Tutorial by Examples: v

SignedObject (java.security.SignedObject)

SignedObject is a class for the purpose of creating authentic runtime objects whose integrity cannot be compromised without being detected. More specifically, a SignedObject contains another Serializable object, the (to-be-)signed object and its signature. //Create a key KeyPairGenerator keyGen...

Java Language • Secure objects

Transformation vs Action

Spark uses lazy evaluation; that means it will not do any work, unless it really has to. That approach allows us to avoid unnecessary memory usage, thus making us able to work with big data. A transformation is lazy evaluated and the actual work happens, when an action occurs. Example: In [1]: li...

apache-spark • Getting started with apache-spark

Pitfall - Overloading instead of overriding

Consider the following example: public final class Person { private final String firstName; private final String lastName; public Person(String firstName, String lastName) { this.firstName = (firstName == null) ? "" : firstName; this.lastName = (lastN...

Java Language • Java Pitfalls - Language syntax

Drawing two rectangles on a

<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8" /> <title>Draw two rectangles on the canvas</title> <style> canvas{ border:1px solid gray; } </style> <script async...

HTML • Canvas

Exporting .csv files

Exporting using base R Data can be written to a CSV file using write.csv(): write.csv(mtcars, "mtcars.csv") Commonly-specified parameters include row.names = FALSE and na = "". Exporting using packages readr::write_csv is significantly faster than write.csv and does not ...

R Language • Reading and writing tabular data in plain-text files (CSV, TSV, etc.)

Draw behind existing shapes with "destination-over"

context.globalCompositeOperation = "destination-over" "destination-over" compositing places new drawing under existing drawings. context.drawImage(rainy,0,0); context.globalCompositeOperation='destination-over'; // sunny UNDER rainy context.drawImage(sunny,0,0);

html5-canvas • Compositing

Default compositing: New shapes are drawn over Existing shapes

context.globalCompositeOperation = "source-over" "source-over" compositing [default], places all new drawings over any existing drawings. context.globalCompositeOperation='source-over'; // the default context.drawImage(background,0,0); context.drawImage(parachuter,0,0); ...

html5-canvas • Compositing

Detect errors when writing a value on Android

There are many reasons a write operation may fail. A frequent one is because your security rules reject the operation, for example because you're not authenticated (by default a database can only be accessed by an authenticated user). You can see these security rule violations in the logcat output....

firebase • How do I listen for errors when accessing the database?

Adding a ViewPager

Make sure the following dependency is added to your app's build.gradle file under dependencies: compile 'com.android.support:support-core-ui:25.3.0' Then add the ViewPager to your activity layout: <android.support.v4.view.ViewPager android:id="@+id/viewpager" android:layo...

Android • ViewPager

Using Resolvers and Guards

We're using a toplevel guard in our route config to catch the current user on first page load, and a resolver to store the value of the currentUser, which is our authenticated user from the backend. A simplified version of our implementation looks as follows: Here is our top level route: export c...

Angular 2 • Routing (3.0.0+)

Create a Bluetooth LE Advertisement

This example shows how to advertise a custom payload from a Windows 10 device in the foreground. The payload uses a made up company (identified as 0xFFFE) and advertises the string Hello World in the advertisement. BluetoothLEAdvertisementPublisher publisher = new BluetoothLEAdvertisementPublisher(...

bluetooth • Get Started With Bluetooth LE on Windows

Listen for a Bluetooth LE Advertisement

General Listening This example shows how to listen for a specific advertisement. BluetoothLEAdvertisementWatcher watcher = new BluetoothLEAdvertisementWatcher(); // Use active listening if you want to receive Scan Response packets as well // this will have a greater power cost. watcher.Scanni...

bluetooth • Get Started With Bluetooth LE on Windows

Customizing the CardView

CardView provides a default elevation and corner radius so that cards have a consistent appearance across the platforms. You can customize these default values using these attributes in the xml file: card_view:cardElevation attribute add elevation in CardView. card_view:cardBackgroundColor attr...

Android • CardView

DROPPING A VIEW

-- Create and drop a view in the current database. CREATE VIEW few_rows_from_t1 AS SELECT * FROM t1 LIMIT 10; DROP VIEW few_rows_from_t1; -- Create and drop a view referencing a table in a different database. CREATE VIEW table_from_other_db AS SELECT x FROM db1.foo WHERE x IS NOT NULL; DROP V...

MySQL • VIEW

implement View.OnLayoutChangeListener in Nativescript

let playerLayoutChangeListener = new android.view.View.OnLayoutChangeListener( { onLayoutChange : function ( v:View, left:number, top:number, right:number, bottom:number, oldLeft:number, oldTop:number, oldRight:number, oldBottom:number):any { if (left != oldLeft || top != oldTop ...

nativescript • implement Interface

Overloading Def

You can overload a def if the signature is different: def printValue(x: Int) { println(s"My value is an integer equal to $x") } def printValue(x: String) { println(s"My value is a string equal to '$x'") } printValue(1) // prints "My value is an integer equal ...

Scala Language • Var, Val, and Def

Avoid leaking Activities with Listeners

If you implement or create a listener in an Activity, always pay attention to the lifecycle of the object that has the listener registered. Consider an application where we have several different activities/fragments interested in when a user is logged in or out. One way of doing this would be to h...

Android • Memory Leaks

Pitfall - Extending 'java.lang.Thread'

The javadoc for the Thread class shows two ways to define and use a thread: Using a custom thread class: class PrimeThread extends Thread { long minPrime; PrimeThread(long minPrime) { this.minPrime = minPrime; } public void run() { // compute primes l...

Java Language • Java Pitfalls - Threads and Concurrency

Invert or Negate image with "difference"

Render a white rectangle over an image with the composite operation ctx.globalCompositeOperation = 'difference'; The amount of the effect can be controled with the alpha setting // Render the image ctx.globalCompositeOperation='source-atop'; ctx.drawImage(image, 0, 0); // set the composite...

html5-canvas • Compositing

Filter Logoutput by level (log4j 1.x)

You can use a filter to log only messages "lower" than e.g. ERROR level. But the filter is not supported by PropertyConfigurator. So you must change to XML config to use it. See log4j-Wiki about filters. Example "specific level" <appender name="info-out" class=&quo...

Java Language • log4j / log4j2