Translate a circle component

[tom davies]

I am trying to centre a circle component i have created. I think my method of calculating the correct co ordinates is right, but when i try to translate using the new co ordinates i get an error saying
cannot find symbol
symbol: Method translate(double,double)
location: variable circle of type Double

import java.awt.*;
import java.awt.geom.Ellipse2D;
import javax.swing.*;
public class EllipseComponent extends JComponent
{
    
    public void paintComponent(Graphics g)
    {
        Graphics2D g2 = (Graphics2D) g;
        
        Ellipse2D.Double circle = new Ellipse2D.Double(0, 0, 400, 400);
        
        double x = (this.getWidth()-circle.getWidth())/2;
        double y= (this.getHeight()-circle.getWidth()/2);
        
        circle.translate(x, y);

    }
    
}

[Jesper de Jong]

Your variable circle has the type java.awt.geom.Ellipse2D.Double. When I look that class up in the API documentation, I don't see that it has a method translate(). The compiler is complaining that that method doesn't exist.

[Kemal Sokolovic]

There is not method translate for the type you are using, hence the error.
You can first calculate the position where your ellipse is to be drawn and then draw it (no need for changing). By the way, the code for calculating y coordinate of the center is not correct.

[tom davies]

Thanks, had a re-think and decided to make the height/width a percentage of the JComponent size.
Is this the most efficient way to do it or have i made more work for myself than needed?

import java.awt.*;
import java.awt.geom.Ellipse2D;
import javax.swing.*;
public class EllipseComponent extends JComponent
{
    
    public void paintComponent(Graphics g)
    {
        Graphics2D g2 = (Graphics2D) g;
        
        double circleWidth = this.getWidth()/100*80;
        double circleHeight = this.getHeight()/100*80;
        
        double x = (this.getWidth()-circleWidth)/2;
        double y= (this.getHeight()-circleHeight)/2;
        
        Ellipse2D.Double circle = new Ellipse2D.Double(x, y, circleWidth, circleHeight);

        g2.draw(circle);

    }
    
}

[Campbell Ritchie]

I shall move you to our GUIs forum.
There is in fact an object around which has a translate() method, but it aint’t the circle. It’s the Graphics object. Look here and search/Google for affine transforms. I suggest you copy the Graphics object; some affine transforms can alter the object in such a way that you can never return it to its original state. You also need to cast it to Graphics2D. Something like this might work.

protected /*not public*/ void paintComponent(Graphics g)
{
    super.paintComponent(g); // This line is important
    Graphics2D g2 = (Graphics2D) g.create;
    g2.translate(12, 34);
    // etc
}

Read the documentation carefully; that doesn’t mean 12 right and 34 up.