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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...

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 primitive data type such as int holds values directly into the variable that is using it, meanwhile a variable that was declared using Integer holds a reference to the value. According to java API: "The Integer class wraps a value of the primitive type int in an object. An object of type Int...

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!"); } }); ...

Buttons can have a graphic. graphic can be any JavaFX node, like a ProgressBar button.setGraphic(new ProgressBar(-1)); An ImageView button.setGraphic(new ImageView("images/icon.png")); Or even another button button.setGraphic(new Button("Nested button"));

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...

Enum can be considered to be syntax sugar for a sealed class that is instantiated only a number of times known at compile-time to define a set of constants. A simple enum to list the different seasons would be declared as follows: public enum Season { WINTER, SPRING, SUMMER, FA...

An enum can contain a method, just like any class. To see how this works, we'll declare an enum like this: public enum Direction { NORTH, SOUTH, EAST, WEST; } Let's have a method that returns the enum in the opposite direction: public enum Direction { NORTH, SOUTH, EAST, WEST; ...

String getText(String url) throws IOException { HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection(); //add headers to the connection, or check the status if desired.. // handle error response code it occurs int responseCode = conn.getResponseCod...

The Standard Edition of Java comes with some annotations predefined. You do not need to define them by yourself and you can use them immediately. They allow the compiler to enable some fundamental checking of methods, classes and code. @Override This annotation applies to a method and says that th...

One use of SharedPreferences is to implement a "Settings" screen in your app, where the user can set their preferences / options. Like this: A PreferenceScreen saves user preferences in SharedPreferences. To create a PreferenceScreen, you need a few things: An XML file to define the av...