Extending JFrame to a subclass and testing it

Question

I am following an example in my textbook that goes like this:
package project2;
import javax.swing.JFrame;
class PracticeWithJFrame2 extends JFrame
     private static final int FRAME_WIDTH=300;
     private static final int FRAME_HEIGHT=200;
     private static final int FRAME_X_ORIGIN=150;
     private static final int FRAME_Y_ORIGIN=250;
     public PracticeWithJFrame2()
          // set the frame default properties
          setTitle("My First Subclass");
          setSize(FRAME_WIDTH, FRAME_HEIGHT);
          setLocation(FRAME_X_ORIGIN,FRAME_Y_ORIGIN);
          // register 'Exit upon closing' as a default close operation
          setDefaultCloseOperation(EXIT_ON_CLOSE);
}in the testing class:
package project2;
class TestPracticeJFrameClass {
      * @param args
     public static void main(String[] args) {
          PracticeWithJFrame2 myFrame;
          myFrame = new PracticeWithJFrame2();
          myFrame.setVisible(true);
}2 errors are ocurring:
1) Multiple markers at this line
     - The serializable class PracticeWithJFrame2 does not declare a static final
      serialVersionUID field of type long
     - The type PracticeWithJFrame2 is already defined2) the test case brings up a JFrame window, but it is basically an empty window, it didn't take on the values the constructor set for it.
Thanks for some debugging help

Answer 1

I'll get back to you in a moment, in the meantime I've got a work around solution. I did the testing/application in a single class, by calling the constructor in the main method:
package project2;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class Ch14JButtonEvents extends JFrame
     private static final int FRAME_WIDTH=300;
     private static final int FRAME_HEIGHT=200;
     private static final int FRAME_X_ORIGIN=150;
     private static final int FRAME_Y_ORIGIN=250;
     private static final int BUTTON_WIDTH=80;
     private static final int BUTTON_HEIGHT=30;
     private JButton cancelButton;
     private JButton okButton;
     public static void main(String[] args)
          PracticeWithJButton frame = new PracticeWithJButton();
          frame.setVisible(true);
     public Ch14JButtonEvents()
          Container contentPane = getContentPane();
          // set the frame default properties
          setTitle("Program PracticeWithJButton");
          setResizable(false);
          setSize(FRAME_WIDTH, FRAME_HEIGHT);
          setLocation(FRAME_X_ORIGIN,FRAME_Y_ORIGIN);
          // set the layout manager
          contentPane.setLayout(new FlowLayout());
          // create and place two buttons on the frame's content pane
          okButton = new JButton("OK");
          okButton.setSize(BUTTON_WIDTH, BUTTON_HEIGHT);
          contentPane.add(okButton);
          cancelButton = new JButton("CANCEL");
          cancelButton.setSize(BUTTON_WIDTH, BUTTON_HEIGHT);
          contentPane.add(cancelButton);
          // register 'Exit upon closing' as a default close operation
          setDefaultCloseOperation(EXIT_ON_CLOSE);
}