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Java Enums in C#?

February 14, 2014 / Jan Rabe / 0 Comments

I really love C#! Almost all features like delegates, extensions methods, constraints, lambdas, refs, “magic methods”, etc. are really super convinient to use. It’s totally my favorite language so far and trust me I’ve been around with C/C++, Php, Javascript, Java. I pretty much code all the time in C# nowedays.

Probably one feature that Java did way better than C# is the way to extend enums. As stated on this website especially made for java to c# converting people.

Enums are used to create and group together a list of user defined named constants. Although on the surface the enumerated types in C# and Java seem quite similar there are some significant differences in the implementation of enumerated types in both languages. In Java, enumerated types are a full fledged class which means they are typesafe and can be extended by adding methods, fields or even implementing interfaces. Whereas in C#, an enumerated type is simply syntactic sugar around an integral type (typically an int) meaning they cannot be extended and are not typesafe.

You can use enums in Java as collection of concrecte behaviour implementations:

public interface IStringFilterCommand {

  public boolean filter(@NotNull final String source, @NotNull final String searchString);
}

public enum StringFilterCommand implements IStringFilterCommand {

  IS() {
    @Override
    public boolean filter(@NotNull final String source, @NotNull final String searchString) {
      return source.matches(searchString);
    }
  },
  CONTAINS() {
    @Override
    public boolean filter(@NotNull final String source, @NotNull final String searchString) {
      return source.contains(searchString);
    }
  },
  CONTAINS_NOT() {
    @Override
    public boolean filter(@NotNull final String source, @NotNull final String searchString) {
      return !source.contains(searchString);
    }
  },
  STARTS_WITH() {
    @Override
    public boolean filter(@NotNull final String source, @NotNull final String searchString) {
      return source.startsWith(searchString);
    }
  },
  ENDS_WITH() {
    @Override
    public boolean filter(@NotNull final String source, @NotNull final String searchString) {
      return source.endsWith(searchString);
    }
  };
}

IStringFilterCommand filter= getFilterFromSomewhere();
filter.filter("blakeks", "bla");

or directly

StringFilterCommand .STARTS_WITH.filter("blakeks", "bla");

or with static import:

STARTS_WITH.filter("blakeks", "bla");

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public interface IStringFilterCommand {

public boolean filter(@NotNull final String source, @NotNull final String searchString);

}

public enum StringFilterCommand implements IStringFilterCommand {

IS() {

@Override

public boolean filter(@NotNull final String source, @NotNull final String searchString) {

return source.matches(searchString);

}

},

CONTAINS() {

@Override

public boolean filter(@NotNull final String source, @NotNull final String searchString) {

return source.contains(searchString);

}

},

CONTAINS_NOT() {

@Override

public boolean filter(@NotNull final String source, @NotNull final String searchString) {

return !source.contains(searchString);

}

},

STARTS_WITH() {

@Override

public boolean filter(@NotNull final String source, @NotNull final String searchString) {

return source.startsWith(searchString);

}

},

ENDS_WITH() {

@Override

public boolean filter(@NotNull final String source, @NotNull final String searchString) {

return source.endsWith(searchString);

}

};

}

IStringFilterCommand filter= getFilterFromSomewhere();

filter.filter("blakeks", "bla");

or directly

StringFilterCommand .STARTS_WITH.filter("blakeks", "bla");

or with static import:

STARTS_WITH.filter("blakeks", "bla");

Or have a concrecte amount of certain Objects of a kind like a represenation of different resolutions.

java enum

Sure you can do it with normal classes, readonly attributes in c# too. But i was wondering how much of the functionality you could “port” towards c# with the help of generics, extension methods and injected attributes. So this is a small test i came up with the help of some respective stackoverflow articles.

c# javaenum test

1	c# javaenum test

Conclusion

Well it’s far from elegant/readable or even practically usable. However it’s possible to a certain extend. Feel free to correct me.

Android: OpenGL 1.0 and 2.0 infos

January 9, 2014 / Jan Rabe / 1 Comment

So here I was again, trying to figure out a way to get opengl infos like max texture size, max uniform vectors, max vertex attributes, etc. for several android devices. Technically you could just use a small getter:

Log.v("GL_MAX_TEXTURE_UNITS:", glGetIntegerv(GLES10.GL_MAX_TEXTURE_UNITS));

public static int glGetIntegerv(int value) {
  size = IntBuffer.allocate(1);
  GLES10.glGetIntegerv(value, size);
  return size.get(0);
}

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Log.v("GL_MAX_TEXTURE_UNITS:", glGetIntegerv(GLES10.GL_MAX_TEXTURE_UNITS));

public static int glGetIntegerv(int value) {

size = IntBuffer.allocate(1);

GLES10.glGetIntegerv(value, size);

return size.get(0);

}

The problem was that on many devices the the returned number would always be 0. That’s because there hasn’t been created an opengl context yet. As suggested on Stackoverflow you could create a GLSurfaceView, add a renderer which could read the required infos by adding the glsurfaceview to the actual main active view and simply remove itself when done. In order to get opengles 1.0 and opengles 2.0 infos you would need to create two surfacesviews with different opengl versions. The following example looks a bit complicated, because I use fragments which i need to update on the main thread after I got all the infos I wanted. A full example is on github.

