Package codedraw

Class EventScanner

java.lang.Object
codedraw.EventScanner
All Implemented Interfaces:
Iterable<Event>
public class EventScanner extends Object implements Iterable<Event>
The EventScanner can be used to handle events that are produced in CodeDraw. There is two ways to consume events from the EventScanner, either through the Iterable<Event> interface or through the Scanner like structure by calling has- and next-methods.

The example below displays the current mouse position and the amount the mouse has been pressed. Before each frame is drawn all events that happened between the previous frame and the current frame are processed by a foreach loop. Each event inside that foreach loop is then processed based on the type of the event. If it is a MouseMoveEvent then the position is saved, if it is a MouseClickEvent then the clickCount is increased. All other event types are discarded in the default branch. 

 CodeDraw cd = new CodeDraw();

 int mouseX = 0;
 int mouseY = 0;
 int clickCount = 0;

 while (!es.isClosed()) {
     for (var e : cd.getEventScanner()) {
         switch (e) {
             case MouseMoveEvent a -> {
                 mouseX = a.getX();
                 mouseY = a.getY();
             }
             case MouseClickEvent a -> clickCount++;
             default -> { }
         }
     }

     cd.clear();
     cd.drawText(100, 100, "Position: " + x + " " + y + "\nClick: " + clickCount);
     cd.show();
 }


If you use an older version of Java you can utilize the Scanner like properties of the EventScanner. The inner while loop in the example below processes all currently available events. In each iteration a new event will be at the head of the queue and the inner while loop will only stop once all currently available events are consumed. Inside the inner loop depending on which type of event is at the head of the queue one branch of the if/else will be selected. If the head of the queue is a MouseMoveEvent event the hasMouseMoveEvent() method will return true and then the nextMouseMoveEvent() method will be called which returns the MouseMoveEvent from the head of the queue. All other events inside the queue will then shift forward and there will be a new event at the head of the queue. Do not forget to call the next method because otherwise the program will enter an endless loop because the same event will always be at the head of the queue. After the MouseMoveEvent has been returned from the nextMouseMoveEvent() method the event can be used to update the state of the program. In this case it just updates the current mouse position. After all currently available events are processed the changes are displayed by clearing the canvas and then calling the drawText method. 

 CodeDraw cd = new CodeDraw();
 EventScanner es = cd.getEventScanner();
 int mouseX = 0;
 int mouseY = 0;
 int clickCount = 0;

 while (!es.isClosed()) {
     while (es.hasEventNow()) {
         if (es.hasMouseMoveEvent()) {
             MouseMoveEvent a = es.nextMouseMoveEvent();
             mouseX = a.getX();
             mouseY = a.getY();
         }
         else if (es.hasMouseClickEvent()) {
             es.nextEvent();
             clickCount++;
         }
         else {
             es.nextEvent();
         }
     }

     cd.clear();
     cd.drawText(100, 100, "Position: " + mouseX + " " + mouseY + "\nClick: " + clickCount);
     cd.show();
 }


Common mistakes when using the EventScanner:
  • The next method is not called within an if branch.
  • When consuming more than two events ifs are used instead of elseif.
  • The last else branch is forgotten and the remaining events are not discarded.
When a CodeDraw window is closed all remaining events can still be consumed from the EventScanner but no new events will appear.

  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    hasEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    boolean
    hasEventNow()
    Compared to hasEvent() this method does not wait until the next event is available, but instead returns immediately.
    boolean
    hasKeyDownEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    boolean
    hasKeyPressEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    boolean
    hasKeyUpEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    boolean
    hasMouseClickEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    boolean
    hasMouseDownEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    boolean
    hasMouseEnterEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    boolean
    hasMouseLeaveEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    boolean
    hasMouseMoveEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    boolean
    hasMouseUpEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    boolean
    hasMouseWheelEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    boolean
    hasWindowCloseEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    boolean
    hasWindowMoveEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    Iterator<Event>
    iterator()
    Creates an iterator containing all the currently available events.
    Event
    nextEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    KeyDownEvent
    nextKeyDownEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    KeyPressEvent
    nextKeyPressEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    KeyUpEvent
    nextKeyUpEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    MouseClickEvent
    nextMouseClickEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    MouseDownEvent
    nextMouseDownEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    MouseEnterEvent
    nextMouseEnterEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    MouseLeaveEvent
    nextMouseLeaveEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    MouseMoveEvent
    nextMouseMoveEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    MouseUpEvent
    nextMouseUpEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    MouseWheelEvent
    nextMouseWheelEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    WindowCloseEvent
    nextWindowCloseEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    WindowMoveEvent
    nextWindowMoveEvent()
    Waits until the next event is available or returns immediately if there is an event in the EventScanner already.
    void
    removeEventsOlderThan(Duration duration)
    Removes all events that are older than the duration given as a parameter.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    Methods inherited from interface java.lang.Iterable

    forEach, spliterator

  • Method Details

    • hasEventNow

      public boolean hasEventNow()
      Compared to hasEvent() this method does not wait until the next event is available, but instead returns immediately. If there is currently an event available returns true otherwise false.
      Returns:
      whether there are currently events available

    • hasEvent

      public boolean hasEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. Returns false if there are no more events, true otherwise.
      Returns:
      whether there are more events available

    • hasMouseClickEvent

      public boolean hasMouseClickEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. Returns true if the next event is a mouse click event, otherwise false. The mouse click event is triggered once every time a mouse button is pressed down and quickly released again.
      Returns:
      whether the next event is a mouse click event.

