source: josm/src/org/openstreetmap/josm/data/osm/LineSegment.java@ 8

package org.openstreetmap.josm.data.osm;

import java.util.Collection;
import java.util.Collections;
import java.util.LinkedList;

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


/**
 * One track line segment consisting of a pair of nodes (start/end) 
 *
 * @author imi
 */
public class LineSegment extends OsmPrimitive {

        /**
         * The starting node of the line segment
         */
        private Node start;
        
        /**
         * The ending node of the line segment
         */
        private Node end;

        /**
         * The tracks, this line segment is part of.
         */
        transient Collection<Track> parent = new LinkedList<Track>();

        /**
         * Create an line segment from the given starting and ending node
         * @param start Starting node of the line segment.
         * @param end   Ending node of the line segment.
         */
        public LineSegment(Node start, Node end) {
                this.start = start;
                this.end = end;
                start.parentSegment.add(this);
                end.parentSegment.add(this);
        }

        /**
         * Return all parent tracks this line segment is part of. The list is readonly.
         */
        public Collection<Track> getParents() {
                return Collections.unmodifiableCollection(parent);
        }

        public void setStart(Node start) {
                this.start.parentSegment.remove(this);
                this.start = start;
                start.parentSegment.add(this);
        }
        public Node getStart() {
                return start;
        }
        public void setEnd(Node end) {
                this.end.parentSegment.remove(this);
                this.end = end;
                end.parentSegment.add(this);
        }
        public Node getEnd() {
                return end;
        }

        /**
         * The LineSegment is going to be destroyed. Unlink all back references.
         */
        void destroy() {
                start.parentSegment.remove(this);
                end.parentSegment.remove(this);
        }

        /**
         * Return start and end in a list.
         */
        @Override
        public Collection<Node> getAllNodes() {
                LinkedList<Node> nodes = new LinkedList<Node>();
                nodes.add(getStart());
                nodes.add(getEnd());
                return nodes;
        }

        /**
         * Line segments are equal, if their starting and ending node and their
         * keys are equal.
         */
        @Override
        public boolean equals(Object obj) {
                if (!(obj instanceof LineSegment))
                        return false;
                return super.equals(obj) && 
                        getStart().equals(((LineSegment)obj).getStart()) &&
                        getEnd().equals(((LineSegment)obj).getEnd());
        }

        @Override
        public int hashCode() {
                return super.hashCode() + getStart().hashCode() + getEnd().hashCode();
        }

        @Override
        public void visit(Visitor visitor) {
                visitor.visit(this);
        }
}