How to get the MAC address on Android

May 24, 2013 / Jan Rabe / 2 Comments

(A test project can be found on github)

Since you can easily get confused with the many permissions provided by google, let me show you two ways to get the mac address on android. The first approach would be to use the WifiManager.getMacAdress().

/**
 * Returns MAC Address.
 * 
 * Note: requires  in AndroidManifest.xml
 * (credits: http://stackoverflow.com/a/15203979)
 *
 * @return MAC Address.
 */
public static String getMACAddress(@NotNull Activity activity) {
	return ((WifiManager) activity.getSystemService(Context.WIFI_SERVICE)).getConnectionInfo().getMacAddress();
}

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/**

* Returns MAC Address.

*

* Note: requires in AndroidManifest.xml

* (credits: http://stackoverflow.com/a/15203979)

*

* @return MAC Address.

*/

public static String getMACAddress(@NotNull Activity activity) {

return ((WifiManager) activity.getSystemService(Context.WIFI_SERVICE)).getConnectionInfo().getMacAddress();

}

However there are Disadvantages:

Device should have Wi-Fi (where not all devices have Wi-Fi)
If Wi-Fi present in device should be turned on otherwise does not report the MAC address
And the suspicious permission ACCESS_WIFI_STATE

Another approach is the use the NetworkInterface.getHardwareAddress()

/**
 * Returns MAC address of the given interface name.
 * 
 * credits to http://stackoverflow.com/questions/6064510/how-to-get-ip-address-of-the-device/13007325#13007325
 * 
 * Note: requires   and 
 *                  in AndroidManifest.xml
 * 
 * @param interfaceName eth0, wlan0 or NULL=use first interface 
 * @return  mac address or empty string
 */
  @TargetApi(Build.VERSION_CODES.GINGERBREAD)
 public static String getMACAddress(@NotNull final String interfaceName) {
     String macaddress = "";
     try {
         final List&lt;NetworkInterface&gt; interfaces = Collections.list(NetworkInterface.getNetworkInterfaces());
         for (final NetworkInterface intf : interfaces) {
             if (interfaceName != null) {
                 if (!intf.getName().equalsIgnoreCase(interfaceName)) continue;
             }
             final byte[] mac = intf.getHardwareAddress();
             if (mac==null) continue;
             final StringBuilder buf = new StringBuilder();
             for (int idx=0; idx &lt;= mac.length; idx++)
                 buf.append(String.format("%02X:", mac[idx]));
             if (buf.length()&gt;=0) buf.deleteCharAt(buf.length()-1);
                 macaddress = buf.toString();
             if(!macaddress.equals("")) break;
         }
     } catch (final Exception ex) { } // for now eat exceptions
     return macaddress ;
 }

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/**

* Returns MAC address of the given interface name.

*

* credits to http://stackoverflow.com/questions/6064510/how-to-get-ip-address-of-the-device/13007325#13007325

*

* Note: requires and

* in AndroidManifest.xml

*

* @param interfaceName eth0, wlan0 or NULL=use first interface

* @return mac address or empty string

*/

@TargetApi(Build.VERSION_CODES.GINGERBREAD)

public static String getMACAddress(@NotNull final String interfaceName) {

String macaddress = "";

try {

final List<NetworkInterface> interfaces = Collections.list(NetworkInterface.getNetworkInterfaces());

for (final NetworkInterface intf : interfaces) {

if (interfaceName != null) {

if (!intf.getName().equalsIgnoreCase(interfaceName)) continue;

}

final byte[] mac = intf.getHardwareAddress();

if (mac==null) continue;

final StringBuilder buf = new StringBuilder();

for (int idx=0; idx <= mac.length; idx++)

buf.append(String.format("%02X:", mac[idx]));

if (buf.length()>=0) buf.deleteCharAt(buf.length()-1);

macaddress = buf.toString();

if(!macaddress.equals("")) break;

}

} catch (final Exception ex) { } // for now eat exceptions

return macaddress ;

}

Disadvantage: uses permissions too, although they are required for your app to access the internet anyway and more likely commonly known to the end-user.

Conclusion:

Carring about permissions can be a pain in the butt there are even other ways if you just want identifying app installations, too.

Android libgdx ShaderAssetLoader & StillModelLoader

May 11, 2013 / Jan Rabe / 0 Comments

I totally love how libgdx brings a lot of interfaces for your application to connect to the graphics library. For instance the asset manager is really thought through well in particular. It has some really useful methods like Assets.manager.getProgress(). Especially since you can easily write your own asset loader and be able to utilize the loading progress in your app.

