Simple Calculator

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

class Calculator extends JFrame implements ActionListener{
    JButton b0,b1,b2,b3,b4,b5,b6,b7,b8,b9,b_add,b_sub,b_multi,b_div,b_clear,b_del,b_dot,b_equals;
    JTextField text;
    static double variable = 0, result = 0;
    static String sResult = "";
    static int operationNumber = -1;
    Calculator(){
        setLayout(null);
        setResizable(false);
        setSize(350,550);

        text = new JTextField(10);
        text.setEditable(false);

        b0 = new JButton("0");
        b1 = new JButton("1");
        b2 = new JButton("2");
        b3 = new JButton("3");
        b4 = new JButton("4");
        b5 = new JButton("5");
        b6 = new JButton("6");
        b7 = new JButton("7");
        b8 = new JButton("8");
        b9 = new JButton("9");
        b_equals = new JButton("=");
        b_dot = new JButton(".");
        b_add = new JButton("+");
        b_sub = new JButton("-");
        b_multi = new JButton("*");
        b_div = new JButton("/");
        b_del = new JButton("del");
        b_clear = new JButton("clear");

        text.setBounds(20,20,290,70);

        b7.setBounds(30,110,60,60);
        b8.setBounds(100,110,60,60);
        b9.setBounds(170,110,60,60);
        b_div.setBounds(240,110,60,60);

        b4.setBounds(30,190,60,60);
        b5.setBounds(100,190,60,60);
        b6.setBounds(170,190,60,60);
        b_multi.setBounds(240,190,60,60);

        b1.setBounds(30,270,60,60);
        b2.setBounds(100,270,60,60);
        b3.setBounds(170,270,60,60);
        b_sub.setBounds(240,270,60,60);

        b_dot.setBounds(30,350,60,60);
        b0.setBounds(100,350,60,60);
        b_equals.setBounds(170,350,60,60);
        b_add.setBounds(240,350,60,60);

        b_clear.setBounds(30,430,130,60);
        b_del.setBounds(170,430,130,60);

        add(text);
        add(b0);
        add(b1);
        add(b2);
        add(b3);
        add(b4);
        add(b5);
        add(b6);
        add(b7);
        add(b8);
        add(b9);
        add(b_dot);
        add(b_add);
        add(b_sub);
        add(b_multi);
        add(b_div);
        add(b_del);
        add(b_clear);
        add(b_equals);

        setVisible(true);

        b0.addActionListener(this);
        b1.addActionListener(this);
        b2.addActionListener(this);
        b3.addActionListener(this);
        b4.addActionListener(this);
        b5.addActionListener(this);
        b6.addActionListener(this);
        b7.addActionListener(this);
        b8.addActionListener(this);
        b9.addActionListener(this);
        b_equals.addActionListener(this);
        b_dot.addActionListener(this);
        b_add.addActionListener(this);
        b_sub.addActionListener(this);
        b_multi.addActionListener(this);
        b_div.addActionListener(this);
        b_del.addActionListener(this);
        b_clear.addActionListener(this);

    }
    public void actionPerformed(ActionEvent e){
        try {
            if (e.getSource() == b0)
                text.setText(text.getText().concat("0"));
            if (e.getSource() == b1)
                text.setText(text.getText().concat("1"));
            if (e.getSource() == b2)
                text.setText(text.getText().concat("2"));
            if (e.getSource() == b3)
                text.setText(text.getText().concat("3"));
            if (e.getSource() == b4)
                text.setText(text.getText().concat("4"));
            if (e.getSource() == b5)
                text.setText(text.getText().concat("5"));
            if (e.getSource() == b6)
                text.setText(text.getText().concat("6"));
            if (e.getSource() == b7)
                text.setText(text.getText().concat("7"));
            if (e.getSource() == b8)
                text.setText(text.getText().concat("8"));
            if (e.getSource() == b9)
                text.setText(text.getText().concat("9"));
            if (e.getSource() == b_dot)
                text.setText(text.getText().concat("."));
            else if (e.getSource() == b_add) {
                operationNumber = 1;
                variable = Double.parseDouble(text.getText());
                clearTextBox();
            } else if (e.getSource() == b_sub) {
                operationNumber = 2;
                variable = Double.parseDouble(text.getText());
                clearTextBox();
            } else if (e.getSource() == b_multi) {
                operationNumber = 3;
                variable = Double.parseDouble(text.getText());
                clearTextBox();
            } else if (e.getSource() == b_div) {
                operationNumber = 4;
                variable = Double.parseDouble(text.getText());
                clearTextBox();
            } else if (e.getSource() == b_del) {

                if (text.getText().length() != 0) {
                    String temp = text.getText();
                    clearTextBox();

                    for (int i = 0; i < temp.length() - 1; i++)
                        text.setText(text.getText() + temp.charAt(i));
                }

            } else if (e.getSource() == b_clear) {
                clearTextBox();
            } else if (e.getSource() == b_equals) {

                if (operationNumber == 1) {
                    result = variable + Double.parseDouble(text.getText());
                }
                if (operationNumber == 2) {
                    result = variable - Double.parseDouble(text.getText());
                }
                if (operationNumber == 3) {
                    result = variable * Double.parseDouble(text.getText());
                }
                if (operationNumber == 4) {
                    result = variable / Double.parseDouble(text.getText());
                }
                text.setText("" + result);
            }
        }
        catch (Exception err){}


    }
    void clearTextBox() {
        text.setText("");
    }
}

public class Main{
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable(){
            public void run(){
                new Calculator();
            }
        });
    }

}