Tutorial by Examples: r

Arrays are objects, but their type is defined by the type of the contained objects. Therefore, one cannot just cast A[] to T[], but each A member of the specific A[] must be cast to a T object. Generic example: public static <T, A> T[] castArray(T[] target, A[] array) { for (int i = 0; i...

Letters 3.0 let letters = CharacterSet.letters let phrase = "Test case" let range = phrase.rangeOfCharacter(from: letters) // range will be nil if no letters is found if let test = range { print("letters found") } else { print("letters not found") }...

A common question is how to juxtapose (combine) physically separate geographical regions on the same map, such as in the case of a choropleth describing all 50 American states (The mainland with Alaska and Hawaii juxtaposed). Creating an attractive 50 state map is simple when leveraging Google Maps...

Java doesn't provide a direct method in java.util.Arrays to remove an element from an array. To perform it, you can either copy the original array to a new one without the element to remove or convert your array to another structure allowing the removal. Using ArrayList You can convert the array t...

The + symbol marks a type parameter as covariant - here we say that "Producer is covariant on A": trait Producer[+A] { def produce: A } A covariant type parameter can be thought of as an "output" type. Marking A as covariant asserts that Producer[X] <: Producer[Y] prov...

By default all type parameters are invariant - given trait A[B], we say that "A is invariant on B". This means that given two parametrizations A[Cat] and A[Animal], we assert no sub/superclass relationship between these two types - it does not hold that A[Cat] <: A[Animal] nor that A[Ca...

The - symbol marks a type parameter as contravariant - here we say that "Handler is contravariant on A": trait Handler[-A] { def handle(a: A): Unit } A contravariant type parameter can be thought of as an "input" type. Marking A as contravariant asserts that Handler[X] &l...

Because collections are typically covariant in their element type*, a collection of a subtype may be passed where a super type is expected: trait Animal { def name: String } case class Dog(name: String) extends Animal object Animal { def printAnimalNames(animals: Seq[Animal]) = { anima...

Java provides specialized Streams for three types of primitives IntStream (for ints), LongStream (for longs) and DoubleStream (for doubles). Besides being optimized implementations for their respective primitives, they also provide several specific terminal methods, typically for mathematical operat...

The static keyword means 2 things: This value does not change from object to object but rather changes on a class as a whole Static properties and methods don't require an instance. public class Foo { public Foo{ Counter++; NonStaticCounter++; } public st...

The following is a timer that fires at a fixed interval. It's timeout is defined by Period and it invokes a callback defined by Timerfcn upon timeout. t = timer; t.TasksToExecute = Inf; t.Period = 0.01; % timeout value in seconds t.TimerFcn = @(myTimerObj, thisEvent)disp('hello'); % timer callba...

// Obtain an instance of JavaScript engine ScriptEngineManager manager = new ScriptEngineManager(); ScriptEngine engine = manager.getEngineByName("JavaScript"); //String to be evaluated String str = "3+2*4+5"; //Value after doing Arithmetic operation with operator preceden...

A struct can simply be copied using assignment. type T struct { I int S string } // initialize a struct t := T{1, "one"} // make struct copy u := t // u has its field values equal to t if u == t { // true fmt.Println("u and t are equal") // Prints: &qu...

This pattern is a more strict approach to starting an Activity. Its purpose is to improve code readability, while at the same time decrease code complexity, maintenance costs, and coupling of your components. The following example implements the starter pattern, which is usually implemented as a st...

The if construct (called a block IF statement in FORTRAN 77) is common across many programming languages. It conditionally executes one block of code when a logical expression is evaluated to true. [name:] IF (expr) THEN block [ELSE IF (expr) THEN [name] block] [ELSE [name] block] ...

Suppose you have a simple Customer model: class Customer(models.Model): first_name = models.CharField(max_length=255) last_name = models.CharField(max_length=255) is_premium = models.BooleanField(default=False) You register it in the Django admin and add search field by first_name...

In this example we aim to accomplish one of the most common tasks: I have a small DC motor laying around, how do I use my Arduino to control it? Easy, with PWM and serial communication, using the function analogWrite() and the Serial library. The basics Pulse Width Modulation or PWM for short is a...

Interceptors are used to intercept OkHttp calls. The reason to intercept could be to monitor, rewrite and retry calls. It can be used for outgoing request or incoming response both. class LoggingInterceptor implements Interceptor { @Override public Response intercept(Interceptor.Chain chain) thr...

private static final Interceptor REWRITE_CACHE_CONTROL_INTERCEPTOR = new Interceptor() { @Override public Response intercept(Interceptor.Chain chain) throws IOException { Response originalResponse = chain.proceed(chain.request()); return originalResponse.newBuilder() .header(&q...

class Foo { private string[] cities = new[] { "Paris", "London", "Berlin" }; public string this[int index] { get { return cities[index]; } set { cities[index] = value; } } } Usage...