Meal WaitPerson and Chef

import java.util.Stack;
import java.util.regex.Pattern;
import java.util.regex.Matcher;
import java.util.Map;
import java.util.HashMap;
public class ArithmeticExpressionEvaluation {
    private static Stack<Character> theStack;
    private static char charKey=(char)97;
    private  static Map<Character,String>  hashMap=new HashMap<Character,String>();
    private static String result;
    public static void main(String[] args) {
        if(args.length<1) {
            System.out.println(" please enter the input arithmetic expression string  that needs to be evaluated."+
                               "the  legal operators include '+', '-','*' and '/' ,and you can also add '(' and ')' ."+
                               "all numbers must above zero, the program doesn't support negative values now "
                              );
            System.exit(0);
        }
        System.out.println("the original input is :"+args[0]);
        String internalStr=processBeforeEvaluation(args[0]);
        System.out.println("the internal expression is :"+internalStr);
        String postfixStr= translateToPostfixExpression(internalStr);
        System.out.println("the postfix expression is :"+postfixStr);
        double result=evaluatePostfixExpression(postfixStr);
        System.out.println("the final result is :"+result);
    }
    private static String processBeforeEvaluation(String input) {
        Matcher legal=Pattern.compile("[^0-9.*+/\\()-]").matcher(input);
        if(legal.find()) {
            System.out.println("Please enter legal arithmetic expression string.");
            System.exit(0);
        }
        StringBuffer sbuf = new StringBuffer();
        Matcher m=Pattern.compile("\\d+(\\.\\d+)?").matcher(input);
        while(m.find()) {
            String temp=m.group(0);
            hashMap.put(charKey,temp);
            m.appendReplacement(sbuf,charKey+"");
            charKey=(char)(charKey+1);
        }
        m.appendTail(sbuf);
        return sbuf.toString();
    }


    private static String translateToPostfixExpression(String input) {
        theStack=new Stack<Character>();
        result="";
        for(int j=0; j<input.length(); j++) {
            char ch=input.charAt(j);
            switch(ch) {
            case '+':
            case '-':
            case '*':
            case '/':
                gotOper(ch);
                break;
            case '(':
                theStack.push(ch);
                break;
            case ')':
                gotParen(ch);
                break;
            default :
                result+=ch;
                break;
            }  //end switch
        } //end for loop
        while(!theStack.empty()) {
            result+=theStack.pop();
        }
        return result;
    }
    private static void gotOper(char opThis) {
        while(!theStack.empty()) {
            char opTop=theStack.pop();
            if(opTop=='(') {
                theStack.push(opTop);
                break;
            } else {
                if(opThis=='*'||opThis=='/') {   //如果是本次是乘除,棧裏最多可彈出一個乘號
                    if(opTop=='+'||opTop=='-') {
                        theStack.push(opTop);
                    } else {
                        result+=opTop;
                    }
                    break;
                } else {            //如果是本次是加減,棧裏最多可彈出一次乘除,再加一次加減
                    result+=opTop;
                }
            } //end else
        }//end while
        theStack.push(opThis);
    }//end gotOper()



    private static void gotParen(char ch) {
        while(!theStack.empty()) {
            char chx=theStack.pop();
            if(chx=='(')
                break;
            else
                result+=chx;
        } //end while
    }


    private static double evaluatePostfixExpression(String input) {
        System.out.println("the content of the hashMap is :"+hashMap);
        char ch;
        double num1,num2,interAns=0;
        String str1,str2;
        theStack=new Stack<Character>(); //重置棧,後綴表達式求值是將數字放入棧中
        try {
            for(int j=0; j<input.length(); j++) {
                ch=input.charAt(j);
                if(ch>=97) {  //j代表一個double型的數字
                    theStack.push(ch);
                } else {
                    str2 =hashMap.get(theStack.pop());
                    str1=hashMap.get(theStack.pop());
                    num2=Double.parseDouble(str2);
                    num1=Double.parseDouble(str1);
                    switch(ch) {
                    case '+':
                        interAns=num1+num2;
                        break;
                    case '-':
                        interAns=num1-num2;
                        break;
                    case '*':
                        interAns=num1*num2;
                        break;
                    case '/':
                        interAns=num1/num2;
                        break;
                    default :
                        interAns=0;
                        break;
                    } //end switch
                    hashMap.put(charKey,interAns+"");
                    theStack.push(charKey);
                    charKey=(char)(charKey+1);
                } //end else
            } //end for loop
            str1=hashMap.get(theStack.pop());
            interAns=Double.parseDouble(str1);
        } catch(Exception e) {
            System.out.println("please enter legal numbers!");
            e.printStackTrace();
        }
        return interAns;
    }





}