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 referrers for an element

'''
from javax.swing import JOptionPane
from org.openstreetmap.josm import Main
import org.openstreetmap.josm.actions.DownloadReferrersAction as DownloadReferrersAction

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

editLayer = Main.getLayerManager().getEditLayer()
if editLayer:
    selectedRelations = editLayer.data.getSelectedRelations()
    
    if not(selectedRelations):
        JOptionPane.showMessageDialog(Main.parent, "Please select a relation")
    else:
        for relation in selectedRelations:
            if relation.hasIncompleteMembers():
                #print dir(relation)
                print dir(DownloadRelationMemberTask)
                DownloadRelationMemberTask.run(DownloadRelationMemberTask(relation, relation.getIncompleteMembers(), 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 the member is a node, a way or a 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.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.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 re

commandsList = []
reNumberDashNumber = re.compile(r'\d+-\d+')
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:
    dummy_relation = Relation()
    selectedRelations = mv.editLayer.data.getSelectedRelations()

    if not(selectedRelations):
        JOptionPane.showMessageDialog(Main.parent, "Please select a route relation")
    else:
        print
        for route in selectedRelations:
            newRelation = Relation(route)
            relationChanged = False
            name = route.get('name')
            if name:
                if reNumberDashNumber.match(name):
                    print 'removing name when it is of the form ##-##'
                    newRelation.remove('name')
                    relationChanged = True
            else:
                name = ''
            ref = route.get('ref')
            if ref:
                if reNumberDashNumber.match(ref):
                    print 'removing ref when it is of the form ##-##'
                    newRelation.remove('ref')
                    relationChanged = True
            else:
                ref = ''
            if relationChanged:
                commandsList.append(Command.ChangeCommand(route, newRelation))
                
                Main.main.undoRedo.add(Command.SequenceCommand("Removing name and/or ref " + name + '/' + ref, commandsList))
                commandsList = []

            rcn_refs = []; route_relation_names = []; memberslist = []
            endnodes = []; prev_endnodes = []
            continuous_forward = True; continuous_backward = True
            prev_role = None; prev_endnodes_before_forward = None; last_endnodes_before_backward = None
            for member in route.getMembers():
                if member.isWay():
                    role = member.getRole()
                    memberslist.append(member)
                    way = member.getWay()
                    #JOptionPane.showMessageDialog(Main.parent, 'way is selected')
                    endnodes = [way.getNode(0), way.getNode(way.nodesCount-1)]
                    notfoundyet = True
                    for endnode in endnodes:
                        # inventorizing of rcn_ref on end nodes
                        rcn_ref = endnode.get('rcn_ref')
                        if rcn_ref:
                            rcn_refs.append(int(rcn_ref))
                            for referrer in endnode.getReferrers():
                                if referrer.getType() is dummy_relation.getType():
                                    if referrer.get('type')=='network' and referrer.get('network')=='rcn':
                                        relname=referrer.get('name')
                                        if relname:
                                            route_relation_names.append(relname)
                                        
                                    elif referrer.get('type')=='collection':
                                        route_relation_names.append('Node not assigned to network yet')
                        # checking for continuity on ways
                        if notfoundyet:
                            if role:
                                if prev_role:
                                    if role=='forward' and prev_role=='forward' and endnode in prev_endnodes:
                                        notfoundyet = False
                                    elif role=='forward' and prev_role=='backward' and endnode in last_endnodes_before_backward:
                                        notfoundyet = False
                                    elif role=='backward' and prev_role=='forward' and endnode in prev_endnodes:
                                        notfoundyet = False
                                    elif role=='backward' and prev_role=='backward' and endnode in prev_endnodes:
                                        notfoundyet = False
                                else:
                                    if role=='forward' and endnode in prev_endnodes:
                                        notfoundyet = False
                                    elif role=='backward' and endnode in prev_endnodes:
                                        notfoundyet = False
                            else:
                                if prev_role:
                                    if prev_role=='forward' and endnode in prev_endnodes:
                                        notfoundyet = False
                                    elif prev_role=='backward' and endnode in last_endnodes_before_backward:
                                        notfoundyet = False
                                else:
                                    if endnode in prev_endnodes:
                                        notfoundyet = False
                    # Analysis of continuity of ways
                    if prev_endnodes and notfoundyet:
                        if role:
                            if role == 'forward':
                                continuous_forward = False
                            elif role == 'backward':
                                continuous_backward = False
                        else:
                            continuous_forward = False
                            continuous_backward = False
                    if role=='forward':
                        if not(prev_endnodes_before_forward):
                            prev_endnodes_before_forward  = prev_endnodes
                    elif prev_role=='forward' and role=='backward':
                        if not(last_endnodes_before_backward):
                            last_endnodes_before_backward = prev_endnodes
                    elif not(role) and prev_role=='backward':
                        prev_endnodes_before_forward = None
                    prev_role = role
                    prev_endnodes = endnodes
            # Drawing conclusions about continuity of ways
            if continuous_forward:
                print 'route is continous in the forward direction'
            else:
                print 'route is NOT CONTINUOUS in the forward direction'
            if continuous_backward:
                print 'route is continous in the backward direction'
            else:
                print 'route is NOT CONTINUOUS in the backward direction'

