Calculator.java

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

public class Calculator extends JFrame
{
   private JTextField answerfield;
   private JButton one, two, three, four, five, six, seven, eight, nine, zero, add, sub, mul, div, equ;
   private String input1, input2, output;
   private double answer = 0.0;
   private boolean equalsClicked = false, opChosen = false;

	public static void createAndShowGUI()
	{
		// FRAME
		JFrame frame = new JFrame("Calculator");

		// NORTH SCREEN
		JPanel screen = new JPanel();
		screen.setPreferredSize(new Dimension(250, 60));
		frame.add(screen, BorderLayout.NORTH);

		// NORTH TEXT INPUT
		JTextField answerfield = new JTextField();
		answerfield.setPreferredSize(new Dimension(240, 50));
		screen.add(answerfield);

      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
		frame.pack();
      frame.setVisible(true);

		// SOUTH SCREEN
		JPanel buttons = new JPanel();
		buttons.setPreferredSize(new Dimension(250, 300));
		frame.add(buttons, BorderLayout.SOUTH);

      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
		frame.pack();
      frame.setVisible(true);

      JPanel button = new JPanel();
      button.setPreferredSize(new Dimension(230, 250));
      buttons.add(button);

      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
		frame.pack();
      frame.setVisible(true);

		// SOUTH BUTTONS
		button.setLayout(new GridLayout(4, 4, 8, 12));
		JButton seven = new JButton("7");
		button.add(seven);

		JButton eight = new JButton("8");
		button.add(eight);

		JButton nine = new JButton("9");
		button.add(nine);

		JButton div = new JButton("/");
		button.add(div);

		JButton four = new JButton("4");
		button.add(four);

		JButton five = new JButton("5");
		button.add(five);

		JButton six = new JButton("6");
		button.add(six);

		JButton mul = new JButton("*");
		button.add(mul);

		JButton one = new JButton("1");
		button.add(one);

		JButton two = new JButton("2");
		button.add(two);

		JButton three = new JButton("3");
		button.add(three);

		JButton sub = new JButton("-");
		button.add(sub);

		JButton zero = new JButton("0");
		button.add(zero);

		JButton dec = new JButton(".");
		button.add(dec);

		JButton equ = new JButton("=");
		button.add(equ);

		JButton addbutton = new JButton("+");
		button.add(addbutton);

      Numbers n = new Numbers();
      Calculations c = new Calculations();

   // ADD ACTION LISTENERS
      one.addActionListener(n);
      two.addActionListener(n);
      three.addActionListener(n);
      four.addActionListener(n);
      five.addActionListener(n);
      six.addActionListener(n);
      seven.addActionListener(n);
      eight.addActionListener(n);
      nine.addActionListener(n);
      zero.addActionListener(n);
	}

   // NUMBER'S ACTION LISTENERS
   private class Numbers implements ActionListener
   {
      public void actionPerformed(ActionEvent event)
      {
         JButton src = (JButton) event.getSource();

         if(src.equals(one))
         {
            if(opChosen = false)
            {
               if(input1 == null)
               {
                  input1 = "1";
               }
               else
               {
                  input1 = input1 + "1";
               }
            }
            else
            {
               if(input2 == null)
               {
                  input2 = "1";
               }
               else
               {
                  input2 = input2 + "1";
               }
            }
         }
         if(src.equals(two))
         {
            if(opChosen = false)
            {
               if(input1 == null)
               {
                  input1 = "2";
               }
               else
               {
                  input1 = input1 + "2";
               }
            }
            else
            {
               if(input2 == null)
               {
                  input2 = "2";
               }
               else
               {
                  input2 = input2 + "2";
               }
            }
         }
         if(src.equals(three))
         {
            if(opChosen = false)
            {
               if(input1 == null)
               {
                  input1 = "3";
               }
               else
               {
                  input1 = input1 + "3";
               }
            }
            else
            {
               if(input2 == null)
               {
                  input2 = "3";
               }
               else
               {
                  input2 = input2 + "3";
               }
            }
         }
         if(src.equals(four))
         {
            if(opChosen = false)
            {
               if(input1 == null)
               {
                  input1 = "4";
               }
               else
               {
                  input1 = input1 + "4";
               }
            }
            else
            {
               if(input2 == null)
               {
                  input2 = "4";
               }
               else
               {
                  input2 = input2 + "4";
               }
            }
         }
         if(src.equals(five))
         {
            if(opChosen = false)
            {
               if(input1 == null)
               {
                  input1 = "5";
               }
               else
               {
                  input1 = input1 + "5";
               }
            }
            else
            {
               if(input2 == null)
               {
                  input2 = "5";
               }
               else
               {
                  input2 = input2 + "5";
               }
            }
         }
         if(src.equals(six))
         {
            if(opChosen = false)
            {
               if(input1 == null)
               {
                  input1 = "6";
               }
               else
               {
                  input1 = input1 + "6";
               }
            }
            else
            {
               if(input2 == null)
               {
                  input2 = "6";
               }
               else
               {
                  input2 = input2 + "6";
               }
            }
         }
         if(src.equals(seven))
         {
            if(opChosen = false)
            {
               if(input1 == null)
               {
                  input1 = "7";
               }
               else
               {
                  input1 = input1 + "7";
               }
            }
            else
            {
               if(input2 == null)
               {
                  input2 = "7";
               }
               else
               {
                  input2 = input2 + "7";
               }
            }
         }
         if(src.equals(eight))
         {
            if(opChosen = false)
            {
               if(input1 == null)
               {
                  input1 = "8";
               }
               else
               {
                  input1 = input1 + "8";
               }
            }
            else
            {
               if(input2 == null)
               {
                  input2 = "8";
               }
               else
               {
                  input2 = input2 + "8";
               }
            }
         }
         if(src.equals(nine))
         {
            if(opChosen = false)
            {
               if(input1 == null)
               {
                  input1 = "9";
               }
               else
               {
                  input1 = input1 + "9";
               }
            }
            else
            {
               if(input2 == null)
               {
                  input2 = "9";
               }
               else
               {
                  input2 = input2 + "9";
               }
            }
         }
         if(src.equals(zero))
         {
            if(opChosen = false)
            {
               if(input1 == null)
               {
                  input1 = "0";
               }
               else
               {
                  input1 = input1 + "0";
               }
            }
            else
            {
               if(input2 == null)
               {
                  input2 = "0";
               }
               else
               {
                  input2 = input2 + "0";
               }
            }
         }
         if(equalsClicked==false)
         {
            if(opChosen==false)
            {
               answerfield.setText(input1);
            }
            else
            {
               answerfield.setText(input2);
            }
         }
      }
   }

   // ADD CALCULATIONS'S ACTION LISTENERS
   private class Calculations implements ActionListener
   {
      public void actionPerformed(ActionEvent event)
      {
         JButton src = (JButton) event.getSource();
      }
   }

   // MAIN FUNCTION
	public static void main(String[] args)
	{
		SwingUtilities.invokeLater(new Runnable()
		{
			public void run()
			{
				createAndShowGUI();
			}
		});
	}
}