How do I use a JFrame class as main class?

Question

I'm trying to build a calculator.

I've developed the interface using the Swing plug-in (containers and controls), but when I try to run my program it says the package needs a main class.

Already tried to create a main class and call the Calc() JFrame class, but it didn't work.

Take a look at the code:

public class Calc extends javax.swing.JPanel {
    public Calc() {
        initComponents();
    }
}

Answer 1

You need a main() method to execute your class.

Take a look at the FrameDemo example code found in the Swing tutorial on How to Make Frames for a basic example to get you started.

/* FrameDemo.java requires no other files. */
public class FrameDemo {

/**
 * Create the GUI and show it.  For thread safety,
 * this method should be invoked from the
 * event-dispatching thread.
 */
private static void createAndShowGUI() {
    //Create and set up the window.
    JFrame frame = new JFrame("FrameDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JLabel emptyLabel = new JLabel("");
    emptyLabel.setPreferredSize(new Dimension(175, 100));
    frame.getContentPane().add(emptyLabel, BorderLayout.CENTER);

    //Display the window.
    frame.pack();
    frame.setVisible(true);
}

public static void main(String[] args) {
    //Schedule a job for the event-dispatching thread:
    //creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            createAndShowGUI();
        }
    });
  }
}