Show .png image in a JFrame?

Question

I am a little stuck. Why wont this work? I just get a error saying:

java.lang.NoSuchMethodError: main

Exception in thread "main"

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Answer 1

This was the finished code:

import java.awt.*;  
import javax.swing.*;  

@SuppressWarnings("serial") 
public class ShowPNG extends JFrame {   

  public ShowPNG(String argx) { 
    if ( argx == null ) {
      argx = "a.png";
 }   
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
 this.setSize(500,640);
    JPanel panel = new JPanel();  
    //panel.setSize(500,640);
    panel.setBackground(Color.CYAN);  
    ImageIcon icon = new ImageIcon(argx);  
    JLabel label = new JLabel();  
    label.setIcon(icon);  
    panel.add(label); 
    this.getContentPane().add(panel);    
  } 

  public static void main(String[] args) { 
      new ShowPNG(args.length == 0 ? null : args[0]).setVisible(true);
  } 

}