Some more examples in Python:

Export a collection of routes to Garmin GPX file:

#!/bin/jython
'''
RWN2Garmin.py  - Numbered networks to Garmin GPX file converter
This code is released under the GNU General
Public License v2 or later.

The GPL v3 is accessible here:
http://www.gnu.org/licenses/gpl.html

The GPL v2 is accessible here:
http://www.gnu.org/licenses/old-licenses/gpl-2.0.html

It comes with no warranty whatsoever.

This code illustrates how to use Jython to:
* work with selected items or how to process all the primitives of a certain kind (node, way, relation)

'''
from javax.swing import JOptionPane, JDialog
from java.awt.event import ActionListener, ActionEvent
from org.openstreetmap.josm import Main
import org.openstreetmap.josm.command as Command
import org.openstreetmap.josm.data.osm.Node as Node
import org.openstreetmap.josm.data.osm.Way as Way
import org.openstreetmap.josm.data.osm.TagCollection as TagCollection
import org.openstreetmap.josm.data.osm.DataSet as DataSet
import time

def getMapView():
    if Main.main and Main.main.map:
        return Main.main.map.mapView
    else:
        return None

mv = getMapView()
f = open('C:/export.gpx', 'w')
f.write('<?xml version="1.0" encoding="UTF-8" standalone="yes"?>\n')
f.write('<gpx xmlns="http://www.topografix.com/GPX/1/1" creator="OSM Route Manager" version="1.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd">\n')
f.write('<!-- All data by OpenStreetMap, licensed under cc-by-sa-2.0 (http://creativecommons.org/licenses/by-sa/2.0/). -->\n')
if mv and mv.editLayer and mv.editLayer.data:
    #selectedNodes = mv.editLayer.data.getSelectedNodes()
    #selectedWays = mv.editLayer.data.getSelectedWays()
    selectedRelations = mv.editLayer.data.getSelectedRelations()

    if not(selectedRelations):
        JOptionPane.showMessageDialog(Main.parent, "Please select a collection relation")
    else:
        # nodetype = Node().getType()
        print
        for collection in selectedRelations:
            print 'COLLECTION:', collection
            for member in collection.getMembers():
                print 'MEMBER:',member
                if member.isNode():
                    node = member.getNode()
                    coords = node.getCoor()
                    lon = coords.getX()
                    lat = coords.getY()
                    rwn_ref = node.get('rwn_ref')
                    f.write('\t<wpt lat="' + str(lat) + '" lon="' + str(lon) + '">\n')
                    if rwn_ref:
                        f.write('\t\t<name>' + rwn_ref + '</name>\n')
                    f.write('\t</wpt>\n')
            for member in collection.getMembers():
                if member.isRelation():
                    routerelation = member.getRelation()
                    f.write('\t<trk>\n')
                    networkname =  routerelation.get('network:name')
                    if not(networkname):
                        networkname =  ''
                    else:
                        networkname += ' '
                    note = routerelation.get('note')
                    if not(note): note =  ''
                    f.write('\t\t<name>' + networkname + note + '</name>\n')
                    f.write('\t\t<src>OpenStreetMap.org</src>\n')
                    f.write('\t\t<type>foot</type>\n')
                    for routerelmember in routerelation.getMembers():
                        if routerelmember.isWay():
                            f.write('\t\t<trkseg>\n')
                            way=routerelmember.getWay()
                            for waynode in way.getNodes():
                                 coords = waynode.getCoor()
                                 lon = coords.getX()
                                 lat = coords.getY()
                                 f.write('\t\t\t<trkpt lat="' + str(lat) + '" lon="' + str(lon) + '"> </trkpt>\n')

                            f.write('\t\t</trkseg>\n')
                    f.write('\t</trk>\n')
f.write('</gpx>\n')
f.close()

Download missing parent elements for the selected element:

#!/bin/jython
'''

This code is released under the GNU General
Public License v2 or later.

The GPL v3 is accessible here:
http://www.gnu.org/licenses/gpl.html

The GPL v2 is accessible here:
http://www.gnu.org/licenses/old-licenses/gpl-2.0.html

It comes with no warranty whatsoever.

This code illustrates how to use Jython to:
* Download all referrer for an element

'''
from javax.swing import JOptionPane
from org.openstreetmap.josm import Main
import org.openstreetmap.josm.data.osm.Node as Node
import org.openstreetmap.josm.data.osm.Way as Way
import org.openstreetmap.josm.data.osm.Relation as Relation
import org.openstreetmap.josm.data.osm.TagCollection as TagCollection
import org.openstreetmap.josm.data.osm.DataSet as DataSet
import org.openstreetmap.josm.data.osm.RelationMember as RelationMember
import org.openstreetmap.josm.actions.DownloadReferrersAction as DownloadReferrersAction
#import org.openstreetmap.josm.actions.downloadtasks.DownloadReferrersTask as DownloadReferrersTask;

def getMapView():
    if Main.main and Main.main.map:
        return Main.main.map.mapView
    else:
        return None

mv = getMapView()
if mv and mv.editLayer and mv.editLayer.data:
    selectedElements = mv.editLayer.data.getSelected()
    
    if not(selectedElements):
        JOptionPane.showMessageDialog(Main.parent, "Please select an element")
    else:
        DownloadReferrersAction.downloadReferrers(mv.editLayer, selectedElements)

Download missing relation members:

#!/bin/jython
'''

This code is released under the GNU General
Public License v2 or later.

