java - BODMAS系统的加减法

Question

我一直在构建一个简单的公式计算器，并且一直在加减法中。正如您应该知道的，在计算方程时，您遵循优先级的算术规则，即括号、顺序:幂函数、除法、乘法、加法和减法。问题是加法和减法的优先级相同，因此您可以从左到右阅读。到目前为止，这是我的代码:

{
ArrayList<String> equation = java.util.Arrays.asList({"2","-","2","+","5"});

  while(equation.contains("+")){
          addMe(equation);
  }
  while(equation.contains("-")){
          minusMe(equation);            
  }
}

public static void addMe(ArrayList<String> numberList){
 for (int i = 0, n = numberList.size(); i < n; i++) { 
   String value = (String) numberList.get(i); 
   if(value.equals("+")){

    String wordBefore = (String) numberList.get(i-1);
    String wordAfter = (String) numberList.get(i+1);
    System.out.println("This is the word before " + wordBefore);
    System.out.println("This is the word after " + wordAfter);
    double doubleFromBefore = Double.parseDouble(wordBefore);
    double doubleFromAfter = Double.parseDouble(wordAfter);
    double answer = doubleFromBefore + doubleFromAfter;
    System.out.println("This is the answer: " + answer);
    String stringAnswer = String.valueOf(answer);
    String newNum2 = value.replace(value, stringAnswer);
    numberList.set(i,newNum2);
    numberList.remove(i-1);
    numberList.remove(i);
    break;
  }
 }   
}

minusMe 方法与 addMe 方法完全相同，只是在相关地方加了“-”。我遇到的问题是让方程一次从左到右读取一项，然后执行加法或减法。理想情况下，我认为我需要将我的 2 while 循环与迭代器结合起来，以解决问题，但我的尝试没有奏效。知道这是否会解决我的问题吗？如果是这样，请提供修改后的循环。

问候

Answer 1

看看这个

java.uti.ArrayList<String> equation = java.util.Arrays.asList({"2","-","2","+","5"});
java.util.Iterator<String> equIterator = equation.iterator();
int result = 0;
int multiplier = 1;
while(equIterator.hasNext()){
     String operandOrOperator = equIterator.next();
     if(operandOrOperator.equals("+")){
          multiplier=1;
     }else if(operandOrOperator.equals("-")){
          multiplier=-1;
     }else if(operandOrOperator.equals("*")){
          result*=Integer.parseInt(equIterator.next()); // Assuming that next element will be there always after operator.
     }else{
          result+=(multiplier * Integer.parseInt(operandOrOperator));
     }
}
System.out.println("Final result : " + result);