import javax.swing.*;

/**
 * Class to test simple use of a button.
 * It should show a count of the button clicks in the label.
 */
public class ButtonTest extends JPanel {
    JLabel countLabel;
    JButton button;
    public ButtonTest() {
        countLabel = new JLabel("0");
        button = new JButton("Click me");
        add(button);
        add(countLabel);
    }
    
    // Set up main window and add our components.
    public static void buildGUI() {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setContentPane(new ButtonTest());
        frame.pack();
        frame.setVisible(true);
    }
    
    public static void main(String[] args) {
        // A thread is a single sequence of logic within a program.  A single
        // program can have multiple threads executing concurrently.  The Swing
        // library is not thread safe, meaning that we can't work with it in
        // multiple concurrent threads.  Almost all Swing code must execute in a
        // special thread called the event dispatch thread.  The invokeLater
        // method allows us to run code on that thread, to make sure that no
        // errors can occur due to threading issues (even though for our simple
        // program such an error is very unlikely to happen).  The input makes
        // use of the Runnable interface, which we're creating an anonymous
        // class to implement.
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                buildGUI();
            }
        });
    }
}