/**
 * 解釋器抽象類表達(dá)式，通過(guò)hashMap鍵值對(duì)，可以獲取到變量的值
 */
public abstract class Expression {
    /**
     * a + b - c
     * 解釋公式和數(shù)值，key就是公式（表達(dá)式） 參數(shù)[a,b,c],value就是具體值
     * HashMap{a=10,b=20}
     * @param var
     */
    public abstract int interpreter(HashMap<String, Integer> var);
}

package com.mayun.study.designpattern.interpreter;
 
import java.util.HashMap;
 
/**
 * 變量的解釋器
 */
public class VarExpression extends Expression {
    private String key;// key = a,key =b ,key = c
 
    public VarExpression(String key) {
        this.key = key;
    }
 
    /**
     *
     * @param var 就是{a=10,b=20}的一個(gè)HashMap
     * @return 根據(jù)變量名稱，返回對(duì)應(yīng)值
     */
    @Override
    public int interpreter(HashMap<String, Integer> var) {
        return var.get(this.key);
    }
}

package com.mayun.study.designpattern.interpreter;
 
import java.util.HashMap;
 
/**
 * 抽象運(yùn)算符號(hào)解釋器，這里，每個(gè)運(yùn)算符號(hào)都只和自由左右兩個(gè)數(shù)字有關(guān)系
 * 但左右兩個(gè)數(shù)字有可能也是一個(gè)解析的結(jié)果，無(wú)論何種類型，都是Expression類的實(shí)現(xiàn)類
 *
 */
public class SymbolExpression extends Expression {
    protected Expression left;
    protected Expression right;
 
    public SymbolExpression(Expression left, Expression right) {
 
        this.left = left;
        this.right = right;
    }
 
    /**
     * 因?yàn)?SymbolExpression 是讓其子類實(shí)現(xiàn)的，因此interpreter 是一個(gè)默認(rèn)實(shí)現(xiàn)
     * @param var
     * @return
     */
    @Override
    public int interpreter(HashMap<String, Integer> var) {
        return 0;
    }
}

package com.mayun.study.designpattern.interpreter;
 
import java.util.HashMap;
 
/**
 * 加法解釋器
 */
public class AddExpression extends SymbolExpression {
    public AddExpression(Expression left, Expression right) {
        super(left, right);
    }
 
    /**
     * 處理相加
     * @param var 仍然是{a=10,b=20}
     * @return  返回left表達(dá)式對(duì)應(yīng)的值 a =10 與右表達(dá)式對(duì)于寧的值b=20
     */
    @Override
    public int interpreter(HashMap<String, Integer> var) {
        return super.left.interpreter(var) + super.right.interpreter(var);
    }
}

 
import java.util.HashMap;
 
/**
 * 減法解釋器
 */
public class SubExpression extends SymbolExpression {
    public SubExpression(Expression left, Expression right) {
        super(left, right);
    }
 
    /**
     * 求出左右兩表達(dá)式相減的值
     * @param var
     * @return
     */
    @Override
    public int interpreter(HashMap<String, Integer> var) {
        return super.left.interpreter(var) - super.right.interpreter(var);
    }
}

package com.mayun.study.designpattern.interpreter;
 
import java.util.HashMap;
import java.util.Stack;
 
/**
 * 計(jì)算器類
 */
public class Calculator {
 
    //定義表達(dá)式
    private Expression expression;
 
    //構(gòu)造函數(shù)傳參，并解析
    public Calculator(String expStr) { // expStr = a+b
        //安排運(yùn)算的先后順序
        Stack<Expression> stack = new Stack<>();
        //表達(dá)式拆分成字符數(shù)組
        char[] charArray = expStr.toCharArray();
 
        Expression left = null;
        Expression right = null;
        //遍歷字符數(shù)組，即遍歷[a,+,b]
        //針對(duì)不同的情況，做處理
        for (int i = 0; i < charArray.length; i++) {
            switch (charArray[i]) {
                case '+':
                    left = stack.pop();//從stack中取出left
                    right = new VarExpression(String.valueOf(charArray[++i]));//取出右表達(dá)式“b”
                    stack.push(new AddExpression(left, right));//然后根據(jù)得到的left和right構(gòu)建AddExpression加入到stack
                    break;
                case '-':
                    left = stack.pop();
                    right = new VarExpression(String.valueOf(charArray[++i]));
                    stack.push(new SubExpression(left, right));
                    break;
                default:
                    //如果是一個(gè)Var ，就創(chuàng)建要給VarExpression 對(duì)象，并push到stack中
                    stack.push(new VarExpression(String.valueOf(charArray[i])));
                    break;
            }
        }
        //當(dāng)遍歷完整個(gè)charArray數(shù)組后，stack就得到最后的Expression
        this.expression = stack.pop();
    }
 
    public int run(HashMap<String, Integer> var) {
        //最后將表達(dá)式和var綁定 var ={a=10,b=20},
        // 然后傳遞給expression的interpreter進(jìn)行解釋執(zhí)行
        return this.expression.interpreter(var);
    }
 
}

package com.mayun.study.designpattern.interpreter;
 
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;
 
/**
 * 解釋器測(cè)試類
 */
public class Client {
    public static void main(String[] args) throws IOException {
        String expStr = getExpStr();//a +b\
        HashMap<String, Integer> var = getValue(expStr);//var {a=10,b=20}
        Calculator calculator = new Calculator(expStr);
        System.out.println("運(yùn)算結(jié)果：" + expStr + "=" + calculator.run(var));
    }
    //獲得表達(dá)式
    public static String getExpStr() throws IOException{
        System.out.println("請(qǐng)輸入表達(dá)式");
        return (new BufferedReader(new InputStreamReader(System.in))).readLine();
 
    }
    //獲得值映射
    public static HashMap<String,Integer> getValue(String expStr) throws IOException{
        HashMap<String, Integer> map = new HashMap<>();
        for (char ch : expStr.toCharArray()) {
            if (ch != '+' && ch != '-') {
                if (!map.containsKey(String.valueOf(ch))) {
                    System.out.print("請(qǐng)輸入" + String.valueOf(ch) + "的值：");
                    String in = (new BufferedReader(new InputStreamReader(System.in))).readLine();
                    map.put(String.valueOf(ch), Integer.valueOf(in));
                }
            }
        }
 
        return map;
    }
}