Simple Accumulator

Sandbox.java

import javax.swing.*;
import javax.swing.border.BevelBorder;
import java.awt.*;
import java.awt.event.*;
import java.util.TimerTask;

public class Sandbox extends JFrame implements ActionListener {

    private JLabel label;
    private JTextField txtField;
    private JButton increment;
    private JButton clear;

    private int count = 0;

    private Sandbox() throws HeadlessException {

        Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();

        this.setTitle("Counter");
        this.setSize(300, 95);
        this.setLocation(dim.width / 2 - this.getSize().width / 2, dim.height / 2 - this.getSize().height / 2);
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.setVisible(true);

        Container contentPane = this.getContentPane();
        contentPane.setLayout(new BorderLayout());
        contentPane.setBackground(new Color(88, 88, 89));

        JPanel panel_1 = new JPanel(new GridLayout(1, 2));

        label = new JLabel("Counter");
        label.setHorizontalAlignment(JLabel.CENTER);
        label.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {

                label.setText("BOI, don't click me!");

                (new java.util.Timer()).schedule(new TimerTask() {
                    @Override
                    public void run() {
                        label.setText("Counter");
                    }
                }, 3 * 1000);
            }
        });

        txtField = new JTextField();
        txtField.setEditable(false);
        txtField.setBorder(new BevelBorder(BevelBorder.LOWERED));
        txtField.setHorizontalAlignment(JTextField.CENTER);
        txtField.setText(Integer.toString(count));
        txtField.setPreferredSize(new Dimension(20, 30));

        panel_1.add(label);
        panel_1.add(txtField);

        JPanel panel_2 = new JPanel(new GridLayout(1, 2));

        increment = new JButton("Increment");
        increment.addActionListener(this);
        increment.setMnemonic(KeyEvent.VK_I);

        clear = new JButton("Clear");
        clear.addActionListener(this);
        clear.setMnemonic(KeyEvent.VK_C);

        panel_2.add(increment);
        panel_2.add(clear);

        contentPane.add(panel_1, BorderLayout.NORTH);
        contentPane.add(panel_2, BorderLayout.SOUTH);

        this.update();

    }

    @Override
    public void actionPerformed(ActionEvent e) {

        if (e.getSource() == increment)
            count += 1;
        else
            count = 0;

        txtField.setText(Integer.toString(count));
        this.update();
    }

    private void update() {
        this.repaint();
        this.revalidate();
    }

    public static void main(String[] args) {
        Sandbox a = new Sandbox();
    }
}