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

/**
 *
 * @author aman
 */
public class Calculator extends JPanel {
    private JButton display;
    private JPanel panel;
    private double result;
    private String lastCommand;
    private boolean start;

    /**
     * Creates new form Calculator
     */
    public  Calculator() {
        setLayout(new BorderLayout());
        result=0;
        lastCommand= "=";
        start =true;

        display=new JButton("0");
        display.setEnabled(false);
        add(display,BorderLayout.NORTH);

        ActionListener insert= new InsertAction();
        ActionListener command= new CommandAction();

        panel= new JPanel();
        panel.setLayout(new GridLayout(4,4));

        addButton("7",insert);
        addButton("8",insert);
        addButton("9",insert);
        addButton("/",command);

        addButton("4",insert);
        addButton("5",insert);
        addButton("6",insert);
        addButton("*",command);

        addButton("1",insert);
        addButton("2",insert);
        addButton("3",insert);
        addButton("-",command);

        addButton("0",insert);
        addButton(".",insert);
        addButton("=",insert);
        addButton("+",insert);

        add(panel,BorderLayout.CENTER);



    }
    public void addButton(String label,ActionListener listener)
    {
        JButton button= new JButton(label);
        button.addActionListener(listener);
        panel.add(button);
    }

    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    private void initComponents() {

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 400, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 300, Short.MAX_VALUE)
        );

        pack();
    }// </editor-fold>

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(Calculator.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(Calculator.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(Calculator.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(Calculator.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {

            public void run() {
                new Calculator().setVisible(true);


            }
        });
    }

    // Variables declaration - do not modify
    // End of variables declaration

    private class InsertAction implements ActionListener {

        public InsertAction() {
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            String input=e.getActionCommand();
            if (start)
            {
                display.setText("");
                start=false;
            } else {
            }
            display.setText(display.getText()+input);
        }
    }

    private  class CommandAction implements ActionListener {

        public CommandAction() {
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            String command=e.getActionCommand();
            if (start)
            {
                if(command.equals("-"))
                {
                    display.setText(command);
                    start=false;
                }
                else
                    lastCommand=command;
            }
            else
            {
                calculate(Double.parseDouble(display.getText()));
                lastCommand=command;
                start=true;
            }


        }

        private void calculate(double x) {
            if(lastCommand.equals("+")) result +=x;
            else if(lastCommand.equals("-"))result -=x;
            else if(lastCommand.equals("*"))result *=x;
            else if(lastCommand.equals("/"))result /=x;
            else if(lastCommand.equals("="))result =x;
            display.setText(""+result);

        }
    }
}