java - 使用堆栈进行后缀评估

Question

我正在尝试编写一种求解后缀方程的方法。对于前。

1 2 + 3 *

这 = 9

到目前为止，我收到了ArrayoutofboundsException。我认为问题出在我的 postFixEvaluation 方法中的 if(statement) 。

代码的第一部分是我正在谈论的需要帮助的地方。之后是我的其余代码。不确定你们是否需要阅读该内容。

public int PostfixEvaluate(String e) {
    String Operator = "";
    int number1;
    int number2;
    int result = 0;
    char c;
    number1 = 0;
    number2 = 0;

    for (int j = 0; j < e.length(); j++) {
        c = e.charAt(j);
        if (c == (Integer) (number1)) {
            s.push(c);
        } else {
            number1 = s.pop();
            number2 = s.pop();
            switch (c) {
                case '+':
                    result = number1 + number2;
                    break;
                case '-':
                    result = number1 - number2;
                    break;
                case '*':
                    result = number1 * number2;
                    break;
                case '/':
                    result = number1 / number2;
                    break;
                case '%':
                    result = number1 % number2;
                    break;
            }
        }
    }

    return result;
}

public static void main(String[] args) {
    Stacked st = new Stacked(100);
    String y = new String("(z * j)/(b * 8) ^2");
    String x = new String("10 3 + 9 *");
    TestingClass clas = new TestingClass(st);

    clas.test(y);
    //System.out.println(stacks.test(y));

    clas.PostfixEvaluate(x);
}

<小时/>

以下是可能相关的其余代码:

public class Stacked {

    int top;
    char stack[];
    int maxLen;

    public Stacked(int max) {
        top = 0;
        maxLen = max;
        stack = new char[maxLen];

    }

    public void push(int result) {
        top++;
        stack[top] = (char) result;

    }

    public int pop() {
        int x;
        x = stack[top];
        //top = top - 1;
        top--;
        return x;

    }

    public boolean isStackEmpty() {
        if (top == 0) {
            System.out.println("Stack is empty " + "Equation Good");
            return true;
        } else
            System.out.println("Equation is No good");
        return false;
    }

    public void reset() {

        top = -1;
    }

    public void showStack() {
        System.out.println(" ");
        System.out.println("Stack Contents...");
        for (int j = top; j > -1; j--) {
            System.out.println(stack[j]);
        }
        System.out.println(" ");
    }

    public void showStack0toTop() {
        System.out.println(" ");
        System.out.println("Stack Contents...");
        for (int j = 0; j >= top; j++) {
            System.out.println(stack[j]);
        }
        System.out.println(" ");
    }
}

Answer 1

您需要将操作结果推回堆栈。然后在末尾(当表达式字符串末尾时)弹出堆栈并返回值。

// excerpted, with odd bracket indentions unchanged.
for(int j = 0; j < e.length(); j++){
    c = e.charAt(j);
    if (c == (Integer)(number1)) {
        s.push(c); }
    else {
        number1 = s.pop();
        number2 = s.pop();
        switch(c) {
            case '+':
                result = number1 + number2;
                break;
            case '-':
                result = number1 - number2;
                break;
            case '*':
                result = number1 * number2;
                break;
            case '/':
                result = number1 / number2;
                break;
            case '%':
                result = number1 % number2;
                break;
            }
        s.push(result);  // <=== push here
        }
    }
}

return s.pop(); // <==== pop here