1) Simply add your loader to the asset manager at some point.

AssetManager manager = new AssetManager();
manager.setLoader( StillModel.class, new StillModelAssetLoader( new InternalFileHandleResolver() ) );
manager.setLoader( ShaderProgram.class, new ShaderAssetLoader( new InternalFileHandleResolver() ) );

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AssetManager manager = new AssetManager();

manager.setLoader( StillModel.class, new StillModelAssetLoader( new InternalFileHandleResolver() ) );

manager.setLoader( ShaderProgram.class, new ShaderAssetLoader( new InternalFileHandleResolver() ) );

2) load your assets at required places, e.g. loading screen
(Note: SHADER_PHONG = “data/Graphics/Shader/Phong”; and MODEL_TEAPOT = “data/Graphics/Shader/teapot.obj”)

manager.load( SHADER_PHONG, ShaderProgram.class );
manager.load( MODEL_TEAPOT, StillModel.class );

1 2	manager.load( SHADER_PHONG, ShaderProgram.class ); manager.load( MODEL_TEAPOT, StillModel.class );

3) get your shader or model wherever you need them

ShaderProgram phong = manager.get( SHADER_PHONG, ShaderProgram.class );
StillModel teapotMesh = manager.get( MODEL_TEAPOT, StillModel.class );

1 2	ShaderProgram phong = manager.get( SHADER_PHONG, ShaderProgram.class ); StillModel teapotMesh = manager.get( MODEL_TEAPOT, StillModel.class );

4) free the resource by unloading when you’re done with them (e.g. disposing your app; changing screens)

manager.unload( SHADER_PHONG );
manager.unload( MODEL_TEAPOT);

1 2	manager.unload( SHADER_PHONG ); manager.unload( MODEL_TEAPOT);

That’s the shader asset loader for loading custom shaders in libgdx. (Note: adapt your extensions)

public class ShaderAssetLoader extends SynchronousAssetLoader&lt;ShaderProgram, AssetLoaderParameters&gt; {

    private static final String VERTEX_SHADER_EXTENSION = ".vsh";
    private static final String FRAGMENT_SHADER_EXTENSION = ".fsh";

    public ShaderAssetLoader ( final FileHandleResolver resolver ) {
        super( resolver );
    }

    @Override
    public ShaderProgram load ( final AssetManager assetManager, final String fileName, final AssetLoaderParameters parameter ) {
        final ShaderProgram shader = new ShaderProgram( resolve( fileName + VERTEX_SHADER_EXTENSION ), resolve( fileName + FRAGMENT_SHADER_EXTENSION ) );
        if ( shader.isCompiled() == false ) {
            throw new IllegalStateException( shader.getLog() );
        }
        return shader;
    }

    @Override
    public Array getDependencies ( final String fileName, final AssetLoaderParameters parameter ) {
        return null;
    }
}

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public class ShaderAssetLoader extends SynchronousAssetLoader<ShaderProgram, AssetLoaderParameters> {

private static final String VERTEX_SHADER_EXTENSION = ".vsh";

private static final String FRAGMENT_SHADER_EXTENSION = ".fsh";

public ShaderAssetLoader ( final FileHandleResolver resolver ) {

super( resolver );

}

@Override

public ShaderProgram load ( final AssetManager assetManager, final String fileName, final AssetLoaderParameters parameter ) {

final ShaderProgram shader = new ShaderProgram( resolve( fileName + VERTEX_SHADER_EXTENSION ), resolve( fileName + FRAGMENT_SHADER_EXTENSION ) );

if ( shader.isCompiled() == false ) {

throw new IllegalStateException( shader.getLog() );

}

return shader;

}

@Override

public Array getDependencies ( final String fileName, final AssetLoaderParameters parameter ) {

return null;

}

}

And here is the StillModel loader for loading 3D meshes:

public class StillModelAssetLoader extends SynchronousAssetLoader&lt;StillModel, AssetLoaderParameters&gt; {

    public StillModelAssetLoader ( FileHandleResolver resolver ) {
        super( resolver );
    }

    @Override
    public StillModel load ( AssetManager assetManager, String fileName, AssetLoaderParameters parameter ) {
        return ModelLoaderRegistry.loadStillModel( resolve( fileName ) );
    }

    @Override
    public Array getDependencies ( String fileName, AssetLoaderParameters parameter ) {
        return null;
    }
}

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public class StillModelAssetLoader extends SynchronousAssetLoader<StillModel, AssetLoaderParameters> {

public StillModelAssetLoader ( FileHandleResolver resolver ) {

super( resolver );

}

@Override

public StillModel load ( AssetManager assetManager, String fileName, AssetLoaderParameters parameter ) {

return ModelLoaderRegistry.loadStillModel( resolve( fileName ) );

}

@Override

public Array getDependencies ( String fileName, AssetLoaderParameters parameter ) {

return null;

