package 表達式求值;import java.util.Stack;/* * 中序表達式求值實現 */public class CenterExpression { public double evaluate(String expression){ //傳入中序表達式  char [] ex = expression.toCharArray();  Stack<Double> num = new Stack<>();  Stack<Character> ops = new Stack<>();  for(int i = 0; i < ex.length; i++){  //循環將表達式依次入棧   char c = ex[i];   if(c < '9' && c > '0'){    num.push(Double.parseDouble(Character.toString(c)));   }   else if(c == '('){    ops.push('(');   }   else if(c == ')'){    while(true){     char op = ops.pop();     if(op == '('){      break;     }     else{      switch(op){      case '+':num.push(num.pop()+num.pop());break;      case '-':num.push(num.pop()-num.pop());break;      case '*':num.push(num.pop()*num.pop());break;      case '/':num.push(num.pop()/num.pop());break;      default:break;      }     }    }   }   else if(ops.empty() && (c == '+' || c == '-' || c == '*' || c == '/')){    ops.push(c);   }   else if(!ops.isEmpty() && (c == '+' || c == '-' || c == '*' || c == '/')){    char op =ops.peek();    while((op == '*' || op == '/') && (c == '+' || c == '-')){     op = ops.pop();     switch(op){     case '+':num.push(num.pop()+num.pop());break;     case '-':num.push(num.pop()-num.pop());break;     case '*':num.push(num.pop()*num.pop());break;     case '/':num.push(num.pop()/num.pop());break;     default:break;     }     if(ops.isEmpty()){      break;     }     else{      op = ops.peek();     }    }    ops.push(c);   }  }  while(!ops.isEmpty()){  //處理剩余可以按計算機掃描順序處理的表達式   char op =ops.pop();   switch(op){   case '+':num.push(num.pop()+num.pop());break;   case '-':num.push(num.pop()-num.pop());break;   case '*':num.push(num.pop()*num.pop());break;   case '/':num.push(num.pop()/num.pop());break;   default:break;   }  }  return num.pop(); } public static void main(String [] args){  CenterExpression exp = new CenterExpression();  System.out.println(exp.evaluate("1*2+5*3")); }}