[JAVA] Problema con calcolatrice

[protest00]

Salve,
ho voluto fare un semplice calcolatore che somma due numeri.
Eclipse compila ma quando inserisco i due numeri non mi restituisce alcuna somma e non capisco perchè.

Posto il codice completo qui in basso.

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;



public class Calcolatrice extends JFrame {
	
	public JButton addButton;
	public JTextField firstNumber;
	public JTextField secondNumber;
	public JTextField answer;
	public JLabel answerLabel;
		

	public Calcolatrice(){
		this.setTitle("Calcolatrice");
		this.setSize(new Dimension(260,165));
		this.setLocation(MouseInfo.getPointerInfo().getLocation());
		this.setLayout(new FlowLayout());
		this.setResizable(false);
		this.addComponentListener(new ComponentListener(){

			@Override
			public void componentHidden(ComponentEvent e) {}

			public void componentMoved(ComponentEvent e) {}

			public void componentResized(ComponentEvent e){}
			
			public void componentShown(ComponentEvent e) {
				Calcolatrice_Load();
			}
			
		});
		
		
		
		this.addButton = new JButton();
		this.addButton.setText("Add");
		this.addButton.addActionListener(new ActionListener(){
			
			public void actionPerformed(ActionEvent e){
				addButton_ActionPerformed();
			}
		});
		
		this.firstNumber = new JTextField();
		this.firstNumber.setText("                                                           ");
		
		this.secondNumber = new JTextField();
		this.secondNumber.setText("                                                              ");
		
		this.answer = new JTextField();
		this.answer.setText("                                                   ");
		this.answer.setEditable(false);
		
		this.answerLabel = new JLabel();
		this.answerLabel.setText("Risultato:                                                      ");
		
		add(addButton);
		add(firstNumber);
		add(secondNumber);
		add(answerLabel);
		add(answer);
			
	}
	
	private void Calcolatrice_Load(){
		firstNumber.setText("                                 ");
		secondNumber.setText("                                ");
		answer.setText("                      ");
		
	}
	
	private void addButton_ActionPerformed(){
		
		try{
		     int num1 , num2;
		     num1 = Integer.parseInt(firstNumber.getText());
		     num2 = Integer.parseInt(secondNumber.getText());
		     int answer2 = num1+num2;
		     answer.setText(String.valueOf(answer2));
		}catch(Exception ex){
		
		}
		
	}
}

public class main {
	
	public static void main(String[] args){
		
		Calcolatrice newform = new Calcolatrice();
		newform.setVisible(true);
		
	}

}