Simple Calculator

import javax.swing.*;
import java.awt.GridLayout;
import java.awt.BorderLayout;

// Declaring all calculator’s components.
public class Calculator
{
    JPanel windowContent;
    JTextField displayField;
    JButton button0;
    JButton button1;
    JButton button2;
    JButton button3;
    JButton button4;
    JButton button5;
    JButton button6;
    JButton button7;
    JButton button8;
    JButton button9;
    JButton buttonPoint;
    JButton buttonEqual;
    JPanel p1;

    Calculator()
    {
        windowContent = new JPanel();
        // Setting the layout manager for the panel.
        BorderLayout b1 = new BorderLayout();
        windowContent.setLayout(b1);
        // Creating the display field.
        displayField = new JTextField(30);
        windowContent.add("North", displayField);
        // Creating the buttons
        button0 = new JButton("0");
        button1 = new JButton("1");
        button2 = new JButton("2");
        button3 = new JButton("3");
        button4 = new JButton("4");
        button5 = new JButton("5");
        button6 = new JButton("6");
        button7 = new JButton("7");
        button8 = new JButton("8");
        button9 = new JButton("9");
        buttonPoint = new JButton(".");
        buttonEqual = new JButton("=");
        // Create the panel with the GridLayout with 12 buttons
        // 10 numeric ones, period, and the equal sign
        p1 = new JPanel();
        GridLayout g1 = new GridLayout(4, 3);
        p1.setLayout(g1);
        p1.add(button1);
        p1.add(button2);
        p1.add(button3);
        p1.add(button4);
        p1.add(button5);
        p1.add(button6);
        p1.add(button7);
        p1.add(button8);
        p1.add(button9);
        p1.add(button0);
        p1.add(buttonPoint);
        p1.add(buttonEqual);
        // Adding the panel p1 to the center of the window
        windowContent.add("Center", p1);
        // Creating the frame and set its content pane
        JFrame frame = new JFrame("Calculator");
        frame.setContentPane(windowContent);
        // Setting the size of the window big enough to accomodate
        frame.pack();
        // Display the window
        frame.setVisible(true);
    }

    public static void main(String[] args)
    {
        Calculator calc = new Calculator();
    }
}