source: josm/src/org/openstreetmap/josm/data/osm/visitor/SelectionComponentVisitor.java@ 71

package org.openstreetmap.josm.data.osm.visitor;

import java.util.HashSet;
import java.util.Set;

import javax.swing.Icon;

import org.openstreetmap.josm.data.osm.LineSegment;
import org.openstreetmap.josm.data.osm.Node;
import org.openstreetmap.josm.data.osm.Way;
import org.openstreetmap.josm.tools.ImageProvider;

/**
 * Able to create a name and an icon for each data element.
 * 
 * @author imi
 */
public class SelectionComponentVisitor implements Visitor {

        /**
         * The name of this item.
         */
        public String name;
        /**
         * The icon of this item.
         */
        public Icon icon;
        
        
        /**
         * If the line segment has a key named "name", its value is displayed. 
         * Otherwise, if it has "id", this is used. If none of these available, 
         * "(x1,y1) -> (x2,y2)" is displayed with the nodes coordinates.
         */
        public void visit(LineSegment ls) {
                name = ls.get("name");
                if (name == null) {
                        if (ls.incomplete)
                                name = ""+ls.id;
                        else
                                name = ls.id+" ("+ls.from.coor.lat()+","+ls.from.coor.lon()+") -> ("+ls.to.coor.lat()+","+ls.to.coor.lon()+")";
                }
                icon = ImageProvider.get("data", "linesegment");
        }

        /**
         * If the node has a name-key or id-key, this is displayed. If not, (lat,lon)
         * is displayed.
         */
        public void visit(Node n) {
                name = n.get("name");
                if (name == null)
                        name = n.id+" ("+n.coor.lat()+","+n.coor.lon()+")";
                icon = ImageProvider.get("data", "node");
        }

        /**
         * If the way has a name-key or id-key, this is displayed. If not, (x nodes)
         * is displayed with x beeing the number of nodes in the way.
         */
        public void visit(Way w) {
                name = w.get("name");
                if (name == null) {
                        AllNodesVisitor.getAllNodes(w.segments);
                        Set<Node> nodes = new HashSet<Node>();
                        for (LineSegment ls : w.segments) {
                                if (!ls.incomplete) {
                                        nodes.add(ls.from);
                                        nodes.add(ls.to);
                                }
                        }
                        name = "("+nodes.size()+" nodes)";
                }
                icon = ImageProvider.get("data", "way");
        }
}