}

}

Conclusion: assets are handled well in libgdx :D

Android: Saving Screenshots in OpenGLES

May 9, 2013 / Jan Rabe / 2 Comments

1) Get your helper methods:

public static void saveBitmap(@NotNull Bitmap screenshot, @NotNull String filePath, @NotNull String fileName) {
	OutputStream outStream = null;
	filePath = Environment.getExternalStorageDirectory().toString() + "/" + filePath;
	File dir = new File( filePath );
	dir.mkdirs();
	File output = new File( filePath, fileName );
	try {
		outStream = new FileOutputStream( output );
		screenshot.compress( Bitmap.CompressFormat.PNG, 100, outStream );
		outStream.flush();
		outStream.close();
		Logger.v( TAG, "Saving Screenshot [" + filePath + fileName + "]" );
	} catch ( FileNotFoundException e ) {
		Logger.e( TAG, "" + e.getMessage() );
	} catch ( IOException e ) {
		Logger.e( TAG, "" + e.getMessage() );
	}
}

@NotNull
public Bitmap captureScreenShot() {
	int width = Gdx.graphics.getWidth(); // use your favorite width
	int height = Gdx.graphics.getHeight(); // use your favorite height
	int screenshotSize = width * height;
	ByteBuffer bb = ByteBuffer.allocateDirect( screenshotSize * 4 );
	bb.order( ByteOrder.nativeOrder() );
	// any opengl context will do
	Gdx.graphics.getGL20().glReadPixels( 0, 0, width, height, Gdx.graphics.getGL20().GL_RGBA, Gdx.graphics.getGL20().GL_UNSIGNED_BYTE, bb );
	int pixelsBuffer[] = new int[screenshotSize];
	bb.asIntBuffer().get( pixelsBuffer );
	bb = null;
	Bitmap bitmap = Bitmap.createBitmap( width, height, Bitmap.Config.RGB_565 );
	bitmap.setPixels( pixelsBuffer, screenshotSize - width, -width, 0, 0, width, height );
	pixelsBuffer = null;

	short sBuffer[] = new short[screenshotSize];
	ShortBuffer sb = ShortBuffer.wrap( sBuffer );
	bitmap.copyPixelsToBuffer( sb );

	//Making created bitmap (from OpenGL points) compatible with Android bitmap
	for ( int i = 0; i &lt; screenshotSize; ++i ) {
		short v = sBuffer[i];
		sBuffer[i] = ( short ) ( ( ( v &amp; 0x1f ) &lt;&lt; 11 ) | ( v &amp; 0x7e0 ) | ( ( v &amp; 0xf800 ) &gt;&gt; 11 ) );
	}
	sb.rewind();
	bitmap.copyPixelsFromBuffer( sb );
	return bitmap;
}

@Override
public void captureScreenShot(@NotNull final String path, @NotNull final String fileName) {
	Bitmap screenshot = captureScreenShot();
	saveBitmap( screenshot, path, fileName );
	screenshot.recycle();
}

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public static void saveBitmap(@NotNull Bitmap screenshot, @NotNull String filePath, @NotNull String fileName) {

OutputStream outStream = null;

filePath = Environment.getExternalStorageDirectory().toString() + "/" + filePath;

File dir = new File( filePath );

dir.mkdirs();

File output = new File( filePath, fileName );

try {

outStream = new FileOutputStream( output );

screenshot.compress( Bitmap.CompressFormat.PNG, 100, outStream );

outStream.flush();

outStream.close();

Logger.v( TAG, "Saving Screenshot [" + filePath + fileName + "]" );

} catch ( FileNotFoundException e ) {

Logger.e( TAG, "" + e.getMessage() );

} catch ( IOException e ) {

Logger.e( TAG, "" + e.getMessage() );

}

}

@NotNull

public Bitmap captureScreenShot() {

int width = Gdx.graphics.getWidth(); // use your favorite width

int height = Gdx.graphics.getHeight(); // use your favorite height

int screenshotSize = width * height;

ByteBuffer bb = ByteBuffer.allocateDirect( screenshotSize * 4 );

bb.order( ByteOrder.nativeOrder() );

// any opengl context will do

Gdx.graphics.getGL20().glReadPixels( 0, 0, width, height, Gdx.graphics.getGL20().GL_RGBA, Gdx.graphics.getGL20().GL_UNSIGNED_BYTE, bb );

int pixelsBuffer[] = new int[screenshotSize];

bb.asIntBuffer().get( pixelsBuffer );

bb = null;

Bitmap bitmap = Bitmap.createBitmap( width, height, Bitmap.Config.RGB_565 );

bitmap.setPixels( pixelsBuffer, screenshotSize - width, -width, 0, 0, width, height );

pixelsBuffer = null;

short sBuffer[] = new short[screenshotSize];

