Java图形绘制具有特定参数的圆圈

Question

对于一个问题，我必须在屏幕上画一个圆，中心位于坐标（280,300），半径为50.提示说：圆是一个宽度和高度相同的椭圆。该圆圈的中心位于此椭圆形NW角的右下方50像素和50像素处。

有TryoutPanel类：

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

public class TryoutPanel extends JPanel{

  private Color myColor;

  public TryoutPanel(Color c){
    myColor = c;
  }

  public void paintComponent(Graphics g){
    super.paintComponent(g);
    setForeground(myColor);
    g.drawString("top",10,50);
    g.drawLine(10,60, 200,60);
    g.drawString("middle",10,80);
    g.drawLine(10,90, 200,90);
    g.drawString("bottom",10,110);
    g.drawLine(10,120, 200,120);
    g.drawRect(200,300,100,50);
    g.drawOval(200,300,100,50);
    for(int j = 0; j < 9; j++)
      g.drawOval(50,200, 10 + 20*j, 210 - 20*j);
  }
}

我必须填写以下代码：

public void paintComponent(Graphics g){
  super.paintComponent(g);
  setForeground(myColor);
  //INSERT CODE HERE

我试过了：     g.drawOval(280,300,50,50);

但它说我使用了不正确的参数。我做错了什么。

Answer 1

x的{​​{1}} / y参数是绘制椭圆的上/左角

为了能够在drawOval处围绕中心点绘制圆，您需要从每个点中减去半径，然后生成双倍的宽度和高度（直径）... < / p>

230x300

因此，此示例基本围绕g.drawOval(230 - radius, 300 - radius, radius * 2, radius * 2); 的点绘制一个矩形，宽度/高度为230x300（半径= 100），并通过此点绘制线条以说明椭圆的中心点然后关于......

200

哦，import java.awt.BorderLayout; import java.awt.Color; import java.awt.Dimension; import java.awt.EventQueue; import java.awt.Graphics; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.UIManager; import javax.swing.UnsupportedLookAndFeelException; public class TryoutOval { public static void main(String[] args) { new TryoutOval(); } public TryoutOval() { EventQueue.invokeLater(new Runnable() { @Override public void run() { try { UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { } JFrame frame = new JFrame("Testing"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setLayout(new BorderLayout()); frame.add(new TryoutPanel(Color.RED)); frame.pack(); frame.setLocationRelativeTo(null); frame.setVisible(true); } }); } public class TryoutPanel extends JPanel { private Color myColor; public TryoutPanel(Color c) { myColor = c; } @Override public Dimension getPreferredSize() { return new Dimension(400, 400); } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); int centerX = 280; int centerY = 300; int radius = 50; int diameter = radius * 2; int x = centerX - radius; int y = centerY - radius; g.setColor(Color.BLACK); g.drawRect(x, y, diameter, diameter); g.drawLine(x, y, x + diameter, y + diameter); g.drawLine(x + diameter, y, x, y + diameter); g.setColor(myColor); g.drawOval(x, y, diameter, diameter); g.fillOval(centerX - 5, centerY - 5, 10, 10); } } } 在任何setForeground(myColor);方法中都是一个非常糟糕的主意，因为每次调用该方法时都会导致paint事件被添加到事件队列中，将导致一个永无止境的重绘请求，最终消耗你的CPU