import javafx.beans.binding.Bindings;
import javafx.beans.binding.StringBinding;
import javafx.beans.property.BooleanProperty;
import javafx.beans.property.ReadOnlyBooleanProperty;
import javafx.beans.property.ReadOnlyObjectProperty;
import javafx.beans.property.SimpleBooleanProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.beans.value.ObservableStringValue;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.event.EventTarget;
import javafx.event.EventType;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Node;
import javafx.scene.control.Button;
import javafx.scene.control.ContentDisplay;
import javafx.scene.control.ToggleButton;
import javafx.scene.input.KeyCode;
import javafx.scene.input.KeyEvent;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Priority;
import javafx.scene.layout.VBox;
import javafx.scene.shape.PolygonBuilder;

public class VirtualKeyboard {
  private final VBox root ;
  
  /**
   * Creates a Virtual Keyboard. 
   * @param target The node that will receive KeyEvents from this keyboard. 
   * If target is null, KeyEvents will be dynamically forwarded to the focus owner
   * in the Scene containing this keyboard.
   */
  public VirtualKeyboard(ReadOnlyObjectProperty<Node> target) {
    this.root = new VBox(5);
    root.setPadding(new Insets(10));
    root.getStyleClass().add("virtual-keyboard");

    final Modifiers modifiers = new Modifiers();

    // Data for regular buttons; split into rows
    final String[][] unshifted = new String[][] {
        { "`", "1", "2", "3", "4", "5", "6", "7", "8", "9", "0", "-", "=" },
        { "q", "w", "e", "r", "t", "y", "u", "i", "o", "p", "[", "]", "\\" },
        { "a", "s", "d", "f", "g", "h", "j", "k", "l", ";", "'" },
        { "z", "x", "c", "v", "b", "n", "m", ",", ".", "/" } };

    final String[][] shifted = new String[][] {
        { "~", "!", "@", "#", "$", "%", "^", "&", "*", "(", ")", "_", "+" },
        { "Q", "W", "E", "R", "T", "Y", "U", "I", "O", "P", "{", "}", "|" },
        { "A", "S", "D", "F", "G", "H", "J", "K", "L", ":", "\"" },
        { "Z", "X", "C", "V", "B", "N", "M", "<", ">", "?" } };

    final KeyCode[][] codes = new KeyCode[][] {
        { KeyCode.BACK_QUOTE, KeyCode.DIGIT1, KeyCode.DIGIT2, KeyCode.DIGIT3,
            KeyCode.DIGIT4, KeyCode.DIGIT5, KeyCode.DIGIT6, KeyCode.DIGIT7,
            KeyCode.DIGIT8, KeyCode.DIGIT9, KeyCode.DIGIT0, KeyCode.SUBTRACT,
            KeyCode.EQUALS },
        { KeyCode.Q, KeyCode.W, KeyCode.E, KeyCode.R, KeyCode.T, KeyCode.Y,
            KeyCode.U, KeyCode.I, KeyCode.O, KeyCode.P, KeyCode.OPEN_BRACKET,
            KeyCode.CLOSE_BRACKET, KeyCode.BACK_SLASH },
        { KeyCode.A, KeyCode.S, KeyCode.D, KeyCode.F, KeyCode.G, KeyCode.H,
            KeyCode.J, KeyCode.K, KeyCode.L, KeyCode.SEMICOLON, KeyCode.QUOTE },
        { KeyCode.Z, KeyCode.X, KeyCode.C, KeyCode.V, KeyCode.B, KeyCode.N,
            KeyCode.M, KeyCode.COMMA, KeyCode.PERIOD, KeyCode.SLASH } };

    // non-regular buttons (don't respond to Shift)
    final Button escape = createNonshiftableButton("Esc", KeyCode.ESCAPE, modifiers, target);
    final Button backspace = createNonshiftableButton("Backspace", KeyCode.BACK_SPACE, modifiers, target);
    final Button delete = createNonshiftableButton("Del", KeyCode.DELETE, modifiers, target);
    final Button enter = createNonshiftableButton("Enter", KeyCode.ENTER,  modifiers, target);
    final Button tab = createNonshiftableButton("Tab", KeyCode.TAB, modifiers, target);

