BlackBerry Developer's Blog

[#1]

In yesterday's BlackBerry API Hidden Gems post, I showed you some of my favorite classes and methods oft overlooked within BlackBerry® APIs. I've got a few more in store for you today, so let's get started!

IntVector 

In the net.rim.device.api.util package there are a bunch of collections for storing primitive Java types, such as ‘int’, ‘byte’, and ‘long’, which mirror the equivalent java.util classes.  Using these classes to store the primitive types is more efficient in both memory and time than storing wrapper objects in standard java.util collections.

My favourite example is IntVector.  IntVector has the same methods as java.util.Vector but stores primitive ‘int’ values instead of Object references.  Under the hood it uses an int[] array to store values instead of an Object[] array and therefore no conversions between ‘int’ and Integer are necessary.   This makes IntVector much better for storing ‘int’ values than java.util.Vector as it is both faster and uses less memory.  It is also fully synchronized, just like java.util.Vector.

Other adapted classes in net.rim.device.api.util include:

• ByteVector and LongVector: similar to IntVector but for ‘byte’ and ‘long’ types.
• IntHashtable, LongHashtable: adaptations of Hashtable that use primitive ‘int’ and ‘long’ values as the keys, and Objects as the values.
• ToIntHashtable, ToLongHashtable: similar to IntHashtable and LongHashtable but uses Objects for the keys and ‘int’ and ‘long’ for the values.

Here is an example usage of IntVector to store a list of high scores, with the highest scores at the lowest indices.

public class HighScores {

    private IntVector _scores;

    public HighScores() {
        _scores = new IntVector();
    }

    public void add(int score) {
        if (_scores.contains(score)) {
            return; // already there
        }

        boolean isAdded = false;
        for (int i = 0; i < _scores.size(); i++) {
            if (_scores.elementAt(i) < score) {
                _scores.insertElementAt(score, i);
                isAdded = true;
                break;
            }
        }

        if (!isAdded) {
            _scores.addElement(score);
        }

        while (_scores.size() > 10) {
            _scores.removeElementAt(_scores.size() - 1);
        }
    }

    public int getHighScore() {
        if (_scores.isEmpty()) {
            return 0;
        } else {
            return _scores.elementAt(0);
        }
    }

    public int[] getHighScores() {
        int[] array = new int[_scores.size()];
        _scores.copyInto(array);
        return array;
    }
}

Timer and TimerTask 

Like weak references, this next gem is also defined in CLDC but is mostly overlooked for its utility.  Suppose you want to perform background tasks in your application.  You can either use Application.invokeLater() or devise a grandiose background thread implementation that cleverly uses Java® synchronization primitives to efficiently perform background event dispatching.  The former consumes your application’s event thread, potentially causing UI lag, and the latter is just a lot of work.

I recommend whipping out Timer and TimerTask for background task processing.  Each Timer object has exactly one background thread which processes TimerTasks sequentially.  These tasks can be scheduled to occur immediately, after some delay, at a particular time, or repeatedly at a given interval.

The sample below shows how to use Timer and TimerTask to notify an object on a non-event thread about the user pressing the trackball.

 

public class MyScreen extends net.rim.device.api.ui.container.MainScreen {

    private Timer _timer;

    public MyScreen() {
        this.setTitle("Timer Demo");
        this._timer = new Timer();
    }

    public void onTrackballClick() {
        System.out.println("Quit pressing the trackball!");
    }

    protected boolean navigationClick(int status, int time) {
        this._timer.schedule(new ClickTask(), 0);
        return super.navigationClick(status, time);
    }

    private class ClickTask extends TimerTask {
        public void run() {
            onTrackballClick();
        }
    }
}

There are many more hidden gems in the BlackBerry® SDK but just not enough time here to share them all.  I will be doing a talk on this topic at the 2009 BlackBerry Developer Conference and plan to talk about some hidden gems not mentioned here as well as some lesser-known cool features of the JDE itself.  If you have found any hidden gems of your own please comment on this post to share your great discovery with the world!  I’d love to know which APIs you find useful.

