbolExpression extends Expression {

    protected Expression left;
    protected Expression right;

    // 所有的解析公式都应只关心自己左右两个表达式的结果

    public SymbolExpression(Expression _left, Expression _right) {
        this.left = _left;
        this.right = _right;
    }

}

package behavior.pattern.intermediator.interpreter;

import java.util.HashMap;

public class VarExpression extends Expression {

    private String key;

    public VarExpression(String _key) {
        this.key = _key;
    }

    // 从map中取之
    public int interpreter(HashMap<String, Integer> var) {
        return var.get(this.key);
    }
}

package behavior.pattern.intermediator.interpreter;

import java.util.HashMap;

public class AddExpression extends SymbolExpression {

    public AddExpression(Expression _left, Expression _right) {
        super(_left, _right);
    }

    // 把左右两个表达式运算的结果加起来

    public int interpreter(HashMap<String, Integer> var) {
        return super.left.interpreter(var) + super.right.interpreter(var);
    }

}

package behavior.pattern.intermediator.interpreter;

import java.util.HashMap;

public class SubExpression extends SymbolExpression {

    public SubExpression(Expression _left, Expression _right) {
        super(_left, _right);
    }

    // 左右两个表达式相减
    public int interpreter(HashMap<String, Integer> var) {
        return super.left.interpreter(var) - super.right.interpreter(var);
    }

}

package behavior.pattern.intermediator.interpreter;

import java.util.HashMap;
import java.util.Stack;

public class Calculator {
    // 定义的表达式
    private Expression expression;
    // 构造函数传参,并解析
    public Calculator(String expStr) {
        // 定义一个堆栈，安排运算的先后顺序
        Stack<Expression> stack = new Stack<Expression>();
        // 表达式拆分为字符数组
        char[] charArray = expStr.toCharArray();

        // 运算
        Expression left = null;
        Expression right = null;

        for (int i = 0; i < charArray.length; i++) {
            switch (charArray[i]) {
            case ‘+‘: // 加法
                // 加法结果放到堆栈中
                left = stack.pop();
                right = new VarExpression(String.valueOf(charArray[++i]));
                stack.push(new AddExpression(left, right));
                break;
            case ‘-‘:
                left = stack.pop();
                right = new VarExpression(String.valueOf(charArray[++i]));
                stack.push(new SubExpression(left, right));
                break;
            default: // 公式中的变量
                stack.push(new VarExpression(String.valueOf(charArray[i])));
            }
        }
        // 把运算结果抛出来
        this.expression = stack.pop();
    }

    // 开始运算

    public int run(HashMap<String, Integer> var) {
        return this.expression.interpreter(var);
    }
}

package behavior.pattern.intermediator.interpreter;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;

public class Client {
    // 运行四则运算

    public static void main(String[] args) throws IOException {
        String expStr = getExpStr();
        // 赋值
        HashMap<String, Integer> var = getValue(expStr);
        Calculator cal = new Calculator(expStr);
        System.out.println("运算结果为：" + expStr + "=" + cal.run(var));
    }

    // 获得表达式

    public static String getExpStr() throws IOException {
        System.out.print("请输入表达式：");
        return (new BufferedReader(new InputStreamReader(System.in))).readLine();
    }

    // 获得值映射
    public static HashMap<String, Integer> getValue(String exprStr) throws IOException {
        HashMap<String, Integer> map = new HashMap<String, Integer>();
        // 解析有几个参数要传递
        for (char ch : exprStr.toCharArray()) {
            if (ch != ‘+‘ && ch != ‘-‘) {
                // 解决重复参数的问题
                if (!map.containsKey(String.valueOf(ch))) {
                    System.out.print("请输入" + ch + "的值:");
                    String in = (new BufferedReader(new InputStreamReader(System.in))).readLine();
                    map.put(String.valueOf(ch), Integer.valueOf(in));
                }
            }
        }

        return map;
    }
}