            # Drawing conclusions about rcn_refs
            print rcn_refs
            if len(rcn_refs) > 1:
                newRelation = Relation(route)
                relationChanged = False

                if rcn_refs[0] > rcn_refs[1]:
                    rcn_refs.sort()
                    print 'Flipping members order'
                    for member in reversed(memberslist):
                        newRelation.addMember( newRelation.getMembersCount(), member)
                        newRelation.removeMember (0)
                    commandsList.append(Command.ChangeCommand(route, newRelation))
                    Main.main.undoRedo.add(Command.SequenceCommand("Flipping order of members", commandsList))
                    commandsList = []
                note = route.get('note')
                newNote = str(rcn_refs[0]).zfill(2) + '-' + str(rcn_refs[1]).zfill(2)
                if not(note) or note != newNote:
                    if not(note): note = 'nothing'
                    newRelation.put('note', newNote)
                    relationChanged = True
                    commandsList.append(Command.ChangeCommand(route, newRelation))
                
                    Main.main.undoRedo.add(Command.SequenceCommand("Changing note from " + note + ' to ' + newNote, commandsList))
                    commandsList = []

                if len(route_relation_names) > 1 and route_relation_names[0] != route_relation_names[1]:
                    print
                    print 'This is probably a CONNECTION to another network'
                    print route_relation_names
            else:
                print 'less than 2 end nodes with rcn_ref found'

Python/RCN_Route_Validator

Remove extra ways resulting from Potlatch way split operations under turn restriction relations

#!/bin/jython

'''
RepairTurns.py  - Remove extra ways resulting from Potlatch way split operations under turn restriction relations

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 Loops through selected turn restriction relations, trying to remove ways split from originally the same way (with to / from roles) under turn restriction relations which should no longer remain as members of these relations, as a result of a Potlatch issue: https://trac.openstreetmap.org/ticket/3254

Only work for turn restrictions with one via node

e.g. Original      : from: Way1, via: Node, to:Way2
     Split         : from: Way1a, from: Way1b, via: Node, to: Way2
     After running : from: Way1b, via: Node, to: Way2

This code illustrates how to use Jython to:
* process selected items
* download missing primitives in the same thread (blocking)
* process, validate and remove members from relations

'''
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
import org.openstreetmap.josm.io.MultiFetchServerObjectReader as MultiFetchServerObjectReader
import org.openstreetmap.josm.gui.progress.PleaseWaitProgressMonitor as PleaseWaitProgressMonitor
import org.openstreetmap.josm.command as Command

class RestrictionError(Exception):
    pass

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

def getMembers (restriction):
    memberlist = dict()
    for member in restriction.getMembers():
        memberRole = member.getRole()
        if memberRole == "via":
            if member.isNode() and not "via" in memberlist:
                memberlist[memberRole] = [member]
            else:
                raise RestrictionError, "More than one via role or via not a node"
        elif memberRole in ("from", "to"):
            if member.isWay():
                try:
                    memberlist[memberRole].append (member)
                except KeyError:
                    memberlist[memberRole] = [member]
            else:
                raise RestrictionError, "From or to role not a way"
        else: 
            raise RestrictionError, "Unknown role " + memberRole

    if len(memberlist.keys())<3:
        raise RestrictionError, "Some roles missing: Only " + ",".join (memberlist.keys()) + " found"
    return memberlist

def downloadPrimitives (primitives, editlayer):
    """
        Download a list of primitives from server, and merge into editlayer. Blocking.
    """
    monitor = PleaseWaitProgressMonitor()
    monitor.showForegroundDialog()   

