I tried some swing today for a GUI in java. When I want to launch the application, this error appears. Here is my source code:
package de.hoffmann;
import java.awt.Color;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class MainApplication extends javax.swing.JFrame {
private static final long serialVersionUID = 1L;
public MainApplication() {
JFrame mainFrame = new JFrame("Buchstaben-Häufigkeit");
mainFrame.setSize(600,400);
JPanel panel = new JPanel();
panel.setBackground(Color.red);
mainFrame.add(panel);
pack();
}
public static void main(String[] args) {
new MainApplication().setVisible(true);
}
}
Where's the problem