ShortBuffer sb = ShortBuffer.wrap( sBuffer );

bitmap.copyPixelsToBuffer( sb );

//Making created bitmap (from OpenGL points) compatible with Android bitmap

for ( int i = 0; i < screenshotSize; ++i ) {

short v = sBuffer[i];

sBuffer[i] = ( short ) ( ( ( v & 0x1f ) << 11 ) | ( v & 0x7e0 ) | ( ( v & 0xf800 ) >> 11 ) );

}

sb.rewind();

bitmap.copyPixelsFromBuffer( sb );

return bitmap;

}

@Override

public void captureScreenShot(@NotNull final String path, @NotNull final String fileName) {

Bitmap screenshot = captureScreenShot();

saveBitmap( screenshot, path, fileName );

screenshot.recycle();

}

2) get a queue ready

protected ConcurrentLinkedQueue screenshotRequestedQueue = new ConcurrentLinkedQueue&lt;&gt;();

1	protected ConcurrentLinkedQueue screenshotRequestedQueue = new ConcurrentLinkedQueue<>();

3) add new filepath the the queue via e.g. events:

@Override
public boolean tap(float x, float y, int count, int button) {
	screenshotRequestedQueue.add( Math.random() * Integer.MAX_VALUE + ".png" );
	return false;
}

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@Override

public boolean tap(float x, float y, int count, int button) {

screenshotRequestedQueue.add( Math.random() * Integer.MAX_VALUE + ".png" );

return false;

}

4) IMPORTANT! save the screen at the end of the opengl render process. (Note: If try to capture somewhere in the middle you might end up with a black screen or any other funny effects.)

@Override
public void render(float delta) {

	...
	// render your stuff
	...

	// capture screen on request
	if ( !screenshotRequestedQueue.isEmpty() )
		captureScreenShot(SCREENSHOT_FOLDER, screenshotRequestedQueue.poll() );
}

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@Override

public void render(float delta) {

...

// render your stuff

...

// capture screen on request

if ( !screenshotRequestedQueue.isEmpty() )

captureScreenShot(SCREENSHOT_FOLDER, screenshotRequestedQueue.poll() );

}

How to swap two variables without a temp variable

January 14, 2013 / Jan Rabe / 0 Comments

In C

void swap(int &x, int &y)
{
    x ^= y ^= x ^= y;
}

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void swap(int &x, int &y)

{

x ^= y ^= x ^= y;

}

In Java

public void swap(int [] a) {
    assert a.length == 2;
    a[0] ^= a[1] ^= a[0] ^= a[1];
}

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public void swap(int [] a) {

assert a.length == 2;

a[0] ^= a[1] ^= a[0] ^= a[1];

}

In Assembler

__asm {
mov eax,a
mov ebx,b
mov b,eax
mov a,ebx
}

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__asm {

mov eax,a

mov ebx,b

mov b,eax

mov a,ebx

}

Fun fact: fastest is still with temp variable. (:

public void swap(int &a, int &b) 
{
    int c = a;
    a = b;
    b = c;
}

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public void swap(int &a, int &b)

{

int c = a;

a = b;

b = c;

}

Extra python:

a, b = b, a

1	a, b = b, a

How to iterate over a java map

January 9, 2013 / Jan Rabe / 0 Comments

Since I’ve been asked this a lot lately …

Extracted from Reference link (original Sergiy Kovalchuk): How to Iterate Over a Map in Java

There are several ways of iterating over a Map in Java. Lets go over the most common methods and review their advantages and disadvantages. Since all maps in Java implement Map interface, following techniques will work for any map implementation (HashMap, TreeMap, LinkedHashMap, Hashtable, etc.)

Method #1: Iterating over entries using For-Each loop.

This is the most common method and is preferable in most cases. Should be used if you need both map keys and values in the loop.

Map<integer, integer=""> map = new HashMap<integer, integer="">();
for (Map.Entry<integer, integer=""> entry : map.entrySet()) {
    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
}

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Map<integer, integer=""> map = new HashMap<integer, integer="">();

for (Map.Entry<integer, integer=""> entry : map.entrySet()) {

System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());

}

Note that For-Each loop was introduced in Java 5 so this method is working only in newer versions of the language. Also For-Each loop will throw NullPointerException if you try to iterate over a map that is null, so before iterating you should always check for null references.

Method #2: Iterating over keys or values using For-Each loop.

If you need only keys or values from the map, you can iterate over keySet or values instead of entrySet.

Map<integer, integer=""> map = new HashMap<integer, integer="">();

//iterating over keys only
for (Integer key : map.keySet()) {
    System.out.println("Key = " + key);
}

//iterating over values only
for (Integer value : map.values()) {
    System.out.println("Value = " + value);
}

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Map<integer, integer=""> map = new HashMap<integer, integer="">();

//iterating over keys only

for (Integer key : map.keySet()) {

System.out.println("Key = " + key);

}

//iterating over values only

for (Integer value : map.values()) {

System.out.println("Value = " + value);

}

This method gives slight performance advantage over entrySet iteration (about 10% faster) and is more clean.

