Java- Not able to animate square, comes out as rotating square

Question

I am new to java and need some help! My professor wants me to create 4 methods, which ultimate goal is to output a animated rotating square like I did in this earlier code that I made:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class GTest2 {
public static void main(String[] args) {
    GraphicsPanel gp = new GraphicsPanel();
    gp.delay(1000);
    int x = gp.getWidth() / 2;
    int y = gp.getHeight() / 2;
    gp.setLocation(x, y);
    for (int n=1; n <= 150; n++)  {
        gp.clear();
        for (int angle=0; angle < 360; angle += 10) {
            for (int i=0; i < 4; i++)  {             
                gp.draw(100);
                gp.turn(90);
            }
            gp.turn(10);
        }
        gp.render();        
        gp.delay(30);       
        gp.turn(2);         
    }
}
}

My professor supplied us class GraphicsPanel so we could do these programs of creating shapes and animations: http://pastebin.com/Ha1pdLrc

This is what I have so far, but I seem to only have been able to create a rotating square:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class G7 {
    public static void main(String[] args) {
        GraphicsPanel gp = new GraphicsPanel();
        gp.delay(1000);         
        animateCircleOfPolygons(gp);
    }

public static void animateCircleOfPolygons(GraphicsPanel gp){ 
    for (int n = 1; n <= 150; n++)  {
        gp.clear();
        drawCircleOfPolygons(gp);
        gp.render();        
        gp.delay(30);       
        gp.turn(2);
    }
}

public static void drawCircleOfPolygons(GraphicsPanel gp){
    for (int angle = 0; angle < 360; angle += 10) {
        drawPolygon(gp, 100, 4);
        gp.turn(10);
    }
}

public static void drawPolygon(GraphicsPanel gp, int sideLength, int sideCount){
    for (int i = 0; i < sideCount; i++)  {
        gp.draw(sideLength);
        gp.turn(360.0 / sideCount);
        gp.delay(30);
    }
}
}

I have looked everywhere for an answer to no avail, can anybody please help me understand what I am doing wrong.

Answer 1

I've had a quick read through you code...

Don't...

• Don't override setSize of JPanel wihtout calling super.setSize , doing so will have dire consequences for how your component will work
• You MUST always call super.paintComponent regardless of what you are doing in the method, paintComponent does important work and this will result in numerous paint artifacts been left on you component and/or other paint related issues
• Avoid creating a JFrame within a component's constructor, this makes assumptions about the use of the component which aren't healthy. You component should make no assumption about how it might be used.
• Beware that components already have a concept of location and size, you should avoid from maintaining your own details, this leads to confusion over what you think the state is and what the actual state is...
• Your delay methods scares me. Swing is not thread safe and all interactions with the UI should always be made from within the context of the EDT. You should also never block the EDT, doing so will prevent from processing, amongst other things, repaint requests

My professor supplied us class GraphicsPanel

With all due respect, your professor has absolutely no idea what they are talking about, this is a series of rudimentary bad ideas and problems waiting to happen.

Your core problem is, Swing is a single threaded framework. This means that your for loop which you draw and rotate is been executed within the context of the EDT (in fact, it's likely that the component hasn't even been put on the screen yet), which means that until you exit the method, none of the paint events generated by your code can be processed.

The RepaintManager , responsible for scheduling paint events is always highly optimized, meaning that it is capable of coalescing multiple repaint requests into only a few actually events

Also, remember, transformation will only affect what is painted after it, not before. Therefore, rotation must be done before you do any painting in order for it take affect

Take a look at Concurrency in Swing , Performing Custom Painting , Painting in AWT and Swing , 2D Graphics and Creating a GUI With JFC/Swing for more details

Answer 2

Not really sure if I understand your issue fully, but if it is that the second example code G7 doesn't appear to be animated (like the first) as it turns slower than in the first example code GTest2 it's because you have duplicated the delay: gp.delay(30); in the second code; it appears both in the animateCircleOfPolygons function as well as in the drawPolygon function. It you remove either the code will produce identical output (as it should - it's the same logic after all).