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  • Null-free "maps": Is a callback solution slower than tryGet()?

    - by David Moles
    In comments to "How to implement List, Set, and Map in null free design?", Steven Sudit and I got into a discussion about using a callback, with handlers for "found" and "not found" situations, vs. a tryGet() method, taking an out parameter and returning a boolean indicating whether the out parameter had been populated. Steven maintained that the callback approach was more complex and almost certain to be slower; I maintained that the complexity was no greater and the performance at worst the same. But code speaks louder than words, so I thought I'd implement both and see what I got. The original question was fairly theoretical with regard to language ("And for argument sake, let's say this language don't even have null") -- I've used Java here because that's what I've got handy. Java doesn't have out parameters, but it doesn't have first-class functions either, so style-wise, it should suck equally for both approaches. (Digression: As far as complexity goes: I like the callback design because it inherently forces the user of the API to handle both cases, whereas the tryGet() design requires callers to perform their own boilerplate conditional check, which they could forget or get wrong. But having now implemented both, I can see why the tryGet() design looks simpler, at least in the short term.) First, the callback example: class CallbackMap<K, V> { private final Map<K, V> backingMap; public CallbackMap(Map<K, V> backingMap) { this.backingMap = backingMap; } void lookup(K key, Callback<K, V> handler) { V val = backingMap.get(key); if (val == null) { handler.handleMissing(key); } else { handler.handleFound(key, val); } } } interface Callback<K, V> { void handleFound(K key, V value); void handleMissing(K key); } class CallbackExample { private final Map<String, String> map; private final List<String> found; private final List<String> missing; private Callback<String, String> handler; public CallbackExample(Map<String, String> map) { this.map = map; found = new ArrayList<String>(map.size()); missing = new ArrayList<String>(map.size()); handler = new Callback<String, String>() { public void handleFound(String key, String value) { found.add(key + ": " + value); } public void handleMissing(String key) { missing.add(key); } }; } void test() { CallbackMap<String, String> cbMap = new CallbackMap<String, String>(map); for (int i = 0, count = map.size(); i < count; i++) { String key = "key" + i; cbMap.lookup(key, handler); } System.out.println(found.size() + " found"); System.out.println(missing.size() + " missing"); } } Now, the tryGet() example -- as best I understand the pattern (and I might well be wrong): class TryGetMap<K, V> { private final Map<K, V> backingMap; public TryGetMap(Map<K, V> backingMap) { this.backingMap = backingMap; } boolean tryGet(K key, OutParameter<V> valueParam) { V val = backingMap.get(key); if (val == null) { return false; } valueParam.value = val; return true; } } class OutParameter<V> { V value; } class TryGetExample { private final Map<String, String> map; private final List<String> found; private final List<String> missing; public TryGetExample(Map<String, String> map) { this.map = map; found = new ArrayList<String>(map.size()); missing = new ArrayList<String>(map.size()); } void test() { TryGetMap<String, String> tgMap = new TryGetMap<String, String>(map); for (int i = 0, count = map.size(); i < count; i++) { String key = "key" + i; OutParameter<String> out = new OutParameter<String>(); if (tgMap.tryGet(key, out)) { found.add(key + ": " + out.value); } else { missing.add(key); } } System.out.println(found.size() + " found"); System.out.println(missing.size() + " missing"); } } And finally, the performance test code: public static void main(String[] args) { int size = 200000; Map<String, String> map = new HashMap<String, String>(); for (int i = 0; i < size; i++) { String val = (i % 5 == 0) ? null : "value" + i; map.put("key" + i, val); } long totalCallback = 0; long totalTryGet = 0; int iterations = 20; for (int i = 0; i < iterations; i++) { { TryGetExample tryGet = new TryGetExample(map); long tryGetStart = System.currentTimeMillis(); tryGet.test(); totalTryGet += (System.currentTimeMillis() - tryGetStart); } System.gc(); { CallbackExample callback = new CallbackExample(map); long callbackStart = System.currentTimeMillis(); callback.test(); totalCallback += (System.currentTimeMillis() - callbackStart); } System.gc(); } System.out.println("Avg. callback: " + (totalCallback / iterations)); System.out.println("Avg. tryGet(): " + (totalTryGet / iterations)); } On my first attempt, I got 50% worse performance for callback than for tryGet(), which really surprised me. But, on a hunch, I added some garbage collection, and the performance penalty vanished. This fits with my instinct, which is that we're basically talking about taking the same number of method calls, conditional checks, etc. and rearranging them. But then, I wrote the code, so I might well have written a suboptimal or subconsicously penalized tryGet() implementation. Thoughts?

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  • Display regular street map on Google Earth

    - by carrier
    I'm writing an application that displays data using Google Earth. In certain situations, it would be more convenient if, rather than displaying satellite images, the surface of the earth would look more like the 'regular map' on Google Maps. Is this possible?