[#2]

I just found the TimerTask a few weeks ago, and it has been a big help within my application.  I would like to know understand the threading model better. I did not take any Java or OOP when I was in school it was all patch programming.  Any threading information would be very helpful also.

Another request I would like to make would be how to make the UI fields look nicer then the default.  I know you have to override the paint method, but are there any other hidden UI gems that could be shared?

Thanks, 

Justin

[#3]

Hi Justin,

The thread model on BlackBerry is more-or-less the same as Java code running on a desktop PC.  It is defined by the JVM and CLDC specifications and therefore follows the standard Java thread model.  You can launch a thread by creating an instance of java.lang.Thread and invoking its start() method.  Each BlackBerry application is limited in the number of threads it can have running at any given time, and if you hit that upper limit then start() will throw java.lang.OutOfMemoryError... but I've never reached the limit before!  Is there anything in particular you'd like to know about the BlackBerry threading model?

As for the UI, you are right that overriding paint() is one way to customize the look-and-feel of the user interface components, but it is very "low-level".  I don't often work with UI code so I don't know of many hidden gems there.  But for not-so-hidden features... In JDE 4.6.0 the package net.rim.device.api.ui.decor was added to allow an easy way to set the background and border of a field.  And in JDE 5.0.0 there have been a few improvements too.  The class net.rim.device.api.ui.FontManager was added and the existing Font API augmented to allow much more rich control over the text displayed on a UI.  Also, net.rim.device.api.ui.TransitionContext was added to provide nifty screen transistion (fade, slide, wipe, zoom).  I'm sure there are more changes coming down the pipe too!

Thanks for your comments.  I'll look into some UI hidden gems to incorporate into my presentation at DevCon.  I'm sure they're out there, just waiting to be found!  Anyone know of any?

--Denver

[#4]

How i do to sort a vector easy like vector.sort();

[#5]

There are a couple of different solutions to sorting a Vector.

Solution 1: Copy into an Array

The first and most obvious solution is to copy the Vector's contents into an array, invoke Arrays.sort() on the array, and then copy the array back into the Vector.  Of course, this is somewhat wasteful because you have to create a temporary array and copy the elements in to and out of the array.  Here is one way to implement this method:

public static void sort(Vector vector, Comparator comparator) {
    synchronized (vector) {
        Object[] array = new Object[vector.size()];
        vector.copyInto(array);
        net.rim.device.api.util.Arrays.sort(array, comparator);
        for (int i = 0; i < array.length; i++) {
            vector.setElementAt(array[i], i);
        }
    }
}
 

Solution 2: Vector Subclass

To avoid the waste created in solution 1, you can instead create a subclass of Vector, which gives you access to the protected variable "elementData", and sort the elements in-place.  When using this solution, make sure to declare the sorting method "synchronized" in order for your Vector implementation to remain thread safe.  Here is a simple implementation of this solution:

public class MySortableVector extends Vector {
    public synchronized void sort(Comparator comparator) {
        net.rim.device.api.util.Arrays.sort(this.elementData, 0,
            this.elementCount, comparator);
    }
}

Solution 3: SimpleSortingVector

There is a RIM custom class that provides the functionality to sort a Vector: net.rim.device.api.util.SimpleSortingVector.  It is basically an implementation of solution 2 and provides the option to either sort the elements of the Vector as they are added or perform a sort on the Vector on demand.  There is also a class SimpleSortingIntVector which is the same as IntVector but sorts its elements like SimpleSortingVector.

Hope this helps.

--Denver

Message Edited by dconeybeare on 08-17-2009 10:13 AM

[#6]

Hi Denver

Great articles! I use Timers everywhere for background thread stuff, and it works great. I also use it for an GUI animation framework that I've created for all my ScreamingToaster apps for BlackBerry. 

Here's another class I find very useful - StringUtilities.stringToKeywords();. I use this all the time in custom lists that I create.

Another class that I've have to create myself is ArrayList. It's like Vector, but not synchronized. It's much more lightweight than using Vector, but much easier to use than direct array manipulation. I can share the code with this blog if there's an easy way to do so.

Thanks

Nazmul.