Tutorial by Examples: r

public class Singleton { private static final Singleton INSTANCE = new Singleton(); private Singleton() {} public static Singleton getInstance() { return INSTANCE; } } It can be argued that this example is effectively lazy initialization. Section 12.4.1 of ...

To increment date objects in Javascript, we can usually do this: var checkoutDate = new Date(); // Thu Jul 21 2016 10:05:13 GMT-0400 (EDT) checkoutDate.setDate( checkoutDate.getDate() + 1 ); console.log(checkoutDate); // Fri Jul 22 2016 10:05:13 GMT-0400 (EDT) It is possible to use setD...

To implement an item click listener and/or an item long click listener, you can create an interface in your adapter: public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.ViewHolder> { public interface OnItemClickListener { void onItemSeleted(int position, Vi...

countMatches method from org.apache.commons.lang3.StringUtils is typically used to count occurences of a substring or character in a String: import org.apache.commons.lang3.StringUtils; String text = "One fish, two fish, red fish, blue fish"; // count occurrences of a substring Str...

Method references allow predefined static or instance methods that adhere to a compatible functional interface to be passed as arguments instead of an anonymous lambda expression. Assume that we have a model: class Person { private final String name; private final String surname; ...

Start with an iterable which needs to be grouped lst = [("a", 5, 6), ("b", 2, 4), ("a", 2, 5), ("c", 2, 6)] Generate the grouped generator, grouping by the second element in each tuple: def testGroupBy(lst): groups = itertools.groupby(lst, key=lambda...

Scalars are Perl's most basic data type. They're marked with the sigil $ and hold a single value of one of three types: a number (3, 42, 3.141, etc.) a string ('hi', "abc", etc.) a reference to a variable (see other examples). my $integer = 3; # number my $str...

Arrays store an ordered sequence of values. You can access the contents by index, or iterate over them. The values will stay in the order you filled them in. my @numbers_to_ten = (1,2,3,4,5,6,7,8,9,10); # More conveniently: (1..10) my @chars_of_hello = ('h','e','l','l','o'); my @word_list = ('Hel...

HTML <p>My shadow always follows me.</p> CSS p { -webkit-filter: drop-shadow(10px 10px 1px green); filter: drop-shadow(10px 10px 1px green); } Result

To use multiple filters, separate each value with a space. HTML <img src='donald-duck.png' alt='Donald Duck' title='Donald Duck' /> CSS img { -webkit-filter: brightness(200%) grayscale(100%) sepia(100%) invert(100%); filter: brightness(200%) grayscale(100%) sepia(100%) invert(1...

HTML <img src='donald-duck.png' alt='Donald Duck' title='Donald Duck' /> CSS img { -webkit-filter: hue-rotate(120deg); filter: hue-rotate(120deg); } Result

HTML <div></div> CSS div { width: 100px; height: 100px; background-color: white; -webkit-filter: invert(100%); filter: invert(100%); } Result Turns from white to black.

HTML <img src='donald-duck.png' alt='Donald Duck' title='Donald Duck' /> CSS img { -webkit-filter: blur(1px); filter: blur(1px); } Result Makes you wanna rub your glasses.

Carousel components can be instantiated via jQuery with the function $('.carousel').carousel(options), where $('.carousel') is a top-level reference to the specific carousel and options is a Javascript object specifying the carousel's default attributes. The options object allows for multiple prope...

Generally you should avoid using the default database role (often postgres) in your application. You should instead create a user with lower levels of privileges. Here we make one called niceusername and give it a password very-strong-password CREATE ROLE niceusername with PASSWORD 'very-strong-pas...

If we want to iterate backwards through a list or vector we can use a reverse_iterator. A reverse iterator is made from a bidirectional, or random access iterator which it keeps as a member which can be accessed through base(). To iterate backwards use rbegin() and rend() as the iterators for the e...

The arc4random_uniform() function is the simplest way to get high-quality random integers. As per the manual: arc4random_uniform(upper_bound) will return a uniformly distributed random number less than upper_bound. arc4random_uniform() is recommended over constructions like ''arc4random() % uppe...

The following code demonstrates usage of arc4random_uniform() to generate a random integer between 3 and 12: uint32_t randomIntegerWithinRange = arc4random_uniform(10) + 3; // A random integer between 3 and 12 This works to create a range because arc4random_uniform(10) returns an integer between...

hash( (1, 2) ) # ok hash( ([], {"hello"}) # not ok, since lists and sets are not hashabe Thus a tuple can be put inside a set or as a key in a dict only if each of its elements can. { (1, 2) } # ok { ([], {"hello"}) ) # not ok

One of the most common use of Sed is text substitution that can be achieved with the s command. In a terminal, type echo "Hello sed" | sed 's/sed/World/' and press Enter: $ echo "Hello sed" | sed 's/sed/World/' Hello World "Hello World" should be output to the ter...