Question

Java Programing.

Using NetBean

Write a program to draw a line connecting two circles. These two circles can be dragged by mouse. And when circles are dragged, the line should be adjusted so that it still connect these two circles (binding property)

Answer 1

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();
}

}

}