MyException.java

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

public class MyException extends JFrame implements ActionListener {
	JButton calculate;
	JTextField input;
	JLabel output;
	
	public MyException() {
		this.setSize(250, 350);
		this.setLayout(null);
		
		JLabel val = new JLabel("value >= 0");
		val.setBounds(20, 50, 100, 50);
		this.getContentPane().add(val);
		
		input = new JTextField("0");
		input.setBounds(130, 50, 100, 50);
		this.getContentPane().add(input);
		
		val = new JLabel("Square root");
		val.setBounds(20, 150, 100, 50);
		this.getContentPane().add(val);
		
		output = new JLabel("");
		output.setBounds(130, 150, 100, 50);
		this.getContentPane().add(output);
		
		calculate = new JButton("Calculate");
		calculate.setBounds(80, 250, 100, 50);
		this.getContentPane().add(calculate);
		calculate.addActionListener(this);
	}
	
	public static void main(String[] args) {
		new MyException().setVisible(true);
	}
	
	public void actionPerformed(ActionEvent e) {
		if (e.getSource() == calculate) {
			try {
				double value = Double.parseDouble(input.getText().trim());
				output.setText("" + Math.sqrt(value));
			} catch (NumberFormatException _) {
				JOptionPane.showMessageDialog(this, "NOT A NUMBER!", "Error!", JOptionPane.ERROR_MESSAGE);
			}
		}
	}
}