java算数表达式求值

Java中可以通过栈来实现算数表达式的求值。

具体步骤如下：

1. 创建两个栈，一个用来存储数字，一个用来存储操作符。

2. 将算数表达式转换为后缀表达式。

3. 遍历后缀表达式，如果是数字，则将其入数字栈，如果是操作符，则从数字栈中弹出两个数字进行计算，并将结果压入数字栈。

4. 最终数字栈中的唯一元素即为表达式的值。

下面是一个简单的示例代码：

import java.util.Stack;

public class ArithmeticExpressionEvaluation {
    public static int evaluate(String expression) {
        Stack<Integer> numbers = new Stack<>();
        Stack<Character> operators = new Stack<>();

        for (int i = 0; i < expression.length(); i++) {
            char c = expression.charAt(i);

            if (Character.isDigit(c)) {
                int num = 0;
                while (Character.isDigit(c)) {
                    num = num * 10 + (c - '0');
                    i++;
                    c = expression.charAt(i);
                }
                i--;
                numbers.push(num);
            } else if (c == '(') {
                operators.push(c);
            } else if (c == ')') {
                while (operators.peek() != '(') {
                    int num2 = numbers.pop();
                    int num1 = numbers.pop();
                    char op = operators.pop();
                    int result = calculate(num1, num2, op);
                    numbers.push(result);
                }
                operators.pop();
            } else if (isOperator(c)) {
                while (!operators.isEmpty() && precedence(operators.peek()) >= precedence(c)) {
                    int num2 = numbers.pop();
                    int num1 = numbers.pop();
                    char op = operators.pop();
                    int result = calculate(num1, num2, op);
                    numbers.push(result);
                }
                operators.push(c);
            }
        }

        while (!operators.isEmpty()) {
            int num2 = numbers.pop();
            int num1 = numbers.pop();
            char op = operators.pop();
            int result = calculate(num1, num2, op);
            numbers.push(result);
        }

        return numbers.pop();
    }

    private static int calculate(int num1, int num2, char op) {
        switch (op) {
            case '+':
                return num1 + num2;
            case '-':
                return num1 - num2;
            case '*':
                return num1 * num2;
            case '/':
                return num1 / num2;
            default:
                return 0;
        }
    }

    private static boolean isOperator(char c) {
        return c == '+' || c == '-' || c == '*' || c == '/';
    }

    private static int precedence(char op) {
        if (op == '*' || op == '/') {
            return 2;
        } else if (op == '+' || op == '-') {
            return 1;
        } else {
            return 0;
        }
    }

    public static void main(String[] args) {
        String expression = "5 + ((1 + 2) * 4) - 3";
        int result = evaluate(expression);
        System.out.println(result); // Output: 14
    }
}