کالکشن ها در جاوا: آموزش کار با Stack + مثال های کاربردی

Stack<String> cities = new Stack<>();

cities.push("Tehran");
cities.push("Arak");
cities.push("Isfahan");
cities.push("Tabriz");
cities.push("Mashhad");

System.out.println("Displaying cities: ");

while(!cities.isEmpty())
   System.out.print(cities.pop() + " ");

System.out.println();
        
        

public class EvaluateExpression {

     public double evaluateExpression(String expression) {

        Stack<Double> operands = new Stack<>();
        Stack<Character> operators = new Stack<>();

        expression = expression.trim(); //remove every space in expression
        expression = insertBlanks(expression);

        String[] tokens = expression.split("\\s");

        for (String token : tokens) {

            if (!token.isEmpty()) {

                if (token.charAt(0) == '+' || token.charAt(0) == '-') {

                    while (
                            !operators.isEmpty() && (operators.peek() == '+' || operators.peek() == '-' || operators.peek() == '*' || operators.peek() == '/')
                    ) {
                        processAnOperation(operators, operands);
                    }

                    operators.push(token.charAt(0));

                } else if (token.charAt(0) == '*' || token.charAt(0) == '/') {

                    while (!operators.isEmpty() && (operators.peek() == '*' || operators.peek() == '/')) {
                        processAnOperation(operators, operands);
                    }

                    operators.push(token.charAt(0));

                } else if (token.charAt(0) == '(') {

                    operators.push('(');

                } else if (token.charAt(0) == ')') {

                    while (operators.peek() != '(') {
                        processAnOperation(operators, operands);
                    }
                    operators.pop();

                } else {
                    operands.push(Double.parseDouble(token));
                }
            }
        }

        while (!operators.isEmpty())
            processAnOperation(operators, operands);

        return operands.pop();
    }


    private static void processAnOperation(Stack<Character> operators, Stack<Double> operands) {
        char op = operators.pop();
        double operand0 = operands.pop();
        double operand1 = operands.pop();

        switch (op) {
            case '*' -> operands.push(operand1 * operand0);
            case '/' -> operands.push(operand1 / operand0);
            case '-' -> operands.push(operand1 - operand0);
            case '+' -> operands.push(operand1 + operand0);
        }
    }

    private static String insertBlanks(String s) {
        StringBuilder result = new StringBuilder();

        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            if (ch == '+' || ch == '-' || ch == '*' || ch == '/' || ch == '(' || ch == ')')
                result.append(" ").append(ch).append(" ");
            else result.append(ch);
        }

        return result.toString();
    }
}