好的，基本上，我们可以将问题分解为基本问题：

1. 获取两个圆之间的角度
2. 从这个圆的圆周到另一个圆的圆周画一条线
   这两个问题都不难解决（而且花在
   互联网上的任何时间都会提供解决方案-因为那是我从中获得的；））
   

因此，两点之间的角度可以使用类似…的方法来计算

protected double angleBetween(Point2D from, Point2D to) {    double x = from.getX();    double y = from.getY();    // This is the difference between the anchor point    // and the mouse.  Its important that this is done    // within the local coordinate space of the component,    // this means either the MouseMotionListener needs to    // be registered to the component itself (preferably)    // or the mouse coordinates need to be converted into    // local coordinate space    double deltaX = to.getX() - x;    double deltaY = to.getY() - y;    // Calculate the angle...    // This is our "0" or start angle..    double rotation = -Math.atan2(deltaX, deltaY);    rotation = Math.toRadians(Math.toDegrees(rotation) + 180);    return rotation;}

And the point on a circle can be calculated using something like…

protected Point2D getPointonCircle(Point2D center, double radians, double radius) {    double x = center.getX();    double y = center.getY();    radians = radians - Math.toRadians(90.0); // 0 becomes the top    // Calculate the outter point of the line    double xPosy = Math.round((float) (x + Math.cos(radians) * radius));    double yPosy = Math.round((float) (y + Math.sin(radians) * radius));    return new Point2D.Double(xPosy, yPosy);}

请注意，对结果进行了一些内部修改，以允许数学解决方案与

GraphicsAPI

好的，您说的这么多，对我有什么帮助？好吧，我实际上很棒。

您可以计算到的圆之间的角度（来回之间，也许
可以简单地将一个角度反演，但是我有可用的计算方法，所以我
使用了它）。由此，您可以计算线将
在其上相交的每个圆的点，然后只需要绘制它，就像…

double from = angleBetween(circle1, circle2);double to = angleBetween(circle2, circle1);Point2D pointFrom = getPointonCircle(circle1, from);Point2D pointTo = getPointonCircle(circle2, to);Line2D line = new Line2D.Double(pointFrom, pointTo);g2d.draw(line);

可运行的例子

因为我将许多计算精简为公用属性，所以提供了测试代码作为可运行示例。所有的
计算都是基于动态值，没有什么是真正的硬编码。对于例如，你可以改变大小和圆的位置和计算应该继续工作......

