Calculator.java

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.SystemColor;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.util.ArrayList;
import java.util.Stack;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingConstants;
import javax.swing.UIManager;
import javax.swing.border.BevelBorder;

public class Calculator {

    JFrame frmCalculator;
    String result = "", expression = "";
    ArrayList<String> token = new ArrayList<String>();

    boolean num = false;
    boolean dot = false;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    Calculator window = new Calculator();
                    window.frmCalculator.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    Calculator() {
        initialize();
    }

    int precedence(String x) {
        int p = 10;
        switch (x) {
            case "+":
                p = 1;
                break;
            case "-":
                p = 2;
                break;
            case "x":
                p = 3;
                break;
            case "/":
                p = 4;
                break;
            case "^":
                p = 6;
                break;
            case "!":
                p = 7;
                break;
        }

        return p;
    }

    // operator checking
    private boolean isoperator(String x) {
        if (x.equals("+") || x.equals("-") || x.equals("x") || x.equals("/") || x.equals("sqrt") || x.equals("^")
                || x.equals("!") || x.equals("sin") || x.equals("cos") || x.equals("tan") || x.equals("ln")
                || x.equals("log"))
            return true;
        else
            return false;
    }

    private String infixTopostfix() {
        Stack<String> s = new Stack<String>();
        String y;
        int flag;
        String p = "";
        token.add(")");
        s.push("(");
        for (String i : token) {
            if (i.equals("(")) {
                s.push(i);
            } else if (i.equals(")")) {
                y = s.pop();
                while (!y.equals("(")) {
                    p = p + y + ",";
                    y = s.pop();
                }
            } else if (isoperator(i)) {
                y = s.pop();
                flag = 0;
                if (isoperator(y) && precedence(y) > precedence(i)) {
                    p = p + y + ",";
                    flag = 1;
                }
                if (flag == 0)
                    s.push(y);

                s.push(i);
            } else {
                p = p + i + ",";
            }
        }
        while (!s.empty()) {
            y = s.pop();
            if (!y.equals("(") && !y.equals(")")) {
                p += y + ",";
            }
        }
        return p;
    }

    // factorial method
    private double factorial(double y) {
        double fact = 1;
        if (y == 0 || y == 1) {
            fact = 1;
        } else {
            for (int i = 2; i <= y; i++) {
                fact *= i;
            }
        }
        return fact;
    }

    // for actual calculation with binary operators
    private double calculate(double x, double y, String c) {
        double res = 0;
        switch (c) {
            case "-":
                res = x - y;
                break;
            case "+":
                res = x + y;
                break;
            case "x":
                res = x * y;
                break;
            case "/":
                res = x / y;
                break;
            case "^":
                res = Math.pow(x, y);
                break;
            default:
                res = 0;
        }
        return res;
    }

    // calculation with unary operators
    private double calculate(double y, String c) {
        double res = 0;
        switch (c) {
            case "log":
                res = Math.log10(y);
                break;
            case "sin":
                res = Math.sin(y);
                break;
            case "cos":
                res = Math.cos(y);
                break;
            case "tan":
                res = Math.tan(y);
                break;
            case "ln":
                res = Math.log(y);
                break;
            case "sqrt":
                res = Math.sqrt(y);
                break;
            case "!":
                res = factorial(y);
                break;
        }
        return res;
    }

    private double Eval(String p) {
        String tokens[] = p.split(",");
        ArrayList<String> token2 = new ArrayList<String>();
        for (int i = 0; i < tokens.length; i++) {
            if (!tokens[i].equals("") && !tokens[i].equals(" ") && !tokens[i].equals("\n") && !tokens[i].equals("  ")) {
                token2.add(tokens[i]); // tokens from post fix form p actual tokens for calculation
            }
        }

        Stack<Double> s = new Stack<Double>();
        double x, y;
        for (String i : token2) {
            if (isoperator(i)) {
                // if it is unary operator or function
                if (i.equals("sin") || i.equals("cos") || i.equals("tan") || i.equals("log") || i.equals("ln")
                        || i.equals("sqrt") || i.equals("!")) {
                    y = s.pop();
                    s.push(calculate(y, i));
                } else {
                    // for binary operators
                    y = s.pop();
                    x = s.pop();
                    s.push(calculate(x, y, i));
                }
            } else {
                if (i.equals("pi"))
                    s.push(Math.PI);
                else if (i.equals("e"))
                    s.push(Math.E);
                else
                    s.push(Double.valueOf(i));
            }
        }
        double res = 1;
        while (!s.empty()) {
            res *= s.pop();
        }
        return res; // final result
    }

