关于Java 设计模式 解释器模式 Interpreter

1、Expression.java

package com.ssm.cts.pattern.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);
}

2、VarExpression.java

package com.ssm.cts.pattern.interpreter;

import java.util.HashMap;

// 变量解析器，就是把变量和数值对应起来
public class VarExpression extends Expression {
  private String key;
  
  public VarExpression(String _key){
    this.key = _key;
  }
  
  public int interpreter(HashMap<String, Integer> var) {
    return var.get(this.key);
  }

}

3、Calculator.java

package com.ssm.cts.pattern.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);
  }
}

4、SymbolExpression.java

package com.ssm.cts.pattern.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;
  }

}

5、AddExpression.java

package com.ssm.cts.pattern.interpreter;

import java.util.HashMap;

public class AddExpression extends SymbolExpression {

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

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

}

6、SubExpression.java

package com.ssm.cts.pattern.interpreter;

import java.util.HashMap;

public class SubExpression extends SymbolExpression {

  public SubExpression(Expression _left, Expression _right) {
    super(_left, _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 int interpreter(HashMap<String, Integer> var) {
    return super.left.interpreter(var) - super.right.interpreter(var);
  }

}

7、Demo.java

package com.ssm.cts.pattern.interpreter;

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

public class Demo {

  // 运行四则运算
  public static void main(String[] args) throws IOException {
    String expStr = "a+b"; //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 != '-') {
        if (!map.containsKey(String.valueOf(ch))) { // 解决重复参数的问题
          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;
  }
}