import java.awt.Color;import java.awt.Dimension;import java.awt.EventQueue;import java.awt.Graphics;import java.awt.Graphics2D;import java.awt.Shape;import java.awt.geom.Ellipse2D;import java.awt.geom.Line2D;import java.awt.geom.Point2D;import java.awt.geom.Rectangle2D;import javax.swing.Jframe;import javax.swing.JPanel;import javax.swing.UIManager;import javax.swing.UnsupportedLookAndFeelException;public class Test {    public static void main(String[] args) {        new Test();    }    public Test() {        EventQueue.invokeLater(new Runnable() { @Override public void run() {     try {         UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());     } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {         ex.printStackTrace();     }     Jframe frame = new Jframe("Testing");     frame.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);     frame.add(new TestPane());     frame.pack();     frame.setLocationRelativeTo(null);     frame.setVisible(true); }        });    }    public class TestPane extends JPanel {        private Ellipse2D circle1;        private Ellipse2D circle2;        private Point2D drawTo;        public TestPane() { circle1 = new Ellipse2D.Double(10, 10, 40, 40); circle2 = new Ellipse2D.Double(100, 150, 40, 40); //addMouseMotionListener(new MouseAdapter() { //  @Override //  public void mouseMoved(MouseEvent e) { //      drawTo = new Point2D.Double(e.getPoint().x, e.getPoint().y); //      repaint(); //  } //});        }        protected Point2D center(Rectangle2D bounds) { return new Point2D.Double(bounds.getCenterX(), bounds.getCenterY());        }        protected double angleBetween(Shape from, Shape to) { return angleBetween(center(from.getBounds2D()), center(to.getBounds2D()));        }        protected double angleBetween(Point2D from, Point2D to) { double x = from.getX(); double y = from.getY(); // This is the difference between the anchor point // and the mouse.  Its important that this is done // within the local coordinate space of the component, // this means either the MouseMotionListener needs to // be registered to the component itself (preferably) // or the mouse coordinates need to be converted into // local coordinate space double deltaX = to.getX() - x; double deltaY = to.getY() - y; // Calculate the angle... // This is our "0" or start angle.. double rotation = -Math.atan2(deltaX, deltaY); rotation = Math.toRadians(Math.toDegrees(rotation) + 180); return rotation;        }        protected Point2D getPointonCircle(Shape shape, double radians) { Rectangle2D bounds = shape.getBounds();//          Point2D point = new Point2D.Double(bounds.getX(), bounds.getY()); Point2D point = center(bounds); return getPointonCircle(point, radians, Math.max(bounds.getWidth(), bounds.getHeight()) / 2d);        }        protected Point2D getPointonCircle(Point2D center, double radians, double radius) { double x = center.getX(); double y = center.getY(); radians = radians - Math.toRadians(90.0); // 0 becomes th?e top // Calculate the outter point of the line double xPosy = Math.round((float) (x + Math.cos(radians) * radius)); double yPosy = Math.round((float) (y + Math.sin(radians) * radius)); return new Point2D.Double(xPosy, yPosy);        }        @Override        public Dimension getPreferredSize() { return new Dimension(200, 200);        }        protected void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g.create(); g2d.draw(circle1); g2d.draw(circle2); // This was used for testing, it will draw a line from circle1 to the // drawTo point, which, if enabled, is the last known position of the // mouse //if (drawTo != null) { //  Point2D pointFrom = center(circle1.getBounds2D()); //  g2d.setColor(Color.RED); //  g2d.draw(new Line2D.Double(drawTo, pointFrom)); // //  double from = angleBetween(pointFrom, drawTo); //  System.out.println(NumberFormat.getNumberInstance().format(Math.toDegrees(from))); // //  Point2D poc = getPointonCircle(circle1, from); //  g2d.setColor(Color.BLUE); //  g2d.draw(new Line2D.Double(poc, drawTo)); //} double from = angleBetween(circle1, circle2); double to = angleBetween(circle2, circle1); Point2D pointFrom = getPointonCircle(circle1, from); Point2D pointTo = getPointonCircle(circle2, to); g2d.setColor(Color.RED); Line2D line = new Line2D.Double(pointFrom, pointTo); g2d.draw(line); g2d.dispose();        }    }}

Arrow head

The intention is to treat the arrow head as a separate entity. The reason is
because it’s just simpler that way, you also get a more consistent result
regardless of the distance between the objects.

So, to start with, I define a new

Shape

public class ArrowHead extends Path2D.Double {    public ArrowHead() {        int size = 10;        moveTo(0, size);        lineTo(size / 2, 0);        lineTo(size, size);    }}

Pretty simple really. It just creates two lines, which point up, meeting in
the middle of the available space.

Then in the

paintComponent

AffineTransform

• The point on our target circles circumference
• The angle to our target circle

And transform the

ArrowHead

g2d.setColor(Color.MAGENTA);ArrowHead arrowHead = new ArrowHead();AffineTransform at = AffineTransform.getTranslateInstance(     pointTo.getX() - (arrowHead.getBounds2D().getWidth() / 2d),      pointTo.getY());at.rotate(from, arrowHead.getBounds2D().getCenterX(), 0);arrowHead.transform(at);g2d.draw(arrowHead);

Now, because I’m crazy, I also tested the pre by drawing an arrow pointing at
our source circle, just to prove that the calculations would work…

// This just proofs that the previous calculations weren't a fluke// and that the arrow can be painted pointing to the source object as wellg2d.setColor(Color.GREEN);arrowHead = new ArrowHead();at = AffineTransform.getTranslateInstance(     pointFrom.getX() - (arrowHead.getBounds2D().getWidth() / 2d),      pointFrom.getY());at.rotate(to, arrowHead.getBounds2D().getCenterX(), 0);arrowHead.transform(at);g2d.draw(arrowHead);