将图像置于面板中间

Question

我正在研究Java中的Graphics并在JPanel上创建一个圆圈.如何在JPanel中圈出圆圈？

package exerciseninetwo;
import javax.swing.*;
import java.awt.*;
import java.awt.geom.Ellipse2D;    

public class ExerciseNineTwo extends JFrame
{
    public ExerciseNineTwo()
    {
        super("My Frame");
        setSize(500, 500);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        add(new CanvasPanel());

        setVisible(true);        
    }        

    public static void main(String[] args)
    {
        new ExerciseNineTwo();
    }
}
class CanvasPanel extends JPanel
{        
    CanvasPanel()
    {
        setSize(120, 120);            
        //setBackground(Color.cyan);
    }

    protected void paintComponent(Graphics g)
    {
        Graphics2D comp = (Graphics2D)g;
        Ellipse2D circle = new Ellipse2D.Float(200, 200, 200, 200);
        comp.draw(circle);

        comp.setColor(Color.cyan);
        comp.fillRect(0,0,500,500);

        comp.setClip(circle);
        comp.setColor(Color.magenta);
        comp.fillRect(0,0,500,500);           
    }
}

Answer 1

只需在面板中间绘制它.

float x = getWidth()/2 - ELLIPSE_WIDTH/2;
float y = getHeight()/2 - ELLIPSE_HEIGHT/2;
Ellipse2D circle = new Ellipse2D.Float(x, y, ELLIPSE_WIDTH, ELLIPSE_HEIGHT);