import java.awt.*;					// for layout managers
import java.awt.event.*;			// for ActionListener/ActionEvent
import javax.swing.*;				// JPanel, JFrame

public class Ch16_4					// create a simple GUI calculator with JButtons, JLabels and JTextFields
{
	public static void main(String[] args)
	{
		JFrame f=new JFrame("calculator");
		f.setSize(550,125);
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		CalculatorPanel cp=new CalculatorPanel();
		f.add(cp);
		f.setVisible(true);
	}
	
	public static class CalculatorPanel extends JPanel implements ActionListener		// for JButtons
	{
		private JTextField f1, f2, f3;				// f1 and f2 will be for input, f3 for output (could be a JLabel)
		private JButton add, sub, mul, div;			// our JButtons to do the 4 arithmetic operations for the calculator

		public CalculatorPanel()
		{
			add=new JButton("Add");					// create the JButtons
			sub=new JButton("Subtract");
			mul=new JButton("Multiply");
			div=new JButton("Divide");
			add.addActionListener(this);			// add this as their ActionListeners
			sub.addActionListener(this);
			mul.addActionListener(this);
			div.addActionListener(this);
			JLabel lab1=new JLabel("Number 1");		// create the 3 JLabels for each of the JTextFields
			JLabel lab2=new JLabel("Number 2");
			JLabel lab3=new JLabel("Result");
			f1=new JTextField("",10);				// create the 3 JTextFields, all initially blank
			f2=new JTextField("",10);
			f3=new JTextField("",10);
			f3.setEditable(false);					// f3 will be used for output only so is not editable (could be a JLabel)
			JPanel p1=new JPanel();					// create a JPanel for the JLabels and JTextFields
			p1.add(lab1);
			p1.add(f1);
			p1.add(lab2);
			p1.add(f2);
			p1.add(lab3);
			p1.add(f3);
			JPanel p2=new JPanel();					// create a JPanel for the 4 JButtons
			p2.add(add);
			p2.add(sub);
			p2.add(mul);
			p2.add(div);
			JPanel p3=new JPanel(new GridLayout(2,1));	// add the two JPanels, one per row
			p3.add(p1);
			p3.add(p2);
			add(p3);								// add the last JPanel to this
		}
		
		public void actionPerformed(ActionEvent e)		// upon a JButton press
		{
			double num1, num2, result;
			num1=Double.parseDouble(f1.getText());		// get the two input numbers as doubles
			num2=Double.parseDouble(f2.getText());
			if(e.getSource()==add)						// perform the arithmetic operation based on the JButton pressed, storing result in result
				result=num1+num2;
			else if(e.getSource()==sub)
				result=num1-num2;
			else if(e.getSource()==mul)
				result=num1*num2;
			else result=num1/num2;
			f3.setText(""+result);						// display the result
		}			
	}
}