Method #3: Iterating using Iterator.

Using Generics:

Map<integer, integer=""> map = new HashMap<integer, integer="">();
Iterator<map.entry<integer, integer="">> entries = map.entrySet().iterator();
while (entries.hasNext()) {
    Map.Entry<integer, integer=""> entry = entries.next();
    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
	entries.remove(); // avoids a ConcurrentModificationException
}

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Map<integer, integer=""> map = new HashMap<integer, integer="">();

Iterator<map.entry<integer, integer="">> entries = map.entrySet().iterator();

while (entries.hasNext()) {

Map.Entry<integer, integer=""> entry = entries.next();

System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());

entries.remove(); // avoids a ConcurrentModificationException

}

Without Generics:

Map map = new HashMap();
Iterator entries = map.entrySet().iterator();
while (entries.hasNext()) {
    Map.Entry entry = (Map.Entry) entries.next();
    Integer key = (Integer)entry.getKey();
    Integer value = (Integer)entry.getValue();
    System.out.println("Key = " + key + ", Value = " + value);
}

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Map map = new HashMap();

Iterator entries = map.entrySet().iterator();

while (entries.hasNext()) {

Map.Entry entry = (Map.Entry) entries.next();

Integer key = (Integer)entry.getKey();

Integer value = (Integer)entry.getValue();

System.out.println("Key = " + key + ", Value = " + value);

}

You can also use same technique to iterate over keySet or values.

This method might look redundant but it has its own advantages. First of all it is the only way to iterate over a map in older versions of Java. The other important feature is that it is the only method that allows you to remove entries from the map during iteration by calling iterator.remove(). If you try to do this during For-Each iteration you will get “unpredictable results” according to javadoc.

From performance point of view this method is equal to For-Each iteration.

Method #4: Iterating over keys and searching for values (inefficient).

Map<integer, integer=""> map = new HashMap<integer, integer="">();
for (Integer key : map.keySet()) {
    Integer value = map.get(key);
    System.out.println("Key = " + key + ", Value = " + value);
}

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Map<integer, integer=""> map = new HashMap<integer, integer="">();

for (Integer key : map.keySet()) {

Integer value = map.get(key);

System.out.println("Key = " + key + ", Value = " + value);

}

This might look like a cleaner alternative for method #1 but in practice it is pretty slow and inefficient as getting values by a key might be time consuming (this method in different Map implementations is 20%-200% slower than method #1). If you have FindBugs installed, it will detect this and warn you about inefficient iteration. This method should be avoided.
Conclusion

If you need only keys or values from the map use method #2. If you are stuck with older version of Java (less than 5) or planning to remove entries during iteration you have to use method #3. Otherwise use method #1.

How to boost android canvas performance with a buffered Image

January 7, 2013 / Jan Rabe / 2 Comments

When it comes to drawing to canvas on android one very big performance boost can be gained by using a buffered bitmap image. The idea is to draw lines to a bitmap. And then draw the bitmap to the screen.
This approach avoids unnecessarily redrawing elements that has been drawn already multiple times.

1) Create a bitmap in your view.

public View(Activity activity) {
    super(activity);
    DisplayMetrics metrics = new DisplayMetrics();
    activity.getWindowManager().getDefaultDisplay().getMetrics(metrics);
    bufferedImage = Bitmap.createBitmap(metrics.widthPixels, metrics.heightPixels, Bitmap.Config.ARGB_8888);
    .
    .
    .
}

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public View(Activity activity) {

super(activity);

DisplayMetrics metrics = new DisplayMetrics();

activity.getWindowManager().getDefaultDisplay().getMetrics(metrics);

bufferedImage = Bitmap.createBitmap(metrics.widthPixels, metrics.heightPixels, Bitmap.Config.ARGB_8888);

.

.

.

}

2) Remember all touch events.

@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
    int action = motionEvent.getAction();
    Point point = new Point(motionEvent.getX(), motionEvent.getY());
    switch (action) {
        case MotionEvent.ACTION_DOWN: // touch down
            linePathManager.startLine(point);
            break;
        case MotionEvent.ACTION_MOVE:  // touch drag
            linePathManager.addPoint(point);
            break;
        case MotionEvent.ACTION_UP: // stop touching
            linePathManager.endLine();
            break;
    }
    invalidate();
    return super.onTouchEvent(motionEvent);
}

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@Override

public boolean onTouch(View view, MotionEvent motionEvent) {

int action = motionEvent.getAction();

Point point = new Point(motionEvent.getX(), motionEvent.getY());

switch (action) {

case MotionEvent.ACTION_DOWN: // touch down

linePathManager.startLine(point);

break;

case MotionEvent.ACTION_MOVE: // touch drag

linePathManager.addPoint(point);

break;

case MotionEvent.ACTION_UP: // stop touching

linePathManager.endLine();

break;

