添加一个 Java 字符串并将其转换为整数并得到其和

Question

我需要你的帮助。我需要得到上述等式的总和，我一直坚持连接过程，这将使我添加等式的结果。

String eq = "15+5cdf-45+90$%#@";
StringBuffer s = new StringBuffer(eq);

for (int i = 0; i < s.length(); i++) {
    if (s.charAt(i) >= 48 && s.charAt(i) <= 57 || s.charAt(i) == '+' || s.charAt(i) == '-') {

    } else {
        s.deleteCharAt(i);
        i--;
    }

}

System.out.println(s);  

String a = new String (s);

//15+5-45+90

String y = "";
String z = "";  

for (int x = 0; x < a.length(); ++x) {

    if (a.charAt(x) == '+'){
        a = a.substring(0, x);
        y = a;
    } 

    z = y.concat(y);
}

System.out.println(z);

Answer 1

你不需要做你正在做的大部分事情。

public static void main(String[] args) {
    String eq = "15+5cdf-45+90$%#@";
    long sum = eval(eq);
    System.out.println("sum: " + sum);
}

private static long eval(String eq) {
    int sign = +1;
    long num = 0, sum = 0;
    for (int i = 0; i < eq.length(); i++) {
        char ch = eq.charAt(i);
        if (ch >= '0' && ch <= '9') {
            num = num * 10 + ch - '0';
        } else if (ch == '-' || ch == '+') {
            sum += sign * num;
            sign = ch == '-' ? -1 : +1;
            num = 0;
        }
    }
    sum += sign * num;
    return sum;
}

打印

如您所见，作为解析器计算忽略意外字符的表达式所需的一切。

注意：eval 不创建任何对象。

Answer 2

public class Equation {

    public static void main(String[] args) {
        String eq = "15+5cdf-45+90$%#@";

        StringBuffer s = new StringBuffer (eq);

        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) >= 48 && s.charAt(i) <= 57 || s.charAt(i) == '+'
                    || s.charAt(i) == '-') {
            } else {
                s.deleteCharAt(i);
                i--;
            }

        }
        System.out.println(s);

        String a = new String(s);

        // 15+5-45+90
        String term = "";
        char previousOperator = '+';
        long sum = 0;
        boolean weHavePreviousTerm = false;

        for (int x = 0; x < a.length(); x++) {
//          if we got to a new operator
            if (a.charAt(x) == '+' || a.charAt(x) == '-') {
                if (weHavePreviousTerm) {
                    int previousTermValue = Integer.parseInt(term);
                    if (previousOperator == '-') {
                        previousTermValue *= -1;
                    }
                    System.out.println("Adding " + previousTermValue);
                    sum += previousTermValue;
                }
                previousOperator = a.charAt(x);
//              reset term buffer
                term = "";
            }
            else {
                term += a.charAt(x);
                weHavePreviousTerm = true;
            }
        }

//      do the last operation
//      if the last term didn't get reset, means we still have an operation left to do
        if (term.length()  > 0) {
            int previousTermValue = Integer.parseInt(term);
            if (previousOperator == '-') {
                previousTermValue *= -1;
            }
            System.out.println("Adding " + previousTermValue);
            sum += previousTermValue;
        }

        System.out.println(sum);
    }
}

添加一个 Java 字符串并将其转换为整数并得到其和

Adding a Java Strings and convert it into integer and get its sum

java

stringbuffer