java计算器的核心算法

oneday做了计算器的界面，网上搜了下算法，但是搜不到具体的java代码，闲来无事，写了个，欢迎大家来喷！
* @author superGenius吴大仙＾＾！蛋疼仔
* 计算器算法的实现
   *定义两个堆栈，一个放置操作数，一个放置操作符
   *1.首先把得到的数学表达式转化成为逆波兰式 Reverse Polish Notation
   *  对于一个表达式，遇到数字便+入到新的逆波兰式，假如遇到的是操作符，首先比较其和操作符堆栈里面
   *  操作符的优先级，假如优先级较高，便加入到操作符堆栈中，or+入到逆波兰式中
   * 2.计算逆波兰式
   * 遍历波兰式，遇到数字便放入堆栈，遇到操作符，操作数堆栈弹出，执行相应的操作符操作，util...then ok;

import java.util.HashMap;
import java.util.Map;

import java.util.Stack;



public class CalculatorIn {
    private Stack<Double> operandStack=new Stack<Double>();//操作数堆栈
    private Stack<String> operatorStack=new Stack<String>();//操作符堆栈
    private String expression;//算数表达式
    private double result=0.0;//计算结果
    private Map<String,Integer> priorityMap=new HashMap<String,Integer>();//用于存储操作符优先级的Map
    //初始化优先级约定(可根据计算的复杂程度扩展)
    public CalculatorIn()
    {
        priorityMap.put("+",0);
        priorityMap.put("-",0);
        priorityMap.put("*", 1);
        priorityMap.put("/", 1);
       
    }
   
    public int getPriority(String op)//得到一个操作符的优先级
    {
        return priorityMap.get(op);
    }
   
    public boolean highPriority(String op)//判断操作符的优先级在堆栈里面是否最为高
    {
        int opPri=getPriority(op);//当前操作符的优先级
        if(!operatorStack.empty())
        {
        for(String s:operatorStack)
        {
            int priority=getPriority(s);
            if(opPri<priority)
                return false;
           
        }
        }
        return true;
    }
    //把表达式转化成逆波兰式
    public String expToIpn()
    {
        int index=0;
        int end=0;
        String Ipn="";
        for(int i=0;i<expression.length();i++)
        {
            String temps=String.valueOf(expression.charAt(i));
            if(temps.matches("[0-9.]"))//检查是否是数字
            {
                end++;
            }
            else
            {
                String tempOperand=expression.substring(index,end);//得到操作数
                Ipn+=tempOperand+",";
                String tempOperator=expression.substring(end,++end);//得到操作符
                if(tempOperator.equals("!"))//假如到表达式的最后将操作符 全部弹出
                    {
                    while(!operatorStack.empty())
                    {
                         Ipn+=operatorStack.pop()+",";
                     }
                    }
                 else
                 {
                if(highPriority(tempOperator))//优先级高的压入操作符堆栈
                    {
                    operatorStack.push(tempOperator);
                    }
                 else
                    {
                     while(!operatorStack.empty())//
                    {
                         Ipn+=operatorStack.pop()+",";
                     }
                    
                     operatorStack.push(tempOperator);
                    }
                //System.out.println(tempOperand+","+tempOperator);
                index=end;
            }
            }
           
        }
        return Ipn;
   
    }
    public double calculateIpn(String[] Ipn)//计算逆波兰式
    {
         
        for(int i=0;i<Ipn.length;i++)
        {
        //    System.out.println(Ipn[i]);
            if(Ipn[i].matches("^[0-9]+.?[0-9]*$"))//正则表达式判断是数字
            {
                operandStack.push(Double.parseDouble(Ipn[i]));
            }
                else
                {
                    popOperand(Ipn[i]);
                }
        }
        return result;
       
    }
    //遇到操作符时，弹出操作数，进行相应操作，并保村result
    public void popOperand(String operator)
    {
        double d1=operandStack.pop();
        double d2=operandStack.pop();
        System.out.println(d1+operator+d2);
        if(operator.equals("+"))
            result=d2+d1;
        if(operator.equals("-"))
            result=d2-d1;
        if(operator.equals("*"))
            result=d2*d1;
        if(operator.equals("/"))
            result=d2/d1;
//System.out.println(result);
            operandStack.push(result);
       
    }

    public Stack getOperandStack() {
        return operandStack;
    }
    public void setOperandStack(Stack operandStack) {
        this.operandStack = operandStack;
    }
    public Stack getOperatorStack() {
        return operatorStack;
    }
    public void setOperatorStack(Stack operatorStack) {
        this.operatorStack = operatorStack;
    }
    public String getexpression_r() {
        return expression;
    }
    public void setexpression_r(String expression) {
        this.expression = expression;
    }
    public double getResult() {
        return result;
    }
    public void setResult(double result) {
        this.result = result;
    }

    public static void main(String[] args)
    {
        CalculatorIn cal=new CalculatorIn();
        String exp="32+1*2*2/2*2-2/2!";
        cal.setexpression_r(exp);
        String[] Ipn=cal.expToIpn().split(",");
         for(int i=0;i<Ipn.length;i++)
        System.out.println(Ipn[i]);
        System.out.println(cal.calculateIpn(Ipn));
    }

}

评论

1 楼 lqvc2011 2013-12-16  

这个代码有时会出错，范例3×9-9-2×9,，lz可以解释一下吗