    • hasMouseMoveEvent

      public boolean hasMouseMoveEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. Returns true if the next event is a mouse move event, otherwise false. The mouse move event is triggered continuously while the mouse is being moved.
      Returns:
      whether the next event is a mouse move event.

    • hasMouseDownEvent

      public boolean hasMouseDownEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. Returns true if the next event is a mouse down event, otherwise false. The mouse down event is triggered exactly once every time a mouse button is pressed down.
      Returns:
      whether the next event is a mouse down event.

    • hasMouseUpEvent

      public boolean hasMouseUpEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. Returns true if the next event is a mouse up event, otherwise false. The mouse up event is triggered every time a mouse button is released.
      Returns:
      whether the next event is a mouse up event.

    • hasMouseEnterEvent

      public boolean hasMouseEnterEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. Returns true if the next event is a mouse enter event, otherwise false. The mouse enter event is triggered every time the mouse enters the canvas.
      Returns:
      whether the next event is a mouse enter event.

    • hasMouseLeaveEvent

      public boolean hasMouseLeaveEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. Returns true if the next event is a mouse leave event, otherwise false. The mouse leave event is triggered every time the mouse leaves the canvas.
      Returns:
      whether the next event is a mouse leave event.

    • hasMouseWheelEvent

      public boolean hasMouseWheelEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. Returns true if the next event is a mouse wheel event, otherwise false. The mouse wheel event is triggered each time the mouse wheel is turned.
      Returns:
      whether the next event is a mouse wheel event.

    • hasKeyDownEvent

      public boolean hasKeyDownEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. Returns true if the next event is a key down event, otherwise false. The key down event is triggered exactly once every time a key is pressed down.
      Returns:
      whether the next event is a key down event.

    • hasKeyUpEvent

      public boolean hasKeyUpEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. Returns true if the next event is a key up event, otherwise false. The key up event is triggered exactly once every time a key is released.
      Returns:
      whether the next event is a key up event.

    • hasKeyPressEvent

      public boolean hasKeyPressEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. Returns true if the next event is a key press event, otherwise false. The key press event is triggered continuously while a key is being held down.
      Returns:
      whether the next event is a key press event.

    • hasWindowMoveEvent

      public boolean hasWindowMoveEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. Returns true if the next event is a window move event, otherwise false. The window move event is triggered every time the CodeDraw window is moved.
      Returns:
      whether the next event is a window move event.

    • hasWindowCloseEvent

      public boolean hasWindowCloseEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. Returns true if the next event is a window close event, otherwise false. The window close event is triggered exactly once after the user closes the window or CodeDraw.close() is called.
      Returns:
      whether the next event is a window close event.

    • nextEvent

      public Event nextEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. The event is returned as a generic Event object which is one of the twelve event subtypes. Check hasEvent() or hasEventNow() before calling this function.

      You can use this method to either discard events or use the switch type matching feature of Java. 
      
 while (es.hasEventNow()) {
     switch (es.nextEvent()) {
         case MouseDownEventArgs a:
             System.out.println("The mouse has been pressed at x=" + a.getX() + " y=" + a.getY() + ".");
             break;
         case KeyDownEventArgs a:
             System.out.println("The " + a.getKey() + " has been pressed.");
             break;
         default:
             break;
     }
 }
      Returns:
      The next available event.
      Throws:
      NoSuchElementException - if there are no more events.

    • nextMouseClickEvent

      public MouseClickEvent nextMouseClickEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. If the event is a mouse click event the event is returned otherwise an InputMismatchException is thrown. The mouse click event is triggered once every time a mouse button is pressed down and quickly released again. Check hasMouseClickEvent() before calling this function.
      Returns:
      a mouse click event.
      Throws:
      InputMismatchException - if the next event is not a mouse click event.
      NoSuchElementException - if there are no more events.

    • nextMouseMoveEvent

      public MouseMoveEvent nextMouseMoveEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. If the event is a mouse move event the event is returned otherwise an InputMismatchException is thrown. The mouse move event is triggered continuously while the mouse is being moved. Check hasMouseMoveEvent() before calling this function.
      Returns:
      a mouse move event.
      Throws:
      InputMismatchException - if the next event is not a mouse move event.
      NoSuchElementException - if there are no more events.

