source: josm/src/org/openstreetmap/josm/data/osm/OsmPrimitive.java@ 22

package org.openstreetmap.josm.data.osm;

import java.util.Collection;
import java.util.Map;

import org.openstreetmap.josm.Main;
import org.openstreetmap.josm.data.osm.visitor.Visitor;


/**
 * An OSM primitive can be associated with a key/value pair. It can be created, deleted
 * and updated within the OSM-Server.
 * 
 * @author imi
 */
abstract public class OsmPrimitive {

        /**
         * The key/value list for this primitive.
         */
        public Map<Key, String> keys;
        
        /**
         * If set to true, this object has been modified in the current session.
         */
        transient public boolean modified = false;
        
        /**
         * If set to true, this object is currently selected.
         */
        transient private boolean selected = false;

        /**
         * Return a list of all nodes, this osmPrimitive consists of. Does return
         * an empty list, if it is an primitive that cannot have nodes (e.g. Key)
         * TODO replace with visitor
         */
        abstract public Collection<Node> getAllNodes();

        /**
         * Implementation of the visitor scheme. Subclases have to call the correct
         * visitor function.
         * @param visitor The visitor from which the visit() function must be called.
         */
        abstract public void visit(Visitor visitor);
        
        /**
         * Return <code>true</code>, if either <code>this.keys</code> and 
         * <code>other.keys</code> is <code>null</code> or if they do not share Keys
         * with different values.
         *  
         * @param other         The second key-set to compare with.
         * @return      True, if the keysets are mergable
         */
        public boolean keyPropertiesMergable(OsmPrimitive other) {
                if ((keys == null) != (other.keys == null))
                        return false;

                if (keys != null) {
                        for (Key k : keys.keySet())
                                if (other.keys.containsKey(k) && !keys.get(k).equals(other.keys.get(k)))
                                        return false;
                        for (Key k : other.keys.keySet())
                                if (keys.containsKey(k) && !other.keys.get(k).equals(keys.get(k)))
                                        return false;
                }
                return true;
        }

        /**
         * Mark the primitive as selected or not selected and fires a selection 
         * changed later, if the value actualy changed.
         * @param selected Whether the primitive should be selected or not.
         */
        public void setSelected(boolean selected) {
                if (selected != this.selected)
                        Main.main.ds.fireSelectionChanged();
                this.selected = selected;
        }

        /**
         * @return Return whether the primitive is selected on screen.
         */
        public boolean isSelected() {
                return selected;
        }
}