source: josm/src/org/openstreetmap/josm/actions/mapmode/AddNodeAction.java@ 98

package org.openstreetmap.josm.actions.mapmode;

import java.awt.event.KeyEvent;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.LinkedList;

import javax.swing.JOptionPane;

import org.openstreetmap.josm.Main;
import org.openstreetmap.josm.actions.GroupAction;
import org.openstreetmap.josm.command.AddCommand;
import org.openstreetmap.josm.command.ChangeCommand;
import org.openstreetmap.josm.command.Command;
import org.openstreetmap.josm.command.SequenceCommand;
import org.openstreetmap.josm.data.osm.Node;
import org.openstreetmap.josm.data.osm.Segment;
import org.openstreetmap.josm.data.osm.Way;
import org.openstreetmap.josm.gui.MapFrame;

/**
 * This mode adds a new node to the dataset. The user clicks on a place to add
 * and there is it. Nothing more, nothing less.
 * 
 * Newly created nodes are selected. Shift modifier does not cancel the old 
 * selection as usual.
 * 
 * @author imi
 *
 */
public class AddNodeAction extends MapMode {

        enum Mode {node, nodesegment}
        private final Mode mode;

        public static class AddNodeGroup extends GroupAction {
                public AddNodeGroup(MapFrame mf) {
                        super(KeyEvent.VK_N,0);
                        actions.add(new AddNodeAction(mf, "Add node", Mode.node, "Add a new node to the map"));
                        actions.add(new AddNodeAction(mf, "Add node into segment", Mode.nodesegment, "Add a node into an existing segment"));
                        setCurrent(0);
                }
        }

        public AddNodeAction(MapFrame mapFrame, String name, Mode mode, String desc) {
                super(name, "node/"+mode, desc, mapFrame);
                this.mode = mode;
        }

        @Override public void enterMode() {
                super.enterMode();
                Main.map.mapView.addMouseListener(this);
        }

        @Override public void exitMode() {
                super.exitMode();
                Main.map.mapView.removeMouseListener(this);
        }

        /**
         * If user clicked with the left button, add a node at the current mouse
         * position.
         * 
         * If in nodesegment mode, add the node to the line segment by splitting the
         * segment. The new created segment will be inserted in every way the segment
         * was part of.
         */
        @Override public void mouseClicked(MouseEvent e) {
                if (e.getButton() != MouseEvent.BUTTON1)
                        return;

                Node n = new Node(Main.map.mapView.getLatLon(e.getX(), e.getY()));
                if (n.coor.isOutSideWorld()) {
                        JOptionPane.showMessageDialog(Main.parent, "Can not add a node outside of the world.");
                        return;
                }

                Command c = new AddCommand(n);
                if (mode == Mode.nodesegment) {
                        Segment s = Main.map.mapView.getNearestSegment(e.getPoint());
                        if (s == null)
                                return;

                        Collection<Command> cmds = new LinkedList<Command>();
                        cmds.add(c);
                        Segment s1 = new Segment(s);
                        s1.to = n;
                        Segment s2 = new Segment(s.from, s.to);
                        s2.from = n;
                        if (s.keys != null)
                                s2.keys = new HashMap<String, String>(s.keys);

                        cmds.add(new ChangeCommand(s, s1));
                        cmds.add(new AddCommand(s2));

                        // Add the segment to every way
                        for (Way wold : Main.ds.ways) {
                                if (wold.segments.contains(s)) {
                                        Way wnew = new Way(wold);
                                        Collection<Segment> segs = new ArrayList<Segment>(wnew.segments);
                                        wnew.segments.clear();
                                        for (Segment waySeg : segs) {
                                                wnew.segments.add(waySeg);
                                                if (waySeg == s)
                                                        wnew.segments.add(s2);
                                        }
                                        cmds.add(new ChangeCommand(wold, wnew));
                                }
                        }

                        c = new SequenceCommand(cmds);
                }
                Main.main.editLayer().add(c);
                Main.map.mapView.repaint();
        }
}