    • nextMouseDownEvent

      public MouseDownEvent nextMouseDownEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. If the event is a mouse down event the event is returned otherwise an InputMismatchException is thrown. The mouse down event is triggered exactly once every time a mouse button is pressed down. Check hasMouseDownEvent() before calling this function.
      Returns:
      a mouse down event.
      Throws:
      InputMismatchException - if the next event is not a mouse down event.
      NoSuchElementException - if there are no more events.

    • nextMouseUpEvent

      public MouseUpEvent nextMouseUpEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. If the event is a mouse up event the event is returned otherwise an InputMismatchException is thrown. The mouse up event is triggered every time a mouse button is released. Check hasMouseUpEvent() before calling this function.
      Returns:
      a mouse up event.
      Throws:
      InputMismatchException - if the next event is not a mouse up event.
      NoSuchElementException - if there are no more events.

    • nextMouseEnterEvent

      public MouseEnterEvent nextMouseEnterEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. If the event is a mouse enter event the event is returned otherwise an InputMismatchException is thrown. The mouse enter event is triggered every time the mouse enters the canvas. Check hasMouseEnterEvent() before calling this function.
      Returns:
      a mouse enter event.
      Throws:
      InputMismatchException - if the next event is not a mouse enter event.
      NoSuchElementException - if there are no more events.

    • nextMouseLeaveEvent

      public MouseLeaveEvent nextMouseLeaveEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. If the event is a mouse leave event the event is returned otherwise an InputMismatchException is thrown. The mouse leave event is triggered every time the mouse leaves the canvas. Check hasMouseLeaveEvent() before calling this function.
      Returns:
      a mouse leave event.
      Throws:
      InputMismatchException - if the next event is not a mouse leave event.
      NoSuchElementException - if there are no more events.

    • nextMouseWheelEvent

      public MouseWheelEvent nextMouseWheelEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. If the event is a mouse wheel event the event is returned otherwise an InputMismatchException is thrown. The mouse wheel event is triggered each time the mouse wheel is turned. Check hasMouseWheelEvent() before calling this function.
      Returns:
      a mouse wheel event.
      Throws:
      InputMismatchException - if the next event is not a mouse wheel event.
      NoSuchElementException - if there are no more events.

    • nextKeyDownEvent

      public KeyDownEvent nextKeyDownEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. If the event is a key down event the event is returned otherwise an InputMismatchException is thrown. The key down event is triggered exactly once every time a key is pressed down. Check hasKeyDownEvent() before calling this function.
      Returns:
      a key down event.
      Throws:
      InputMismatchException - if the next event is not a key down event.
      NoSuchElementException - if there are no more events.

    • nextKeyUpEvent

      public KeyUpEvent nextKeyUpEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. If the event is a key up event the event is returned otherwise an InputMismatchException is thrown. The key up event is triggered exactly once every time a key is released. Check hasKeyUpEvent() before calling this function.
      Returns:
      a key up event.
      Throws:
      InputMismatchException - if the next event is not a key up event.
      NoSuchElementException - if there are no more events.

    • nextKeyPressEvent

      public KeyPressEvent nextKeyPressEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. If the event is a key press event the event is returned otherwise an InputMismatchException is thrown. The key press event is triggered continuously while a key is being held down. Check hasKeyPressEvent() before calling this function.
      Returns:
      a key press event.
      Throws:
      InputMismatchException - if the next event is not a key press event.
      NoSuchElementException - if there are no more events.

    • nextWindowMoveEvent

      public WindowMoveEvent nextWindowMoveEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. If the event is a window move event the event is returned otherwise an InputMismatchException is thrown. The window move event is triggered every time the CodeDraw window is moved. Check hasWindowMoveEvent() before calling this function.
      Returns:
      a window move event.
      Throws:
      InputMismatchException - if the next event is not a window move event.
      NoSuchElementException - if there are no more events.

    • nextWindowCloseEvent

      public WindowCloseEvent nextWindowCloseEvent()
      Waits until the next event is available or returns immediately if there is an event in the EventScanner already. If the event is a window close event the event is returned otherwise an InputMismatchException is thrown. The window close event is triggered exactly once after the user closes the window or CodeDraw.close() is called. Check hasWindowCloseEvent() before calling this function.
      Returns:
      a window close event.
      Throws:
      InputMismatchException - if the next event is not a window close event.
      NoSuchElementException - if there are no more events.

    • removeEventsOlderThan

      public void removeEventsOlderThan(Duration duration)
      Removes all events that are older than the duration given as a parameter.
      Parameters:
      duration - any duration.

    • iterator

      public Iterator<Event> iterator()
      Creates an iterator containing all the currently available events. By calling this method all events in the EventScanner are consumed and the EventScanner will be empty until new events are generated.
      Specified by:
      iterator in interface Iterable<Event>
      Returns:
      An event iterator.