    // Cursor keys, with graphic instead of text
    final Button cursorLeft = createCursorKey(KeyCode.LEFT, modifiers, target, 15.0, 5.0, 15.0, 15.0, 5.0, 10.0);
    final Button cursorRight = createCursorKey(KeyCode.RIGHT, modifiers, target, 5.0, 5.0, 5.0, 15.0, 15.0, 10.0);
    final Button cursorUp = createCursorKey(KeyCode.UP, modifiers, target, 10.0, 0.0, 15.0, 10.0, 5.0, 10.0);
    final Button cursorDown = createCursorKey(KeyCode.DOWN, modifiers, target, 10.0, 10.0, 15.0, 0.0, 5.0, 0.0);
    final VBox cursorUpDown = new VBox(2);
    cursorUpDown.getChildren().addAll(cursorUp, cursorDown);

    // "Extras" to go at the left or right end of each row of buttons.
    final Node[][] extraLeftButtons = new Node[][] { {escape}, {tab}, {modifiers.capsLockKey()}, {modifiers.shiftKey()} };
    final Node[][] extraRightButtons = new Node[][] { {backspace}, {delete}, {enter}, {modifiers.secondShiftKey()} };

    // build layout
    for (int row = 0; row < unshifted.length; row++) {
      HBox hbox = new HBox(5);
      hbox.setAlignment(Pos.CENTER);
      root.getChildren().add(hbox);

      hbox.getChildren().addAll(extraLeftButtons[row]);
      for (int k = 0; k < unshifted[row].length; k++) {
        hbox.getChildren().add( createShiftableButton(unshifted[row][k], shifted[row][k], codes[row][k], modifiers, target));
      }
      hbox.getChildren().addAll(extraRightButtons[row]);
    }

    final Button spaceBar = createNonshiftableButton(" ", KeyCode.SPACE, modifiers, target);
    spaceBar.setMaxWidth(Double.POSITIVE_INFINITY);
    HBox.setHgrow(spaceBar, Priority.ALWAYS);

    final HBox bottomRow = new HBox(5);
    bottomRow.setAlignment(Pos.CENTER);
    bottomRow.getChildren().addAll(modifiers.ctrlKey(), modifiers.altKey(),
        modifiers.metaKey(), spaceBar, cursorLeft, cursorUpDown, cursorRight);
    root.getChildren().add(bottomRow);    
  }
  
  /**
   * Creates a VirtualKeyboard which uses the focusProperty of the scene to which it is attached as its target
   */
  public VirtualKeyboard() {
    this(null);
  }
  
  /**
   * Visual component displaying this keyboard. The returned node has a style class of "virtual-keyboard".
   * Buttons in the view have a style class of "virtual-keyboard-button".
   * @return a view of the keyboard.
   */
  public Node view() {
    return root ;
  }
  
  // Creates a "regular" button that has an unshifted and shifted value
  private Button createShiftableButton(final String unshifted, final String shifted,
      final KeyCode code, Modifiers modifiers, final ReadOnlyObjectProperty<Node> target) {
    final ReadOnlyBooleanProperty letter = new SimpleBooleanProperty( unshifted.length() == 1 && Character.isLetter(unshifted.charAt(0)));
    final StringBinding text = 
        Bindings.when(modifiers.shiftDown().or(modifiers.capsLockOn().and(letter)))
        .then(shifted)
        .otherwise(unshifted);
    Button button = createButton(text, code, modifiers, target);
    return button;
  }

  // Creates a button with fixed text not responding to Shift
  private Button createNonshiftableButton(final String text, final KeyCode code, final Modifiers modifiers, final ReadOnlyObjectProperty<Node> target) {
    StringProperty textProperty = new SimpleStringProperty(text);
    Button button = createButton(textProperty, code, modifiers, target);
    return button;
  }
  
  // Creates a button with mutable text, and registers listener with it
  private Button createButton(final ObservableStringValue text, final KeyCode code, final Modifiers modifiers, final ReadOnlyObjectProperty<Node> target) {
    final Button button = new Button();
    button.textProperty().bind(text);
        
    // Important not to grab the focus from the target:
    button.setFocusTraversable(false);
    