    // actual combined method for calculation
    private void calculateMain() {
        String tokens[] = expression.split(",");
        for (int i = 0; i < tokens.length; i++) {
            if (!tokens[i].equals("") && !tokens[i].equals(" ") && !tokens[i].equals("\n") && !tokens[i].equals("  ")) {
                token.add(tokens[i]); // adding token to token array list from expression
            }
        }
        try {
            double res = Eval(infixTopostfix());
            result = Double.toString(res);
        } catch (Exception e) {
        }
    }

    // design of the frame with their action listner
    private void initialize() {
        frmCalculator = new JFrame();
        frmCalculator.setResizable(false);
        frmCalculator.setTitle("Assem's Scientific Calculator");
        frmCalculator.getContentPane().setBackground(new Color(155, 186, 99));
        frmCalculator.getContentPane().setFont(new Font("Calibri", Font.PLAIN, 15));
        frmCalculator.getContentPane().setForeground(SystemColor.windowBorder);
        frmCalculator.getContentPane().setLayout(null);

        JPanel textPanel = new JPanel();
        textPanel.setBorder(new BevelBorder(BevelBorder.LOWERED, null, null, null, null));
        textPanel.setBounds(34, 25, 316, 80);
        frmCalculator.getContentPane().add(textPanel);
        textPanel.setLayout(null);

        JLabel exprlabel = new JLabel("");
        exprlabel.setBackground(SystemColor.control);
        exprlabel.setFont(new Font("Yu Gothic UI Light", Font.PLAIN, 20));
        exprlabel.setHorizontalAlignment(SwingConstants.RIGHT);
        exprlabel.setForeground(UIManager.getColor("Button.disabledForeground"));
        exprlabel.setBounds(2, 2, 312, 27);
        textPanel.add(exprlabel);

        JTextField textField = new JTextField();
        exprlabel.setLabelFor(textField);
        textField.setHorizontalAlignment(SwingConstants.RIGHT);
        textField.setBackground(SystemColor.control);
        textField.setEditable(false);
        textField.setText("0");
        textField.setBorder(null);
        textField.setFont(new Font("Yu Gothic UI Light", textField.getFont().getStyle(), 32));
        textField.setBounds(2, 30, 312, 49);
        textPanel.add(textField);
        textField.setColumns(10);
        textField.addKeyListener(new KeyAdapter() {
            @Override
            public void keyPressed(KeyEvent e) {
                char keyChar = e.getKeyChar();
                if (Character.isDigit(keyChar) || keyChar == '.') {
                    if ("0".equals(textField.getText())) {
                        textField.setText("" + keyChar);
                    } else {
                        textField.setText(textField.getText() + keyChar);
                    }
                    if (num) {
                        expression += keyChar;
                    } else {
                        expression += "," + keyChar;
                    }
                    num = true;
                } else if (keyChar == '+' || keyChar == '-' || keyChar == '*' || keyChar == '/') {
                    String s = textField.getText();
                    if (!s.equals("0") && s.charAt(s.length() - 1) != keyChar) {
                        s += keyChar;
                        textField.setText(s);
                        expression += "," + keyChar;
                    }
                    num = false;
                    dot = false;
                } else if (keyChar == KeyEvent.VK_ENTER) {
                    calculateMain();
                    exprlabel.setText(expression + "=");
                    textField.setText(result);
                    expression = result;
                    dot = true;
                    num = true;
                    token.clear();
                } else if (keyChar == KeyEvent.VK_BACK_SPACE) {
                    String s = textField.getText();
                    if (s != "0" && s.length() > 1) {
                        String newString = s.substring(0, s.length() - 1);
                        textField.setText(newString);
                        if (expression.charAt(expression.length() - 1) == '.') {
                            dot = false;
                        }
                        if (expression.charAt(expression.length() - 1) == ',') {
                            expression = expression.substring(0, expression.length() - 2);
                        } else {
                            expression = expression.substring(0, expression.length() - 1);
                        }
                    } else {
                        textField.setText("0");
                        expression = "";
                    }
                }
            }
        });
        JPanel butttonPanel = new JPanel();
        butttonPanel.setBorder(new BevelBorder(BevelBorder.LOWERED, null, null, null, null));
        butttonPanel.setBackground(SystemColor.inactiveCaptionBorder);
        butttonPanel.setBounds(34, 120, 316, 322);
        frmCalculator.getContentPane().add(butttonPanel);
        butttonPanel.setLayout(new GridLayout(0, 5, 0, 0));

