Tutorial by Examples: er

The method nextInt(int bound) of Random accepts an upper exclusive boundary, i.e. a number that the returned random value must be less than. However, only the nextInt method accepts a bound; nextLong, nextDouble etc. do not. Random random = new Random(); random.nextInt(1000); // 0 - 999 int num...

NSArray *array = [NSArray arrayWithObjects:@"Nick", @"Ben", @"Adam", @"Melissa", nil]; NSPredicate *aPredicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'a'"]; NSArray *beginWithA = [array filteredArrayUsingPredicate:bPredicate]; ...

Consider we have a class Animal which has a child class Dog class Animal { public Animal() { Console.WriteLine("In Animal's constructor"); } } class Dog : Animal { public Dog() { Console.WriteLine("In Dog's constructor"); } ...

Properties are members of an object. Each named property is a pair of (name, descriptor). The name is a string that allows access (using the dot notation object.propertyName or the square brackets notation object['propertyName']). The descriptor is a record of fields defining the bevahiour of the pr...

select LastName, FirstName, from Person Returns message: Error Code: 1064. You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'from Person' at line 2. Getting a "1064 error" message from MySQL mean...

By default error message appears below textbox in <div class="help-block"></div> on keyUp or after pressing submit button if any validation constraints aren't met. Sometimes we want a message on submit only i.e. no validation at onKeyup event. Let's check yii2/widgets/ActiveF...

A Kotlin interface contains declarations of abstract methods, and default method implementations although they cannot store state. interface MyInterface { fun bar() } This interface can now be implemented by a class as follows: class Child : MyInterface { override fun bar() { ...

An interface in Kotlin can have default implementations for functions: interface MyInterface { fun withImplementation() { print("withImplementation() was called") } } Classes implementing such interfaces will be able to use those functions without reimplementing cl...

There are several ways methods can be inherited public abstract class Car { public void HonkHorn() { // Implementation of horn being honked } // virtual methods CAN be overridden in derived classes public virtual void ChangeGear() { // Implementation of gear...

INSERT INTO `my_table` (`field_1`, `field_2`) VALUES ('data_1', 'data_2'), ('data_1', 'data_3'), ('data_4', 'data_5'); This is an easy way to add several rows at once with one INSERT statement. This kind of 'batch' insert is much faster than inserting rows one by one. Typically...

Java 8 provides classes called IntSummaryStatistics, DoubleSummaryStatistics and LongSummaryStatistics which give a state object for collecting statistics such as count, min, max, sum, and average. Java SE 8 List<Integer> naturalNumbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); IntSu...

Different data types for error/success def getPersonFromWebService(url: String): Either[String, Person] = { val response = webServiceClient.get(url) response.webService.status match { case 200 => { val person = parsePerson(response) if(!isVali...

To check for a precise number of elements in the collection def f(ints: Seq[Int]): String = ints match { case Seq() => "The Seq is empty !" case Seq(first) => s"The seq has exactly one element : $first" case Seq(first, second) => s"The...

All Java exceptions are instances of classes in the Exception class hierarchy. This can be represented as follows: java.lang.Throwable - This is the base class for all exception classes. Its methods and constructors implement a range of functionality common to all exceptions. java.lang.Excep...

$fruit1 = ['apples', 'pears']; $fruit2 = ['bananas', 'oranges']; $all_of_fruits = array_merge($fruit1, $fruit2); // now value of $all_of_fruits is [0 => 'apples', 1 => 'pears', 2 => 'bananas', 3 => 'oranges'] Note that array_merge will change numeric indexes, but overwrite string...

A context manager is an object that is notified when a context (a block of code) starts and ends. You commonly use one with the with statement. It takes care of the notifying. For example, file objects are context managers. When a context ends, the file object is closed automatically: open_file = ...

In Python 2, an iterator can be traversed by using a method called next on the iterator itself: Python 2.x2.3 g = (i for i in range(0, 3)) g.next() # Yields 0 g.next() # Yields 1 g.next() # Yields 2 In Python 3 the .next method has been renamed to .__next__, acknowledging its “magic” ro...

The null coalescing operator makes it easy to ensure that a method that may return null will fall back to a default value. Without the null coalescing operator: string name = GetName(); if (name == null) name = "Unknown!"; With the null coalescing operator: string name = GetN...

enum MyEnum { One, Two, Three } foreach(MyEnum e in Enum.GetValues(typeof(MyEnum))) Console.WriteLine(e); This will print: One Two Three

You can use a column's number (where the leftmost column is '1') to indicate which column to base the sort on, instead of describing the column by its name. Pro: If you think it's likely you might change column names later, doing so won't break this code. Con: This will generally reduce readabilit...