    // Add a style class for css:
    button.getStyleClass().add("virtual-keyboard-button");
    
    button.setOnAction(new EventHandler<ActionEvent>() {
      @Override
      public void handle(ActionEvent event) {

        final Node targetNode ;
        if (target != null) {
          targetNode = target.get();
        } else {
          targetNode = view().getScene().getFocusOwner();
        }
        
        if (targetNode != null) {
          final String character;
          if (text.get().length() == 1) {
            character = text.get();
          } else {
            character = KeyEvent.CHAR_UNDEFINED;
          }
          final KeyEvent keyPressEvent = createKeyEvent(button, targetNode, KeyEvent.KEY_PRESSED, character, code, modifiers);
          targetNode.fireEvent(keyPressEvent);
          final KeyEvent keyReleasedEvent = createKeyEvent(button, targetNode, KeyEvent.KEY_RELEASED, character, code, modifiers);
          targetNode.fireEvent(keyReleasedEvent);
          if (character != KeyEvent.CHAR_UNDEFINED) {
            final KeyEvent keyTypedEvent = createKeyEvent(button, targetNode, KeyEvent.KEY_TYPED, character, code, modifiers);
            targetNode.fireEvent(keyTypedEvent);
          }
          modifiers.releaseKeys();
        }
      }
    });
    return button;
  }

  // Utility method to create a KeyEvent from the Modifiers
  private KeyEvent createKeyEvent(Object source, EventTarget target,
      EventType<KeyEvent> eventType, String character, KeyCode code,
      Modifiers modifiers) {
    return new KeyEvent(source, target, eventType, character, code.toString(),
        code, modifiers.shiftDown().get(), modifiers.ctrlDown().get(),
        modifiers.altDown().get(), modifiers.metaDown().get());
  }
  
  // Utility method for creating cursor keys:
  private Button createCursorKey(KeyCode code, Modifiers modifiers, ReadOnlyObjectProperty<Node> target, Double... points) {
    Button button = createNonshiftableButton("", code, modifiers, target);
    final Node graphic = PolygonBuilder.create().points(points).build();
    graphic.setStyle("-fx-fill: -fx-mark-color;");
    button.setGraphic(graphic);
    button.setContentDisplay(ContentDisplay.GRAPHIC_ONLY);
    return button ;
  }
  
  // Convenience class to bundle together the modifier keys and their selected state
  private static class Modifiers {
    private final ToggleButton shift;
    private final ToggleButton shift2;
    private final ToggleButton ctrl;
    private final ToggleButton alt;
    private final ToggleButton meta;
    private final ToggleButton capsLock;

    Modifiers() {
      this.shift = createToggle("Shift");
      this.shift2 = createToggle("Shift");
      this.ctrl = createToggle("Ctrl");
      this.alt = createToggle("Alt");
      this.meta = createToggle("Meta");
      this.capsLock = createToggle("Caps");

      shift2.selectedProperty().bindBidirectional(shift.selectedProperty());
    }

    private ToggleButton createToggle(final String text) {
      final ToggleButton tb = new ToggleButton(text);
      tb.setFocusTraversable(false);
      return tb;
    }

    public Node shiftKey() {
      return shift;
    }

    public Node secondShiftKey() {
      return shift2;
    }

    public Node ctrlKey() {
      return ctrl;
    }

    public Node altKey() {
      return alt;
    }

    public Node metaKey() {
      return meta;
    }

    public Node capsLockKey() {
      return capsLock;
    }

    public BooleanProperty shiftDown() {
      return shift.selectedProperty();
    }

    public BooleanProperty ctrlDown() {
      return ctrl.selectedProperty();
    }

    public BooleanProperty altDown() {
      return alt.selectedProperty();
    }

    public BooleanProperty metaDown() {
      return meta.selectedProperty();
    }

    public BooleanProperty capsLockOn() {
      return capsLock.selectedProperty();
    }

    public void releaseKeys() {
      shift.setSelected(false);
      ctrl.setSelected(false);
      alt.setSelected(false);
      meta.setSelected(false);
    }
  }  
}
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About

Java online compiler

Write, Run & Share Java code online using OneCompiler's Java online compiler for free. It's one of the robust, feature-rich online compilers for Java language, running the Java LTS version 17. Getting started with the OneCompiler's Java editor is easy and fast. The editor shows sample boilerplate code when you choose language as Java and start coding.