}

invalidate();

return super.onTouchEvent(motionEvent);

}

3) Process all touch events. (Draw lines or something)

private Path path = new Path();

public void startLine(@NotNull Point point) {
    path.moveTo(point.x, point.y);
}
 
public void add(@NotNull Point p) {
    path.lineTo(p.x, p.y);
    path.moveTo(p.x, p.y);
}

public void close() {
    path.close();
}

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private Path path = new Path();

public void startLine(@NotNull Point point) {

path.moveTo(point.x, point.y);

}

public void add(@NotNull Point p) {

path.lineTo(p.x, p.y);

path.moveTo(p.x, p.y);

}

public void close() {

path.close();

}

4) Draw to buffered bitmap image.

lineManager.draw():

private Canvas canvas = new Canvas();

public void draw(Bitmap bitmap, Paint paint) {
    canvas.setBitmap(bitmap);
    canvas.drawPath(path, paint);
}

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private Canvas canvas = new Canvas();

public void draw(Bitmap bitmap, Paint paint) {

canvas.setBitmap(bitmap);

canvas.drawPath(path, paint);

}

5) And finally draw the buffered bitmap image.

@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    linePathManager.draw(bufferedImage, paint);
    canvas.drawBitmap(bufferedImage, 0, 0, paint);
}

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@Override

public void onDraw(Canvas canvas) {

super.onDraw(canvas);

linePathManager.draw(bufferedImage, paint);

canvas.drawBitmap(bufferedImage, 0, 0, paint);

}

Bonus: invalidate canvas only around finger area and only every 90 milliseconds.

@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
    int action = motionEvent.getAction();

    Point point = new Point(motionEvent.getX(), motionEvent.getY());
    switch (action) {
        case MotionEvent.ACTION_DOWN: // touch down
            linePathManager.startLine(point);
            break;
        case MotionEvent.ACTION_MOVE:  // touch drag
            linePathManager.addPoint(point);
            break;
        case MotionEvent.ACTION_UP:
            linePathManager.endLine();
            break;
    }

    // invalidate only finger area
    if (Calendar.getInstance().getTimeInMillis() - startTime > 90) {
        int rectangleSize = (int) (100 * metric.density);
        invalidate((int) (point.x - rectangleSize / 1.5), (int) (point.y - rectangleSize / 1.5), (int) point.x + rectangleSize, (int) point.y + rectangleSize);
        startTime = Calendar.getInstance().getTimeInMillis();
    }
    return true;
}

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@Override

public boolean onTouch(View view, MotionEvent motionEvent) {

int action = motionEvent.getAction();

Point point = new Point(motionEvent.getX(), motionEvent.getY());

switch (action) {

case MotionEvent.ACTION_DOWN: // touch down

linePathManager.startLine(point);

break;

case MotionEvent.ACTION_MOVE: // touch drag

linePathManager.addPoint(point);

break;

case MotionEvent.ACTION_UP:

linePathManager.endLine();

break;

}

// invalidate only finger area

if (Calendar.getInstance().getTimeInMillis() - startTime > 90) {

int rectangleSize = (int) (100 * metric.density);

invalidate((int) (point.x - rectangleSize / 1.5), (int) (point.y - rectangleSize / 1.5), (int) point.x + rectangleSize, (int) point.y + rectangleSize);

startTime = Calendar.getInstance().getTimeInMillis();

}

return true;

}

See also

Performance in 2D Canvas App / Game on Android and Traceview War Story

Doodle Drawer – Brushes

January 7, 2013 / Jan Rabe / 0 Comments

At my Doodle Drawer app, I’ve played with a couple of “brushes”. The idea is to treat the connection lines differently.

shaded

shaded

sketched

sketched

fur

fur

Basically the difference is that the line connections are drawn closer or further away from each line based on the formula of Harmony.

The ‘shaded brush’ looks like this:

@Override
    public void addConnections(Point nextPoint, int color, float strokeWidth) {
        ArrayList<Point> points = PointsList.points;
        for (int i = 0; i < points.size(); ++i) {
            Point curPoint = points.get(i);
            float b = curPoint.x - nextPoint.x;
            float a = curPoint.y - nextPoint.y;
            float distance = b * b + a * a;
            if (distance < 2000f * Config.DEVICE_DISPLAY_METRICS.density) {
                int alpha =  255-((int) (225f / 2000f * Config.DEVICE_DISPLAY_METRICS.density * distance));
                int newColor = Color.argb(alpha, Color.red(color), Color.green(color), Color.blue(color));
                LineList.connections.add(new Line(nextPoint, curPoint, newColor, strokeWidth * Config.BRUSH_PRESSURE * 0.5f));
            }
        }
    }

