"I want to draw a line, and it will highlight when I click it."

Question

I am currently working on a project right now. My project is a structural analysis software for civil engineers. Our project is already at it's infant
stage of development. I am having trouble with how to implement drawing on a canvas. Heres the specs:
-There are nodes on the drawing board illustrated by dots.
-Lines must be drawn connecting the nodes.
-Nodes must be a separate object where it could respond to mouse
events.
-Lines must also be a separate object where it could respond to mouse
events.
-Nodes and lines contain mathematical attributes, color information.
-I can instantly delete a line, or change its attributes by selecting
it.
Heres what I have imagined:
-I am going to draw my Nodes in a JPanel which implements a
mouseListener.
-Whenever I want to add nodes to the drawing board, I only have to add
the Node objects i created.
No problem with the nodes. Problem is in the lines i will be drawingconnecting one node to another.
-I tried manual live drawing of the lines as the mouse moves. Now its
flat on the drawing board. It can't be touched!
-I still don't have any idea how to implement the line that it could
respond to mouse events.
-If I try to draw it in a JPanel with mouseListener, a JPanel is square
so if I move my mouse to point in to the line drawn on the JPanel, it
will already respond before the mouse could reach the line image. One
thing also, it could overlap other JPanels.
-The JPanel idea came up to my mind coz I thought these objects could
be
selectable custom components.
-Now I realized JPanel is not the ANSWER!
In simple saying:
"I want to draw a line, and it will highlight when I click it."
Stubborn Newbie,
Edgar

Answer 1

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
public class SelectingLines extends JPanel
    Line2D.Double[] lines;
    int selectedIndex = -1;
    protected void paintComponent(Graphics g)
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        if(lines == null)
            initLines();
        for(int j = 0; j < lines.length; j++)
            Color color = Color.blue;
            if(j == selectedIndex)
                color = Color.green.darker();
            g2.setPaint(color);
            g2.draw(lines[j]);
    public void setSelection(int index)
        selectedIndex = index;
        repaint();
    private void initLines()
        lines = new Line2D.Double[3];
        int w = getWidth();
        int h = getHeight();
        lines[0] = new Line2D.Double(w/8, h/8, w/3, h/6);
        lines[1] = new Line2D.Double(w/3, h/6, w/2, h/2);
        lines[2] = new Line2D.Double(w/2, h/2, w*5/8, h*7/12);
    public static void main(String[] args)
        SelectingLines selectPanel = new SelectingLines();
        selectPanel.addMouseListener(new LineSelector(selectPanel));
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(selectPanel);
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
class LineSelector extends MouseAdapter
    SelectingLines selectingLines;
    Rectangle r;
    final int S = 4;
    public LineSelector(SelectingLines sl)
        selectingLines = sl;
        r = new Rectangle(S, S);
    public void mousePressed(MouseEvent e)
        Point p = e.getPoint();
        r.setLocation(p.x-S/2, p.y-S/2);
        Line2D.Double[] lines = selectingLines.lines;
        int index = -1;
        for(int j = 0; j < lines.length; j++)
            if(lines[j].intersects(r))
                index = j;
                break;
        if(index != selectingLines.selectedIndex)
            selectingLines.setSelection(index);
}