        // clear button
        JButton button1 = new JButton("C");
        button1.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                textField.setText("0");
                exprlabel.setText("");
                expression = "";
                token.clear();
                result = "";
                num = false;
                dot = false;
            }
        });
        button1.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button1);

        // delete button
        JButton button2 = new JButton("DEL");
        button2.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String s = textField.getText();
                if (s != "0" && s.length() > 1) {
                    String newString = s.substring(0, s.length() - 1);
                    textField.setText(newString);
                    if (expression.charAt(expression.length() - 1) == '.') {
                        dot = false;
                    }
                    if (expression.charAt(expression.length() - 1) == ',') {
                        expression = expression.substring(0, expression.length() - 2);
                    } else {
                        expression = expression.substring(0, expression.length() - 1);
                    }
                } else {
                    textField.setText("0");
                    expression = "";
                }
            }
        });
        button2.setFont(new Font("SansSerif", Font.PLAIN, 14));
        butttonPanel.add(button2);

        // button for constant pi
        JButton button3 = new JButton("<html><body><span>π</span></body></html>");
        button3.setFont(new Font("SansSerif", Font.PLAIN, 17));
        button3.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + Character.toString((char) 960));
                } else {
                    textField.setText(Character.toString((char) 960));
                }
                expression += ",pi";
                num = false;
                dot = false;
            }
        });
        butttonPanel.add(button3);

        // button for x^Y
        JButton button4 = new JButton("<html><body><span>X<sup>y</sup></span></body></html>");
        button4.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "^");
                    expression += ",^";
                } else {
                    textField.setText("0^");
                    expression += ",0,^";
                }
                num = false;
                dot = false;
            }
        });
        button4.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button4);

        // factorial button
        JButton buttton5 = new JButton("x!");
        buttton5.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "!");
                    expression += ",!";
                } else {
                    textField.setText("0!");
                    expression += ",0,!";
                }
                num = false;
                dot = false;
            }
        });
        buttton5.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(buttton5);

        // button for sin
        JButton button6 = new JButton("sin");
        button6.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "sin(");
                } else {
                    textField.setText("sin(");
                }
                expression += ",sin,(";
                num = false;
                dot = false;
            }
        });
        button6.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button6);

        JButton button7 = new JButton("(");
        button7.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "(");
                } else {
                    textField.setText("(");
                }
                expression += ",(";
                num = false;
                dot = false;
            }
        });
        button7.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button7);

        JButton button8 = new JButton(")");
        button8.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + ")");
                } else {
                    textField.setText(")");
                }
                expression += ",)";
                num = false;
                dot = false;
            }
        });
        button8.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button8);

        JButton button9 = new JButton("e");
        button9.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "e");
                } else {
                    textField.setText("e");
                }
                expression += ",e";
                num = false;
                dot = false;
            }
        });
        button9.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button9);

        // button for squre root
        JButton button10 = new JButton("<html><body><span>√</span></body></html>");
        button10.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + Character.toString((char) 8730));
                } else {
                    textField.setText(Character.toString((char) 8730));
                }
                expression += ",sqrt";
                num = false;
                dot = false;
            }
        });
        button10.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button10);

        JButton button11 = new JButton("cos");
        button11.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "cos(");
                } else {
                    textField.setText("cos(");
                }
                expression += ",cos,(";
                num = false;
                dot = false;
            }
        });
        button11.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button11);

