Tutorial by Examples: f

It is possible to generate a Stream that does not end. Calling a terminal method on an infinite Stream causes the Stream to enter an infinite loop. The limit method of a Stream can be used to limit the number of terms of the Stream that Java processes. This example generates a Stream of all natural...

The ArrayIndexOutOfBoundsException is thrown when a non-existing index of an array is being accessed. Arrays are zero-based indexed, so the index of the first element is 0 and the index of the last element is the array capacity minus 1 (i.e. array.length - 1). Therefore, any request for an array e...

The String type provides two methods for converting strings between upper case and lower case: toUpperCase to convert all characters to upper case toLowerCase to convert all characters to lower case These methods both return the converted strings as new String instances: the original String o...

To check whether a particular String a is being contained in a String b or not, we can use the method String.contains() with the following syntax: b.contains(a); // Return true if a is contained in b, false otherwise The String.contains() method can be used to verify if a CharSequence can be fou...

In order to get the length of a String object, call the length() method on it. The length is equal to the number of UTF-16 code units (chars) in the string. String str = "Hello, World!"; System.out.println(str.length()); // Prints out 13 Live Demo on Ideone A char in a String is UTF...

By using startActivityForResult(Intent intent, int requestCode) you can start another Activity and then receive a result from that Activity in the onActivityResult(int requestCode, int resultCode, Intent data) method. The result will be returned as an Intent. An intent can contain data via a Bundle ...

Let's say you want to define an interface that allows publishing / consuming data to and from different types of channels (e.g. AMQP, JMS, etc), but you want to be able to switch out the implementation details ... Let's define a basic IO interface that can be re-used across multiple implementations...

A Pattern can be compiled with flags, if the regex is used as a literal String, use inline modifiers: Pattern pattern = Pattern.compile("foo.", Pattern.CASE_INSENSITIVE | Pattern.DOTALL); pattern.matcher("FOO\n").matches(); // Is true. /* Had the regex not been compiled case...

All Javadoc comments begin with a block comment followed by an asterisk (/**) and end when the block comment does (*/). Optionally, each line can begin with arbitrary whitespace and a single asterisk; these are ignored when the documentation files are generated. /** * Fields can be documented as ...

Executors accept a java.lang.Runnable which contains (potentially computationally or otherwise long-running or heavy) code to be run in another Thread. Usage would be: Executor exec = anExecutor; exec.execute(new Runnable() { @Override public void run() { //offloaded work, no need t...

If your computation produces some return value which later is required, a simple Runnable task isn't sufficient. For such cases you can use ExecutorService.submit(Callable<T>) which returns a value after execution completes. The Service will return a Future which you can use to retrieve the r...

The ScheduledExecutorService class provides a methods for scheduling single or repeated tasks in a number of ways. The following code sample assume that pool has been declared and initialized as follows: ScheduledExecutorService pool = Executors.newScheduledThreadPool(2); In addition to the nor...

Maps provide methods which let you access the keys, values, or key-value pairs of the map as collections. You can iterate through these collections. Given the following map for example: Map<String, Integer> repMap = new HashMap<>(); repMap.put("Jon Skeet", 927_654); repMap.p...

import javax.xml.bind.annotation.XmlRootElement; @XmlRootElement public class User { private long userID; private String name; // getters and setters } By using the annotation XMLRootElement, we can mark a class as a root element of an XML file. import java.io.File; ...

To read an XML file named UserDetails.xml with the below content <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <user> <name>Jon Skeet</name> <userID>8884321</userID> </user> We need a POJO class named U...

Arrays are objects which provide space to store up to its size of elements of specified type. An array's size can not be modified after the array is created. int[] arr1 = new int[0]; int[] arr2 = new int[2]; int[] arr3 = new int[]{1, 2, 3, 4}; int[] arr4 = {1, 2, 3, 4, 5, 6, 7}; int len1 = ar...

A float is a single-precision 32-bit IEEE 754 floating point number. By default, decimals are interpreted as doubles. To create a float, simply append an f to the decimal literal. double doubleExample = 0.5; // without 'f' after digits = double float floatExample = 0.5f; // with 'f' aft...

Don't just use Optional.get() since that may throw NoSuchElementException. The Optional.orElse(T) and Optional.orElseGet(Supplier<? extends T>) methods provide a way to supply a default value in case the Optional is empty. String value = "something"; return Optional.ofNullable(v...

Use the orElseThrow() method of Optional to get the contained value or throw an exception, if it hasn't been set. This is similar to calling get(), except that it allows for arbitrary exception types. The method takes a supplier that must return the exception to be thrown. In the first example, the...

filter() is used to indicate that you would like the value only if it matches your predicate. Think of it like if (!somePredicate(x)) { x = null; }. Code examples: String value = null; Optional.ofNullable(value) // nothing .filter(x -> x.equals("cool string"))// this is nev...