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Thread: I've never seen these erros before

  1. #1
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    Default 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


  2. #2
    Administrator copeg's Avatar
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    Default Re: I've never seen these erros before

    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.