        JButton button12 = new JButton("7");
        button12.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "7");
                } else {
                    textField.setText("7");
                }
                if (num) {
                    expression += "7";
                } else {
                    expression += ",7";
                }
                num = true;
            }
        });
        button12.setBackground(new Color(0, 220, 220));
        button12.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button12);

        JButton button13 = new JButton("8");
        button13.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "8");
                } else {
                    textField.setText("8");
                }
                if (num) {
                    expression += "8";
                } else {
                    expression += ",8";
                }
                num = true;
            }
        });
        button13.setBackground(new Color(0, 220, 220));
        button13.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button13);

        JButton button14 = new JButton("9");
        button14.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "9");
                } else {
                    textField.setText("9");
                }
                if (num) {
                    expression += "9";
                } else {
                    expression += ",9";
                }
                num = true;
            }
        });
        button14.setBackground(new Color(0, 220, 220));
        button14.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button14);

        // button for division operator
        JButton button15 = new JButton("<html><body><span>÷</span></body></html>");
        button15.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String s = textField.getText();
                if (s.equals("0")) {
                    expression += "0";
                }
                if (s.charAt(s.length() - 1) == '-' || s.charAt(s.length() - 1) == 'x'
                        || s.charAt(s.length() - 1) == '+') {
                    String newString = s.substring(0, s.length() - 1);
                    textField.setText(newString + Character.toString((char) 247));
                    expression = expression.substring(0, expression.length() - 1);
                    expression += "/";
                } else if (s.charAt(s.length() - 1) != (char) 247) {
                    textField.setText(s + Character.toString((char) 247));
                    expression += ",/";
                } else {
                    textField.setText(s);
                }
                num = false;
                dot = false;
            }
        });
        button15.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button15);

        JButton button16 = new JButton("tan");
        button16.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "tan(");
                } else {
                    textField.setText("tan(");
                }
                expression += ",tan,(";
                num = false;
                dot = false;
            }
        });
        button16.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button16);

        JButton button17 = new JButton("4");
        button17.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "4");
                } else {
                    textField.setText("4");
                }
                if (num) {
                    expression += "4";
                } else {
                    expression += ",4";
                }
                num = true;
            }
        });
        button17.setBackground(new Color(0, 220, 220));
        button17.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button17);

        JButton button18 = new JButton("5");
        button18.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "5");
                } else {
                    textField.setText("5");
                }
                if (num) {
                    expression += "5";
                } else {
                    expression += ",5";
                }
                num = true;
            }
        });
        button18.setBackground(new Color(0, 220, 220));
        button18.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button18);

        JButton button19 = new JButton("6");
        button19.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "6");
                } else {
                    textField.setText("6");
                }
                if (num) {
                    expression += "6";
                } else {
                    expression += ",6";
                }
                num = true;
            }
        });
        button19.setBackground(new Color(0, 220, 220));
        button19.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button19);

        JButton button20 = new JButton("x");
        button20.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {

                String s = textField.getText();
                if (s.equals("0")) {
                    expression += "0";
                }
                if (s.charAt(s.length() - 1) == '-' || s.charAt(s.length() - 1) == '+'
                        || s.charAt(s.length() - 1) == (char) (247)) {
                    String newString = s.substring(0, s.length() - 1);
                    newString += "x";
                    textField.setText(newString);
                    expression = expression.substring(0, expression.length() - 1);
                    expression += "x";
                } else if (s.charAt(s.length() - 1) != 'x') {
                    s += "x";
                    textField.setText(s);
                    expression += ",x";
                } else {
                    textField.setText(s);
                }
                num = false;
                dot = false;
            }
        });
        button20.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button20);

        JButton button21 = new JButton("ln");
        button21.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "ln(");
                } else {
                    textField.setText("ln(");
                }
                expression += ",ln,(";
                num = false;
                dot = false;
            }
        });
        button21.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button21);

        JButton button22 = new JButton("1");
        button22.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "1");
                } else {
                    textField.setText("1");
                }
                if (num) {
                    expression += "1";
                } else {
                    expression += ",1";
                }
                num = true;
            }
        });
        button22.setBackground(new Color(0, 220, 220));
        button22.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button22);