Taking inputs (stdin)

OneCompiler's Java online editor supports stdin and users can give inputs to the programs using the STDIN textbox under the I/O tab. Using Scanner class in Java program, you can read the inputs. Following is a sample program that shows reading STDIN ( A string in this case ).

import java.util.Scanner;
class Input {
    public static void main(String[] args) {
    	Scanner input = new Scanner(System.in);
    	System.out.println("Enter your name: ");
    	String inp = input.next();
    	System.out.println("Hello, " + inp);
    }
}

Adding dependencies

OneCompiler supports Gradle for dependency management. Users can add dependencies in the build.gradle file and use them in their programs. When you add the dependencies for the first time, the first run might be a little slow as we download the dependencies, but the subsequent runs will be faster. Following sample Gradle configuration shows how to add dependencies

apply plugin:'application'
mainClassName = 'HelloWorld'

run { standardInput = System.in }
sourceSets { main { java { srcDir './' } } }

repositories {
    jcenter()
}

dependencies {
    // add dependencies here as below
    implementation group: 'org.apache.commons', name: 'commons-lang3', version: '3.9'
}

About Java

Java is a very popular general-purpose programming language, it is class-based and object-oriented. Java was developed by James Gosling at Sun Microsystems ( later acquired by Oracle) the initial release of Java was in 1995. Java 17 is the latest long-term supported version (LTS). As of today, Java is the world's number one server programming language with a 12 million developer community, 5 million students studying worldwide and it's #1 choice for the cloud development.

Syntax help

Variables

short x = 999; 			// -32768 to 32767
int   x = 99999; 		// -2147483648 to 2147483647
long  x = 99999999999L; // -9223372036854775808 to 9223372036854775807

float x = 1.2;
double x = 99.99d;

byte x = 99; // -128 to 127
char x = 'A';
boolean x = true;

Loops

1. If Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
  // code
} else {
  // code
}

Example:

int i = 10;
if(i % 2 == 0) {
  System.out.println("i is even number");
} else {
  System.out.println("i is odd number");
}

2. Switch:

Switch is an alternative to If-Else-If ladder and to select one among many blocks of code.

switch(<conditional-expression>) {    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
...    
    
default:     
 //code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition. Usually for loop is preferred when number of iterations is known in advance.

for(Initialization; Condition; Increment/decrement){  
    //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while(<condition>){  
 // code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {
  // code 
} while (<condition>);

Classes and Objects

Class is the blueprint of an object, which is also referred as user-defined data type with variables and functions. Object is a basic unit in OOP, and is an instance of the class.

How to create a Class:

class keyword is required to create a class.

Example:

class Mobile {
    public:    // access specifier which specifies that accessibility of class members 
    string name; // string variable (attribute)
    int price; // int variable (attribute)
};

How to create a Object:

Mobile m1 = new Mobile();

How to define methods in a class:

public class Greeting {
    static void hello() {
        System.out.println("Hello.. Happy learning!");
    }

    public static void main(String[] args) {
        hello();
    }
}

Collections

Collection is a group of objects which can be represented as a single unit. Collections are introduced to bring a unified common interface to all the objects.

Collection Framework was introduced since JDK 1.2 which is used to represent and manage Collections and it contains:

  1. Interfaces
  2. Classes
  3. Algorithms

This framework also defines map interfaces and several classes in addition to Collections.

Advantages:

  • High performance
  • Reduces developer's effort
  • Unified architecture which has common methods for all objects.
CollectionDescription
SetSet is a collection of elements which can not contain duplicate values. Set is implemented in HashSets, LinkedHashSets, TreeSet etc
ListList is a ordered collection of elements which can have duplicates. Lists are classified into ArrayList, LinkedList, Vectors
QueueFIFO approach, while instantiating Queue interface you can either choose LinkedList or PriorityQueue.
DequeDeque(Double Ended Queue) is used to add or remove elements from both the ends of the Queue(both head and tail)
MapMap contains key-values pairs which don't have any duplicates. Map is implemented in HashMap, TreeMap etc.