How to translate the use of Java (Swing) internal classes in JRuby code http://stackoverflow.com/questions/21245604/how-to-translate-the-use-of-java-internal-classes-in-jruby-code

mouse_test.rb

frame = javax.swing.JFrame.new
frame.title = "MouseTest"
frame.set_size(300, 200)
frame.add_window_listener do |evt|
  if evt.getID == java.awt.event.WindowEvent::WINDOW_CLOSING
    java.lang.System.exit(0)
  end
end

class MousePanel < Java::JavaxSwing::JPanel

  java_import java.awt.Cursor

  SQUARELENGTH = 10; MAXNSQUARES = 100;

  def initialize
    super
    @squares = []; @size = 0; @current = nil
    add_mouse_listener self
    add_mouse_motion_listener self
  end

  def add(x, y)
    if @squares.size < MAXNSQUARES
       @current = @squares.size
       @squares << Point.new(x, y)
       repaint
    end
  end

  def remove(n = @current)
    return if n < 0 || n >= @squares.size
    @squares.pop
    @squares[n] = @squares[@squares.size]
    @current = nil if @current == n
    repaint
  end

  def paintComponent(graphics)
    super
    @squares.each { |square| draw_square(graphics, square) }
  end

  include java.awt.event.MouseListener

  [ 'mouseEntered', 'mouseExited', 'mouseReleased' ].each do |method|
    class_eval "def #{method}(evt); end"
  end

  def mousePressed(evt)
    x = evt.getX; y = evt.getY
    add(x, y) unless find_square(x, y)
  end

  def mouseClicked(evt)
    remove if evt.click_count >= 2
  end

  include java.awt.event.MouseMotionListener

  def mouseMoved(evt)
    if find_square(evt.getX, evt.getY)
      setCursor Cursor.getPredefinedCursor(Cursor::CROSSHAIR_CURSOR)
    else
      setCursor Cursor.getDefaultCursor()
    end
  end

  def mouseDragged(evt)
    return unless @current
    graphics = self.graphics
    graphics.setXORMode background
    square = @squares[ @current ]
    draw_square(graphics, square)
    square.x = evt.getX
    square.y = evt.getY
    draw_square(graphics, square)
    graphics.dispose
  end

  private

  def draw_square(graphics, square)
    graphics.drawRect(
      square.x - SQUARELENGTH / 2,
      square.y - SQUARELENGTH / 2,
      SQUARELENGTH, SQUARELENGTH
    )
  end

  def find_square(x, y)
    @squares.each do |square|
      if (square.x - SQUARELENGTH / 2 <= x &&
        x <= square.x + SQUARELENGTH / 2 &&
        square.y - SQUARELENGTH / 2 <= y &&
        y <= square.y + SQUARELENGTH / 2)
        return square
      end
    end
    nil
  end

end

frame.content_pane.add MousePanel.new
frame.show

MouseTest.java

/**
 * @version 1.20 25 Mar 1998
 * @author Cay Horstmann
 */
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

class MousePanel extends JPanel implements MouseMotionListener {

    public MousePanel() {
        addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent evt) {
                int x = evt.getX();
                int y = evt.getY();
                current = find(x, y);
                if (current < 0) // not inside a square
                {
                    add(x, y);
                }
            }

            public void mouseClicked(MouseEvent evt) {
                int x = evt.getX();
                int y = evt.getY();

                if (evt.getClickCount() >= 2) {
                    remove(current);
                }
            }
        });
        addMouseMotionListener(this);
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        for (int i = 0; i < nsquares; i++) {
            draw(g, i);
        }
    }

    public int find(int x, int y) {
        for (int i = 0; i < nsquares; i++) {
            if (squares[i].x - SQUARELENGTH / 2 <= x
                    && x <= squares[i].x + SQUARELENGTH / 2
                    && squares[i].y - SQUARELENGTH / 2 <= y
                    && y <= squares[i].y + SQUARELENGTH / 2) {
                return i;
            }
        }
        return -1;
    }

    public void draw(Graphics g, int i) {
        g.drawRect(squares[i].x - SQUARELENGTH / 2,
                squares[i].y - SQUARELENGTH / 2,
                SQUARELENGTH,
                SQUARELENGTH);
    }

    public void add(int x, int y) {
        if (nsquares < MAXNSQUARES) {
            squares[nsquares] = new Point(x, y);
            current = nsquares;
            nsquares++;
            repaint();
        }
    }

    public void remove(int n) {
        if (n < 0 || n >= nsquares) {
            return;
        }
        nsquares--;
        squares[n] = squares[nsquares];
        if (current == n) {
            current = -1;
        }
        repaint();
    }

    public void mouseMoved(MouseEvent evt) {
        int x = evt.getX();
        int y = evt.getY();

        if (find(x, y) >= 0) {
            setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));
        } else {
            setCursor(Cursor.getDefaultCursor());
        }
    }

    public void mouseDragged(MouseEvent evt) {
        int x = evt.getX();
        int y = evt.getY();

        if (current >= 0) {
            Graphics g = getGraphics();
            g.setXORMode(getBackground());
            draw(g, current);
            squares[current].x = x;
            squares[current].y = y;
            draw(g, current);
            g.dispose();
        }
    }
    private static final int SQUARELENGTH = 10;
    private static final int MAXNSQUARES = 100;
    private Point[] squares = new Point[MAXNSQUARES];
    private int nsquares = 0;
    private int current = -1;
}

class MouseFrame extends JFrame {

    public MouseFrame() {
        setTitle("MouseTest");
        setSize(300, 200);
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });

        Container contentPane = getContentPane();
        contentPane.add(new MousePanel());
    }
}

public class MouseTest {

    public static void main(String[] args) {
        JFrame frame = new MouseFrame();
        frame.show();
    }
    
}