JApplet不显示绘画或绘制方法

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

Answer 2

Looks like you're passing the wrong reference to the createAndShowGui(..) method.

Try this on your Race class:

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) {
        Animation animie = new Animation();
        animie.createAndShowGUI(animie);
    }
}