The GPL v3 is accessible here:
http://www.gnu.org/licenses/gpl.html

The GPL v2 is accessible here:
http://www.gnu.org/licenses/old-licenses/gpl-2.0.html

It comes with no warranty whatsoever.

This code illustrates how to use Jython to:
* Download all missing members of a relation

'''
from javax.swing import JOptionPane
from org.openstreetmap.josm import Main
import org.openstreetmap.josm.data.osm.Node as Node
import org.openstreetmap.josm.data.osm.Way as Way
import org.openstreetmap.josm.data.osm.Relation as Relation
import org.openstreetmap.josm.data.osm.TagCollection as TagCollection
import org.openstreetmap.josm.data.osm.DataSet as DataSet
import org.openstreetmap.josm.data.osm.RelationMember as RelationMember
import org.openstreetmap.josm.gui.dialogs.relation.DownloadRelationMemberTask as DownloadRelationMemberTask

def getMapView():
    if Main.main and Main.main.map:
        return Main.main.map.mapView
    else:
        return None

mv = getMapView()
if mv and mv.editLayer and mv.editLayer.data:
    selectedRelations = mv.editLayer.data.getSelectedRelations()
    
    if not(selectedRelations):
        JOptionPane.showMessageDialog(Main.parent, "Please select a node")
    else:
        for relation in selectedRelations:
            if relation.hasIncompleteMembers():
                #print dir(relation)
                print dir(DownloadRelationMemberTask)
                DownloadRelationMemberTask.run(DownloadRelationMemberTask(relation, relation.getIncompleteMembers(), mv.editLayer ))

Validate an rcn route relation:

#!/bin/jython
'''
- Validation of a rcn route relation

This code is released under the GNU General
Public License v2 or later.

The GPL v3 is accessible here:
http://www.gnu.org/licenses/gpl.html

The GPL v2 is accessible here:
http://www.gnu.org/licenses/old-licenses/gpl-2.0.html

It comes with no warranty whatsoever.

This code illustrates how to use Jython to:
* loop over all members of a route relation
* find out whether member is node, way or relation
* add/change properties of a relation
* remove properties of a relation
* add members to a relation
* remove members from a relation
* sort all members backwards

* How to set an element selected

'''
from javax.swing import JOptionPane
from org.openstreetmap.josm import Main
import org.openstreetmap.josm.data.osm.Node as Node
import org.openstreetmap.josm.data.osm.Way as Way
import org.openstreetmap.josm.data.osm.Relation as Relation
import org.openstreetmap.josm.data.osm.TagCollection as TagCollection
import org.openstreetmap.josm.data.osm.DataSet as DataSet
import org.openstreetmap.josm.data.osm.RelationMember as RelationMember

def getMapView():
    if Main.main and Main.main.map:
        return Main.main.map.mapView
    else:
        return None

mv = getMapView()
if mv and mv.editLayer and mv.editLayer.data:
    selectedRelations = mv.editLayer.data.getSelectedRelations()

    if not(selectedRelations):
        JOptionPane.showMessageDialog(Main.parent, "Please select a route relation")
    else:
        print
        for route in selectedRelations:
            Main.main.getCurrentDataSet().setSelected(route.getMember(0).getWay())
            name = route.get('name')
            if name and name == route.get('note'):
                print 'removing name when it is the same as note'
                route.remove('name')
            rcn_refs=[]
            memberslist = []
            continuous = True
            for member in route.getMembers():
                if member.isWay():
                    memberslist.append(member)
                    way = member.getWay()
                    #JOptionPane.showMessageDialog(Main.parent, 'way is selected')
                    endnodes = [way.getNode(0), way.getNode(way.nodesCount-1)]
                    for endnode in endnodes:
                        rcn_ref = endnode.get('rcn_ref')
                        if rcn_ref:
                            rcn_refs.append(int(rcn_ref))
            print rcn_refs
            if len(rcn_refs) > 1:
                if rcn_refs[0] > rcn_refs[1]:
                    rcn_refs.sort()
                    print 'flipping members order'
                    for member in reversed(memberslist):
                        route.addMember( route.getMembersCount(), member)
                        route.removeMember (0)
                route.put('note', str(rcn_refs[0]).zfill(2) + '-' + str(rcn_refs[1]).zfill(2))
            else:
                print 'less than 2 end nodes with rcn_ref found'