Question

我有一个名为questions String类型的数组，存储在问题中。我想将questionArray[0]转换为int。我使用以下语句来做到这一点。

int aa = Integer.parseInt(questionArray[0]);

但是当我实现这个语句时，当我运行应用程序时，我得到一个错误：invalid int: "10-4"。请注意，10-4可以是任意随机算术表达式，因为它是一个随机问题游戏。例如：9+1，10/5等。

Answer 1

"10-4"不是一个简单的整数，它是一个计算，因此将其解析为int将不会产生任何结果..

你必须解析你的字符串..

int aa = evaluteQuestion(questionArray[0]);

实际的魔法发生在这里：

public static int evaluteQuestion(String question) {
    Scanner sc = new Scanner(question);

    // get the next number from the scanner
    int firstValue = Integer.parseInt(sc.findInLine("[0-9]*"));

    // get everything which follows and is not a number (might contain white spaces)
    String operator = sc.findInLine("[^0-9]*").trim();
    int secondValue = Integer.parseInt(sc.findInLine("[0-9]*"));
    switch (operator){
        case "+":
            return firstValue + secondValue;
        case "-":
            return firstValue - secondValue;
        case "/":
            return firstValue / secondValue;
        case "*":
            return firstValue * secondValue;
        case "%":
            return firstValue % secondValue;
        // todo: add additional operators as needed..
        default:
            throw new RuntimeException("unknown operator: "+operator);
    }
}

如果表达式中有更多部分，则可能需要将上面的代码放入循环中。但请注意操作顺序。如果你想为任何表达式实现适当的解析器，事情可能会变得有点毛茸茸

Answer 2

它比解析String有点复杂，因为它有一个算术符号，它可以是任何东西。所以，让我们一步一步地讨论它：

//Lets say you have a string like this
questionArray[0] = "10+4";
//Lets find the Arithmetic sign first in the String
String sign = null;

Pattern regex = Pattern.compile("[+*/]|(?<=\\s)-");
Matcher matcher = regex.matcher(questionArray[0]);
    while(matcher.find()) {
       sign = matcher.group().trim();  //Store that Arithmetic sign here.       
    }

String [] parts = questionArray[0].split("[+*/]|(?<=\\s)-"); //Now break up the string using this regex. 
                                              //This regex will find whatever Arithmetic sign 
                                              //there is inside this String and store the result 
                                              //in parts array.

int firstNumber = Integer.parseInt(parts[0]); //The first number in the String
int secondNumber = Integer.parseInt(parts[1]);//The second number in the String

//a simple if-else statements that will help us find the final answer.
int result = 0;
if (sign.equals("+")){
    result = firstNumber + secondNumber;
} else if (sign.equals("-")) {
    result = firstNumber - secondNumber;
} else if(sign.equals("*")) {    
    result = firstNumber * secondNumber;
} else if (sign.equals("/")){
    result = firstNumber / secondNumber;
} else {
    System.out.println("unknown operation");
}

System.out.println(result);

如何将包含数学表达式的字符串转换为整数？

2 个答案: