Simpler GUI why doesnt it work

Code:

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import javax.swing.*;
import java.util.*;
public class Clock
{
        JFrame frame=new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setTitle("Clock");
        frame.setSize(550,220);
        JLabel display=new JLabel();
        display.setFont(new Font(Font.BOLD,38));
        frame.getContentPane().add(display);
        int last=-1;
        do
        {
                Date current=new Date();
                int sec=current.getSeconds();
                if(last!=sec)
                {
                        display.setText(current.toString());
                        last=sec;
                }
        }while(true);
}
}

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Why does it not work

should be something like this:

Code:

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import javax.swing.*;
import java.util.*;
import java.awt.*;
public class Clock extends JFrame
{
        public static void main(String[] args)
        {       
                JFrame frame=new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setTitle("Clock");
                frame.setPreferredSize(new Dimension(300,300));
                JLabel display=new JLabel();               
                frame.getContentPane().add(display);
                frame.pack();
                frame.setVisible(true);
                int last=-1;
                do
                {
                        Date current=new Date();
                        int sec=current.getSeconds();
                        if(last!=sec)
                        {
                                display.setText(current.toString());
                                last=sec;
                        }
                }while(true);
        }
}

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what does extends JFrame do
frame.pack(); this line too?

whoops well, you dont need to extend JFrame, so you can delete that. and frame.pack()

Quote:

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Causes this Window to be sized to fit the preferred size and layouts of its subcomponents. If the window and/or its owner are not yet displayable, both are made displayable before calculating the preferred size. The Window will be validated after the preferredSize is calculated.

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