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@Override

public void addConnections(Point nextPoint, int color, float strokeWidth) {

ArrayList<Point> points = PointsList.points;

for (int i = 0; i < points.size(); ++i) {

Point curPoint = points.get(i);

float b = curPoint.x - nextPoint.x;

float a = curPoint.y - nextPoint.y;

float distance = b * b + a * a;

if (distance < 2000f * Config.DEVICE_DISPLAY_METRICS.density) {

int alpha = 255-((int) (225f / 2000f * Config.DEVICE_DISPLAY_METRICS.density * distance));

int newColor = Color.argb(alpha, Color.red(color), Color.green(color), Color.blue(color));

LineList.connections.add(new Line(nextPoint, curPoint, newColor, strokeWidth * Config.BRUSH_PRESSURE * 0.5f));

}

}

}

The sketched brush looks like this:

    @Override
    public void addConnections(Point nextPoint, int color, float strokeWidth) {
        ArrayList points = PointsList.points;
        for (int i = 0; i &lt; points.size(); ++i) {
            Point curPoint = points.get(i);
            float b = curPoint.x - nextPoint.x;
            float a = curPoint.y - nextPoint.y;
            float distance = b * b + a * a;
            if (distance &lt; 10000 * Config.DEVICE_DISPLAY_METRICS.density &amp;&amp; Math.random() &gt; (distance / 10000 * Config.DEVICE_DISPLAY_METRICS.density)) {
                int alpha = 255 - ((int) ((225f / 2000f * Config.DEVICE_DISPLAY_METRICS.density) * distance));
                int newColor =  Color.argb(alpha, Color.red(color), Color.green(color), Color.blue(color));
                final float c = 0.2f;
                LineList.connections.add(new Line(new Point(nextPoint.x + (b * c), nextPoint.y + (a * c)), new Point(curPoint.x - (b * c), curPoint.y - (a * c)),newColor, strokeWidth * 0.5f * Config.BRUSH_PRESSURE));
            }
        }
    }

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@Override

public void addConnections(Point nextPoint, int color, float strokeWidth) {

ArrayList points = PointsList.points;

for (int i = 0; i < points.size(); ++i) {

Point curPoint = points.get(i);

float b = curPoint.x - nextPoint.x;

float a = curPoint.y - nextPoint.y;

float distance = b * b + a * a;

if (distance < 10000 * Config.DEVICE_DISPLAY_METRICS.density && Math.random() > (distance / 10000 * Config.DEVICE_DISPLAY_METRICS.density)) {

int alpha = 255 - ((int) ((225f / 2000f * Config.DEVICE_DISPLAY_METRICS.density) * distance));

int newColor = Color.argb(alpha, Color.red(color), Color.green(color), Color.blue(color));

final float c = 0.2f;

LineList.connections.add(new Line(new Point(nextPoint.x + (b * c), nextPoint.y + (a * c)), new Point(curPoint.x - (b * c), curPoint.y - (a * c)),newColor, strokeWidth * 0.5f * Config.BRUSH_PRESSURE));

}

}

}

And the ‘fur brush’ looks like this:

    @Override
    public void addConnections(Point nextPoint, int color, float strokeWidth) {
        ArrayList points = PointsList.points;
        for (int i = 0; i &lt; points.size(); ++i) {
            Point curPoint = points.get(i);
            float b = curPoint.x - nextPoint.x;
            float a = curPoint.y - nextPoint.y;
            float distance = b * b + a * a;
            if (distance &lt; 4000f * Config.DEVICE_DISPLAY_METRICS.density &amp;&amp; Math.random() &gt; distance / 4000f * Config.DEVICE_DISPLAY_METRICS.density) {
                final float c = 0.5f;
                LineList.connections.add(new Line(new Point(nextPoint.x + (b * c), nextPoint.y + (a * c)), new Point(nextPoint.x - (b * c), nextPoint.y - (a * c)), color, strokeWidth * Config.BRUSH_PRESSURE * 0.5f));
            }
        }
    }

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@Override

public void addConnections(Point nextPoint, int color, float strokeWidth) {

ArrayList points = PointsList.points;

for (int i = 0; i < points.size(); ++i) {

Point curPoint = points.get(i);

float b = curPoint.x - nextPoint.x;

float a = curPoint.y - nextPoint.y;

float distance = b * b + a * a;

if (distance < 4000f * Config.DEVICE_DISPLAY_METRICS.density && Math.random() > distance / 4000f * Config.DEVICE_DISPLAY_METRICS.density) {

final float c = 0.5f;

LineList.connections.add(new Line(new Point(nextPoint.x + (b * c), nextPoint.y + (a * c)), new Point(nextPoint.x - (b * c), nextPoint.y - (a * c)), color, strokeWidth * Config.BRUSH_PRESSURE * 0.5f));

}

}

}

Java Tutorium: Aufgabe 11

January 5, 2013 / Jan Rabe / 0 Comments

Aufgabe 11

Download (PDF?RAW=TRUE, 28KB)

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