package com.liuzhen.systemExe;import java.util.Scanner;
import java.util.Stack;public class Main{//计算表达式的值public void getExpressionValue(String A){char[] arrayA = A.toCharArray();Stack<Integer> Value = new Stack<Integer>();      //存放运算数字及表达式计算结果Stack<Character> Operator =  new Stack<Character>();   //存放运算符for(int i = 0;i < A.length();i++){int temp = 0;if(arrayA[i] >= '0' && arrayA[i] <= '9'){temp = arrayA[i] - '0';i = i + 1;while(i < A.length() && arrayA[i] >= '0' && arrayA[i] <= '9'){temp = temp * 10 + (arrayA[i] - '0');i++;}i--;     //对应上面一句i = i+1;因为在for循环中有i++自增操作，若不执行此句，会导致i自增两次
                Value.push(temp);}else{if(Operator.empty()){Operator.push(arrayA[i]);}else{char temp1 = Operator.pop();   //进栈前，存放运算符栈中栈顶存放字符int judge = comparePriority(temp1,arrayA[i]);  //比较当前字符与栈顶字符优先级if(judge == 1){           //当前字符优先级小于栈顶字符int tempA = Value.pop();int tempB = Value.pop();int result = computeNumber(tempB,tempA,temp1);Value.push(result);Operator.push(arrayA[i]);}if(judge == 0){           //当前字符优先级大于栈顶字符
                        Operator.push(temp1);Operator.push(arrayA[i]);}if(judge == 2){  //字符')'遇到'('，刚好使得'('出栈System.out.println("'('刚好遇到')'");   //这种情况也应该不会出现，按照给定优先级，')'一般会先遇到+、-、*、/字符
                    }if(judge == 3){   //此时')'刚好准备进栈while(temp1 != '('){          //')'字符要等到第一个'('出栈才能结束循环//System.out.println(temp1);int tempA = Value.pop();int tempB = Value.pop();int result = computeNumber(tempB,tempA,temp1);Value.push(result);temp1 = Operator.pop();  }}if(judge == -1){    //此时，说明当前栈顶字符为')'，这是不存在的，因为遇到')'，按要求不让进栈System.out.println("出现栈顶有')'错误！！！");}}}}while(!Operator.empty() && !Value.empty()){   //此时，字符栈中还存在运算符的情况char temp1 = Operator.pop();int tempA = Value.pop();int tempB = Value.pop();int result = computeNumber(tempB,tempA,temp1);Value.push(result);}System.out.println(Value.pop());   //此时运算符栈为空，数字栈中只存在表达式计算最终结果
    }//计算a operator b的值，operator = {+,-,*,/}public int computeNumber(int a,int b,char operator){int result;switch(operator){case '+': result = a+b;break;case '-':result = a-b;break;case '*': result = a*b;break;case '/': result = a/b;break;        default:  result = 0;break;}return result;}//判断运算符a和b的优先级public int comparePriority(char a,char b){//使用二维数组表达运算符之间的优先级，行用字符a表示，列用字符b表示int[][] Value = {{1,1,0,0,0,3},{1,1,0,0,0,3},{1,1,1,1,0,3},{1,1,1,1,0,3},{0,0,0,0,0,2},{-1,-1,-1,-1,-1,-1}};int i = 0;int j = 0;if(a == '+')i = 0;if(a == '-')i = 1;if(a == '*')i = 2;if(a == '/')i = 3;if(a == '(')i = 4;if(a == ')')i = 5;if(b == '+')j = 0;if(b == '-')j = 1;if(b == '*')j = 2;if(b == '/')j = 3;if(b == '(')j = 4;if(b == ')')j = 5;return Value[i][j];}public static void main(String[] args){Main test = new Main(); Scanner in = new Scanner(System.in);System.out.println("请输入一个算法表达式：");String A = in.nextLine();test.getExpressionValue(A);}
}

请输入一个算法表达式：
1-2+3*(4-5)
-4请输入一个算法表达式：
1-2*((2+3)*2-(2+3))
-9请输入一个算法表达式：
1-2*((2+3)*(2+3))
-49