        JButton button23 = new JButton("2");
        button23.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "2");
                } else {
                    textField.setText("2");
                }
                if (num) {
                    expression += "2";
                } else {
                    expression += ",2";
                }
                num = true;
            }
        });
        button23.setBackground(new Color(0, 220, 220));
        button23.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button23);

        JButton button24 = new JButton("3");
        button24.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "3");
                } else {
                    textField.setText("3");
                }
                if (num) {
                    expression += "3";
                } else {
                    expression += ",3";
                }
                num = true;
            }
        });
        button24.setBackground(new Color(0, 220, 220));
        button24.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button24);

        JButton button25 = new JButton("-");
        button25.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String s = textField.getText();
                if (s.equals("0")) {
                    expression += "0";
                }
                if (s.charAt(s.length() - 1) == '+') {
                    String newString = s.substring(0, s.length() - 1);
                    newString += "-";
                    expression = expression.substring(0, expression.length() - 1);
                    expression += "-";
                    textField.setText(newString);
                } else if (s.charAt(s.length() - 1) != '-') {
                    s += "-";
                    textField.setText(s);
                    expression += ",-";
                } else {
                    textField.setText(s);
                }
                num = false;
                dot = false;
            }
        });
        button25.setFont(new Font("SansSerif", Font.BOLD, 23));
        butttonPanel.add(button25);

        JButton button26 = new JButton("<html><body><span>log<sub>10</sub></span></body></html>");
        button26.setFont(new Font("SansSerif", Font.PLAIN, 17));
        button26.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!"0".equals(textField.getText())) {
                    textField.setText(textField.getText() + "log(");
                } else {
                    textField.setText("log(");
                }
                expression += ",log,(";
                num = false;
                dot = false;
            }
        });
        butttonPanel.add(button26);

        JButton button27 = new JButton(".");
        button27.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String s = textField.getText();
                if (s.charAt(s.length() - 1) != '.') {
                    if (num && dot == false) {
                        expression += ".";
                        s += ".";
                    } else if (num == false && dot == false) {
                        expression += ",.";
                        s += ".";
                    }
                }
                num = true;
                dot = true;
                textField.setText(s);
            }
        });
        button27.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button27);

        JButton button28 = new JButton("0");
        button28.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if ("0".equals(textField.getText())) {
                    textField.setText("0");
                } else {
                    textField.setText(textField.getText() + "0");
                    if (num) {
                        expression += "0";
                    } else {
                        expression += ",0";
                    }
                }
                num = true;
            }
        });
        button28.setBackground(new Color(0, 220, 220));
        button28.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button28);

        // actual functioning on clicking = button
        JButton button29 = new JButton("=");
        button29.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                calculateMain();
                String s = "";
                token.remove(token.size() - 1);
                for (String i : token) {
                    if (i.equals("/")) {
                        s += Character.toString((char) 247);
                    } else if (i.equals("sqrt")) {
                        s += Character.toString((char) 8730);
                    } else if (i.equals("pi")) {
                        s += Character.toString((char) 960);
                    } else {
                        s += i;
                    }
                }
                exprlabel.setText(s + "=");
                textField.setText(result);

                expression = result;
                dot = true;
                num = true;
                token.clear();
            }
        });
        button29.setBackground(Color.ORANGE);
        button29.setFont(new Font("SansSerif", Font.PLAIN, 22));
        butttonPanel.add(button29);

        JButton button30 = new JButton("+");
        button30.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String s = textField.getText();
                if (s.equals("0")) {
                    expression += "0";
                }
                if (s.charAt(s.length() - 1) == '-' || s.charAt(s.length() - 1) == 'x'
                        || s.charAt(s.length() - 1) == (char) (247)) {
                    String newString = s.substring(0, s.length() - 1);
                    newString += "+";
                    textField.setText(newString);
                    expression = expression.substring(0, expression.length() - 1);
                    expression += "+";
                } else if (s.charAt(s.length() - 1) != '+') {
                    s += "+";
                    textField.setText(s);
                    expression += ",+";
                } else {
                    textField.setText(s);
                }
                num = false;
                dot = false;
            }
        });
        button30.setFont(new Font("SansSerif", Font.PLAIN, 17));
        butttonPanel.add(button30);
        frmCalculator.setBounds(200, 100, 400, 500);
        frmCalculator.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}