Tutorial by Examples: s

You can get the value of other primitive data types as a String using one the String class's valueOf methods. For example: int i = 42; String string = String.valueOf(i); //string now equals "42”. This method is also overloaded for other datatypes, such as float, double, boolean, and ...

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...

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...

The toString() method is used to create a String representation of an object by using the object´s content. This method should be overridden when writing your class. toString() is called implicitly when an object is concatenated to a string as in "hello " + anObject. Consider the followin...

String str = "My String"; System.out.println(str.charAt(0)); // "M" System.out.println(str.charAt(1)); // "y" System.out.println(str.charAt(2)); // " " System.out.println(str.charAt(str.length-1)); // Last character "g" To get the nth charac...

TL;DR == tests for reference equality (whether they are the same object) .equals() tests for value equality (whether they are logically "equal") equals() is a method used to compare two objects for equality. The default implementation of the equals() method in the Object class returns...

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...

A short is a 16-bit signed integer. It has a minimum value of -215 (-32,768), and a maximum value of 215 ‑1 (32,767) short example = -48; short myShort = 987; short anotherShort = 17; short addedShorts = (short) (myShort + anotherShort); // 1,004 short subtractedShorts = (short) (myShort - an...

Server: Start, and wait for incoming connections //Open a listening "ServerSocket" on port 1234. ServerSocket serverSocket = new ServerSocket(1234); while (true) { // Wait for a client connection. // Once a client connected, we get a "Socket" object // that c...

By default, any files that you save to Internal Storage are private to your application. They cannot be accessed by other applications, nor the user under normal circumstances. These files are deleted when the user uninstalls the application. To Write Text to a File String fileName= "hellowor...

Buttons fire action events when they are activated (e.g. clicked, a keybinding for the button is pressed, ...). button.setOnAction(new EventHandler<ActionEvent>() { @Override public void handle(ActionEvent event) { System.out.println("Hello World!"); } }); ...

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...

When a Java class overrides the equals method, it should override the hashCode method as well. As defined in the method's contract: Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, ...

By default, WebView does not implement JavaScript alert dialogs, ie. alert() will do nothing. In order to make you need to firstly enable JavaScript (obviously..), and then set a WebChromeClient to handle requests for alert dialogs from the page: webView.setWebChromeClient(new WebChromeClient() { ...

Since Java 6, the recommended way to access an SQL-based database in Java is via the JDBC(Java DataBase Connectivity) API. This API comes in two packagages: java.sql and javax.sql. JDBC defines database interactions in terms of Connections and Drivers. A Driver interacts with the database, and pr...

Once we've gotten the Connection, we will mostly use it to create Statement objects. Statements represent a single SQL transaction; they are used to execute a query, and retrieve the results (if any). Let's look at some examples: public void useConnection() throws SQLException{ Connection ...

OptionalDouble, OptionalInt and OptionalLong work like Optional, but are specifically designed to wrap primitive types: OptionalInt presentInt = OptionalInt.of(value); OptionalInt absentInt = OptionalInt.empty(); Because numeric types do have a value, there is no special handling for null. Empt...