Thread: I've never seen these erros before

I am in the process of writing a code that involves buttons and a displaypanel and a lot of different things, so ive decided to Test as I go with every aspect of the code. I tried setting up just the background display with a line and two rectangles and i got errors. here is my code:

import java.awt.*;
import javax.swing.*;
 
public class SaucerPanel extends JPanel{
static final long serialVersionUID = 1;
public SaucerPanel(){
setPreferredSize(new Dimension(500,400));
setBackground(Color.red);
 }
public void paintComponent(Graphics g){
super.paintComponent(g);
g.drawLine(0,380,500,380);
g.drawRect(111,180,200,100);
g.drawString("hovering...", 10, 15);
}
}

and it compiled just fine but when i hit Run on Dr. Java I got this under the Interactions Panel
java.lang.NoSuchMethodError: main
at sun.reflect.NativeConstructorAccessorImpl.newInsta nce0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInsta nce(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newI nstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at edu.rice.cs.dynamicjava.symbol.JavaClass$JavaConst ructor.evaluate(JavaClass.java:298)
at edu.rice.cs.dynamicjava.interpreter.ExpressionEval uator.handleConstructor(ExpressionEvaluator.java:1 28)
at edu.rice.cs.dynamicjava.interpreter.ExpressionEval uator.visit(ExpressionEvaluator.java:98)
at koala.dynamicjava.tree.SimpleAllocation.acceptVisi tor(SimpleAllocation.java:137)
at edu.rice.cs.dynamicjava.interpreter.ExpressionEval uator.value(ExpressionEvaluator.java:38)

can anyone explain/help me with this

Every application in java requires a program entry point, which is the main method (see Lesson: A Closer Look at the "Hello World!" Application (The Java™ Tutorials > Getting Started)). The code you posted needs this entry point. In your case you need a bit more because the JPanel itself needs to be added to a top level container (see Using Top-Level Containers and How to Make Frames) for it to be visible.