算法训练 表达式计算

import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.Stack;  

    public class Main{   
        public static void main(String[] args){  
            Scanner input = new Scanner(System.in);
            String a = input.next();
            Stack<Integer> shu = new Stack<Integer>();
            Stack<Character> fu = new Stack<Character>();
            int index = 0;
            for(int i=0;i<a.length();i++){
                char temp = a.charAt(i);
                if(temp>=‘9‘||temp>=‘0‘){
                    index++;
                }else{
                    if(index!=0){
                        shu.push(Integer.parseInt(a.substring(i-index, i)));
                        index = 0;
                    }
                    if(fu.isEmpty()==true){
                        fu.push(temp);
                    }else if(temp==‘+‘||temp==‘-‘){
                        while(fu.size()!=0&&fu.peek()!=‘(‘){
                            int b1 = shu.pop();
                            int a1 = shu.pop();
                            shu.push(jisuan(a1,b1,fu.peek()));
                            fu.pop();
                        }
                            fu.push(temp);
                            
                    }else if(temp==‘*‘||temp==‘/‘){
                        if(fu.peek()!=‘(‘){
                            while(fu.peek()==‘*‘||fu.peek()==‘/‘){
                                int b1 = shu.pop();
                                int a1 = shu.pop();
                                shu.push(jisuan(a1,b1,fu.peek()));
                                fu.pop();
                                fu.push(temp);
                            }
                            fu.push(temp);
                        }
                        else{
                            fu.push(temp);
                        }
                    }
                    else if(temp==‘(‘){
                        fu.push(temp);
                    }else if(temp==‘)‘){
                        while(fu.peek()!=‘(‘){
                            if(fu.peek()==‘*‘||fu.peek()==‘/‘){
                                int b1 = shu.pop();
                                int a1 = shu.pop();
                                shu.push(jisuan(a1,b1,fu.peek()));
                                fu.pop();
                                continue;
                            }
                            if(fu.peek()==‘-‘||fu.peek()==‘+‘){
                                int b1 = shu.pop();
                                int a1 = shu.pop();
                                shu.push(jisuan(a1,b1,fu.peek()));
                                fu.pop();
                            }
                        }
                        fu.pop();
                    }
                } 
            
            }
            while(fu.size()!=0){
                int b1 = shu.pop();
                int a1 = shu.pop();
                shu.push(jisuan(a1,b1,fu.pop()));
            }
            System.out.println(shu.pop());
        }
        public static int jisuan(int a,int b,char c){
            int result=0;
            if(c==‘-‘){
                result = a-b;
            }
            if(c==‘+‘){
                result = a+b;
            }
            if(c==‘*‘){
                result = a*b;
            }
            if(c==‘/‘){
                result = a/b;
            }
            return result;
        }
 }