ExpressionEvaluator.java

import java.util.ArrayDeque;
import java.util.Deque;

public class ExpressionEvaluator {
    public double stringss(String expression) {
        String cleanedExpression = expression.replaceAll("\\s+", "");
        String[] tokens = cleanedExpression.split("(?<=\\D)|(?=\\D)");

        Deque<Double> operandStack = new ArrayDeque<>();
        Deque<Character> operatorStack = new ArrayDeque<>();

        for (String token : tokens) {
            if (isNumeric(token)) {
                double operand = Double.parseDouble(token);
                operandStack.push(operand);
            } else if (isOperator(token.charAt(0))) {
                char c = token.charAt(0);
                while (!operatorStack.isEmpty() && hasPrecedence(c, operatorStack.peek())) {
                    performOperation(operandStack, operatorStack);
                }
                operatorStack.push(c);
            } else if (token.equals("(")) {
                operatorStack.push('(');
            } else if (token.equals(")")) {
                while (!operatorStack.isEmpty() && operatorStack.peek() != '(') {
                    performOperation(operandStack, operatorStack);
                }
                operatorStack.pop();
            }
        }

        while (!operatorStack.isEmpty()) {
            performOperation(operandStack, operatorStack);
        }

        return operandStack.pop();
    }

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

    public boolean hasPrecedence(char op1, char op2) {
        if (op2 == '(' || op2 == ')') {
            return false;
        }
        return (op1 == '*' || op1 == '/') && (op2 == '+' || op2 == '-');
    }

    public void performOperation(Deque<Double> operandStack, Deque<Character> operatorStack) {
        double operand2 = operandStack.pop();
        double operand1 = operandStack.pop();
        char operator = operatorStack.pop();
        double result = 0.0;

        switch (operator) {
            case '+':
                result = operand1 + operand2;
                break;
            case '-':
                result = operand1 - operand2;
                break;
            case '*':
                result = operand1 * operand2;
                break;
            case '/':
                result = operand1 / operand2;
                break;
        }

        operandStack.push(result);
    }

    public boolean isNumeric(String str) {
        return str.matches("-?\\d+(\\.\\d+)?");
    }
}