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  • How to draw a line between points in google map in Android

    - by wafa.cs1
    Hello I already wrote a program that read locations from android GPS ; each locatin(long , lat) will be sent to remote server to save it and display it in a website map. what I'm trying to do now is to display my path in android by drawing line between the points I didn't find any sufficient answer until this moment! so how this can be done?

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  • Creating SVG map from geometry stored in MySQL

    - by Barnabe
    I have a group of geometries stored in MySQl (as polygon and as well-known text) representing counties. I can build a table of geometries and color codes after querying some county data (say GDP per capita). What is the best way to export this as an SVG map? I cannot find any reference to SVG conversion in the MySQL documentation.

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  • Coverting a vector of maps to map of maps in clojure

    - by Osman
    Hi, I've a vector of maps like this: [ {:categoryid 1, :categoryname "foo" } {:categoryid 2, :categoryname "bar" } {:categoryid 3, :categoryname "baz" } ] and would like to generate a map of maps like this for searching by categoryname { "foo" {:categoryid 1, :categoryname "foo" }, "bar" {:categoryid 2, :categoryname "bar" }, "baz" {:categoryid 3, :categoryname "baz" } } How can i achieve?

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  • google map api v3 - picture overlay

    - by user317005
    can anyone tell me how i can put different pictures to different locations, as shown on the url below: http://connectedwell.com/wp-content/uploads/2008/05/brightkite_friendmap.png brightkite used to have it, but they dont anymore ... and im not really sure i can use custom div tags and assign them to the google map api v3 ... didnt really find anything useful in the api documentation either ... just for "custom markers"

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  • Do not fire 'zoom_changed' event when calling fitBounds function on map

    - by Encore PTL
    Is there a way to prevent the zoom_change event from being triggered if it occurs due to fitBounds() ? I am having an issue where I need to do a search on the server from client when there is a zoom change to map but every time I call fitBounds() it causes zoom_change to trigger which causes the client to do another search on the server. I am only interested in zoom_change done by users and not programmatically using fitBounds.

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  • draw is being constantly called in my android map overlay

    - by Itsik
    I'm trying to draw a route onto my MapView. I've extended Overlay and implemented the draw() method. The route is displayed properly, although while debugging, I added a breakpoint on draw(), and noticed it is being called constantly. I only want it to be re-drawn if someone moves the map or zooms (the draw take into account these changes when drawing the route) What can cause this ?

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  • displaying the map highlighting the provinces and some additional info

    - by Sachindra
    I am using PHP open source and I need the map of a country highlighting all the states in different colors. Once a particular state is hovered over, some info about the state needs to appear. Please suggest me how to do this. Is it possible to do this using some basic stuff ... I mean nothing like what goes beyond my knowledge... Not sure if the tags that i have posted this query in is right...

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  • Finding user location before map loads

    - by 4thSpace
    I'm trying to find the user's location using: CLLocationCoordinate2D _location; CLLocation *userLoc = nil; if(appDelegate.clLocationManager.locationServicesEnabled){ userLoc = mapView.userLocation.location; _location = userLoc.coordinate; } The problem is that I haven't yet initialized the map so the above doesn't work. Is there a way to get the user's location without using mapkit? Or should I be using a different technique?

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  • Django @ Google App Engine - Site Map Framework

    - by dkp
    Hi Folks, has anybody managed to get Djangos site map framework to run on Google App Engine? I receive the following exception: ImproperlyConfigured at /sitemap.xml You haven't set the DATABASE_ENGINE setting yet. Request Method: GET Request URL: http://127.0.0.1:8080/sitemap.xml Exception Type: ImproperlyConfigured Exception Value: You haven't set the DATABASE_ENGINE setting yet. Exception Location: D:\Program Files\Google\google_appengine\lib\django\django\db\backends\dummy\base.py in complain, line 13

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  • Fluent NHibernate - Map 2 tables to one class

    - by Morten Schmidt
    Hi I have a table structure something like this table Employees EmployeeID EmployeeLogin EmployeeCustID table Customers CustomerID CustomerName What i would like is to map the structure above to one single class named: Class Employee EmployeeID EmployeeLogin EmployeeName How do i do that with fluent nhibernate ?

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  • List comprehension, map, and numpy.vectorize performance

    - by mcstrother
    I have a function foo(i) that takes an integer and takes a significant amount of time to execute. Will there be a significant performance difference between any of the following ways of initializing a: a = [foo(i) for i in xrange(100)] a = map(foo, range(100)) vfoo = numpy.vectorize(foo) a = vfoo(range(100)) (I don't care whether the output is a list or a numpy array.) Is there a better way?

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