source: josm/src/org/openstreetmap/josm/data/osm/visitor/SelectionComponentVisitor.java@ 21

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

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

import javax.swing.Icon;

import org.openstreetmap.josm.data.osm.Key;
import org.openstreetmap.josm.data.osm.LineSegment;
import org.openstreetmap.josm.data.osm.Node;
import org.openstreetmap.josm.data.osm.Track;
import org.openstreetmap.josm.gui.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;
        
        
        /**
         * A key icon and the name of the key.
         */
        public void visit(Key k) {
                name = k.name;
                icon = ImageProvider.get("data", "key");
        }

        /**
         * 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) {
                String name = getName(ls.keys);
                if (name == null)
                        name = "("+ls.getStart().coor.lat+","+ls.getStart().coor.lon+") -> ("+ls.getEnd().coor.lat+","+ls.getEnd().coor.lon+")";
                        
                this.name = name;
                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) {
                String name = getName(n.keys);
                if (name == null)
                        name = "("+n.coor.lat+","+n.coor.lon+")";
                
                this.name = name;
                icon = ImageProvider.get("data", "node");
        }

        /**
         * If the track 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 track.
         */
        public void visit(Track t) {
                String name = getName(t.keys);
                if (name == null) {
                        Set<Node> nodes = new HashSet<Node>();
                        for (LineSegment ls : t.segments()) {
                                nodes.add(ls.getStart());
                                nodes.add(ls.getEnd());
                        }
                        name = "("+nodes.size()+" nodes)";
                }
                
                this.name = name;
                icon = ImageProvider.get("data", "track");
        }

        
        /**
         * Try to read a name from the given properties.
         * @param keys The properties to search for a name. Can be <code>null</code>.
         * @return If a name could be found, return it here.
         */
        public String getName(Map<Key, String> keys) {
                String name = null;
                if (keys != null) {
                        name = keys.get(Key.get("name"));
                        if (name == null)
                                name = keys.get(Key.get("id"));
                }
                return name;
        }
        
}