Question

I have a animation class which simply draws two circles and a line (no main method), in another class i have a main method which is passed the animation class as a object and should show the two circles that I have drawn but it doesn’t show, it only shows the window none of the circles or the line that I have done, if i was to put the main method in my animation class it will work perfectly, this is a user error somehow but I’m not sure what or why.

The animation method in separate class.

import javax.swing.*;
import java.awt.geom.*;
import java.awt.*;
import java.awt.Graphics.*;
import javax.swing.JApplet;

public class Animation extends JApplet{

    public void init(){

}
public static void createAndShowGUI(JApplet j)
{
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    frame.pack();
    frame.setVisible(true);
    frame.setSize(500,500);

    frame.getContentPane().add("Center", j);
}

public void paint(Graphics g){
    Graphics2D g2 = (Graphics2D) g;
    int x=50;
    int y=10;
    g2.setPaint(Color.black);

    g2.draw(new Line2D.Double(x,y,50,400));

    drawT(g2);
    drawH(g2);  
        //create a method that translates
    }

public void drawH(Graphics2D g2)
{
    int y=25;
    g2.setColor(Color.blue);
    drawCircle(y,g2);
}

public void drawT(Graphics2D g2){
    int y=100;
    g2.setColor(Color.green);
    drawCircle(y,g2);
}/*
public void raceLoop(){
    long startingTime = System.currentTimeMillis();
    long cumTime=startingTime;
    while(mve.hposition<70){
        long timePassed = System.currentTimeMillis()-cumTime;   
        cumTime += timePassed;
        //mve.update(timePassed);   
    }
}*/

public void drawCircle(int y, Graphics2D g2)
{
g2.fillOval(50,y,50,50);
}
}

The Main Method

import javax.swing.*;
import java.awt.geom.*;
import java.awt.*;
import java.awt.Graphics.*;
import javax.swing.JApplet;

public class Race {

public static void main(String[] args) {
    JApplet applet = new JApplet();
    Animation animie = new Animation();
    animie.createAndShowGUI(applet);

}
}

Answer 1

1. You don’t need to (or want) extend from JApplet if all you’re going to is use a JFrame. You’re better of (in any case), extending from JPanel (as this can then be added to a JApplet or JFrame)
2. You’ve not added anything to the JFrame, so, in fact, you program is doing exactly what you told it to.
3. You should very rarely need to override the paint method of a top level container (like JApplet or JFrame), instead, use JPanel and override it’s paintComponent method.
4. You should always call super.paintXxx, the paint methods chain together to paint the various aspects of the application and it will end in tears if you break this chain.

You might like to have a read through

• Creating a GUI With JFC/Swing
• Performing Custom Painting
• Painting in AWT and Swing

For some more background