    print "Downloading"
    try:
        objectReader = MultiFetchServerObjectReader().append (primitives)
        dataSet = objectReader.parseOsm (monitor)
        editlayer.mergeFrom (dataSet)
        editlayer.onPostDownloadFromServer()
        if (not objectReader.getMissingPrimitives().isEmpty()) :
            raise RestrictionError, "Unable to download missing primitives"
        print "Download completed"    
    finally:
        monitor.close()

def checkIfConnected (node, way, reverse):
    """
        Return (connected, next node to compare (i.e. other end of the node) if true)
    """
    if (way.isOneway() != 0 and reverse):
        return node == way.lastNode(True), way.firstNode(True) # True: auto process case whan isOneway == -1
    if (way.isOneway() != 0):     # not reverse
        return node == way.firstNode(True), way.lastNode(True)
    if node == way.firstNode():
        return True, way.lastNode()
    if node == way.lastNode():
        return True, way.firstNode()
    return False, node   


def repairrestriction (relation, memberlist, editLayer):
    """
        Download missing members if needed, get list of members to remove, and remove them if no error raised during checking
    """
    incompleteMembers = relation.getIncompleteMembers()
    if incompleteMembers:
          downloadPrimitives (incompleteMembers, editLayer);        

    fromRemovalList = []; toRemovalList = []
    
    if len (memberlist["from"]) >= 1:
        currnode = memberlist["via"][0].getNode()
        firstMember = True
        failed = False;
        # trace "from" members to confirm if split from one way
        for member in reversed(memberlist['from']):
            connected, currnode = checkIfConnected (currnode, member.getWay(), True)
            if not connected:
                if not firstMember:
                    raise RestrictionError, "from ways not continuous from via node" 
                failed = True
                break
            if not firstMember:
                fromRemovalList.append (member)
            else:
                firstMember = False

        if failed: # Second attempt in case sequence reversed when split
            currnode = memberlist["via"][0].getNode()
            for member in memberlist['from']:
                connected, currnode = checkIfConnected (currnode, member.getWay(), True)
                if not connected:
                    raise RestrictionError, "from ways not continuous from via node"
                if not firstMember:
                    fromRemovalList.append (member)
                else:
                    firstMember = False
                                                                        
    if len (memberlist["to"]) >= 1:
        currnode = memberlist["via"][0].getNode()
        firstMember = True
        failed = False
        # trace "to" members to confirm if split from one way
        for member in memberlist['to']:
            connected, currnode = checkIfConnected (currnode, member.getWay(), False)
            if not connected:
                if not firstMember:
                    raise RestrictionError, "to ways not continuous from via node" 
                failed = True
                break
            if not firstMember:
                toRemovalList.append (member)
            else:
                firstMember = False

        if failed: # Second attempt in case sequence reversed when split
            currnode = memberlist["via"][0].getNode()
            for member in reversed(memberlist['to']):
                connected, currnode = checkIfConnected (currnode, member.getWay(), False)
                if not connected:
                    raise RestrictionError, "to ways not continuous from via node"
                if not firstMember:
                    toRemovalList.append (member)
                else:
                    firstMember = False          
                         
    # to remove ways in fromRemovalList, toRemovalList          
    newRelation = Relation(relation)
    waysToRemove = set()
    for removalList in [fromRemovalList, toRemovalList]:
        waysToRemove |= set ([m.getWay() for m in removalList])
    newRelation.removeMembersFor (waysToRemove)
    print "Remove way(s) id:" + ",".join ([str(w.getId()) for w in waysToRemove])
    return Command.ChangeCommand (relation, newRelation)   
    
    
validrestrictiontypes = ('only_straight_on', 'only_right_turn', 'only_left_turn', 'no_right_turn', 'no_left_turn', 'no_straight_on', 'no_u_turn')
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 one or more relations")
    else:
        commandsList = []
        for relation in selectedRelations:
            if relation.get('type') == "restriction" and relation.get('restriction') in validrestrictiontypes:
                try:
                    memberlist = getMembers (relation)      
                    #print "".join(v * len(memberlist[v]) for v in memberlist.keys())           
                    if (len (memberlist["from"])) > 1 or (len (memberlist["to"])) > 1 :
                        # Repair attempt
                        print "Attempt repair",
                        print "relation id: " + str(relation.getId())
                        command = repairrestriction (relation, memberlist, mv.editLayer)
                        print "Success"                         
                        commandsList.append (command)
                except RestrictionError, e:
                    print str(e), "; relation id: "+ str(relation.getId())
                
        
        Main.main.undoRedo.add(Command.SequenceCommand("Repair turn restrictions", commandsList))
        commandsList=[]