CS2_35_GUI_Events_Parts1_2

CS2_35_GUI_Events_Parts1_2 - CS2 • Module 35 • Category...

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Unformatted text preview: CS2 • Module 35 • Category: Elements of Java • Topic: GUI Events • Objectives – Events – Interclass Communication CS 2 Introduction to Object Oriented Programming Module 35 Elements of Java GUI Events Nota Bene This lecture presentation contains a number of "hidden" slides. Feel free to read, study and learn from them on your own! Today's Plan for Fun • Events – What is an event? – Simple (?) Example • Swing Components – JFrames – JComponents – An example – Swing Component Design (MVC/UI-Delegate) Events • Behind the scenes, the Java runtime environment is monitoring many things • When any of a number of things happen an event is said to occur. Sometimes the terminology is “an event gets fired" • Examples of the types of things that can "fire" events – Pressing a key on the keyboard – Clicking on a component (like a button) – Entering a component with the mouse pointer – Have a timer "time-out" Events • Moving the mouse around any reasonably complicated GUI can literally cause hundreds if not thousands of events to occur • Events will be ignored except for the ones that you tell Java that you are interested in doing something about • Java maintains a data structure of all the events that you have decided to handle and looks up events and does what you tell it to do. Remember this??? import java.awt.*; public class HelloGUI { public static void main (String[ ] arg) { System.out.println("About to make GUI"); Frame f = new Frame ("Hello GUIs"); f.setSize( 200, 200 ); f.show(); System.out.println("Finished making GUI"); }// main }// class HelloGUI What didn't work??? Making it work • Determine which event occurs when the "Close the Window" button is pressed – The API is your friend – The lecture notes are your friend – Hint: In this case it's an event called "Window Closing" • You decide what class is going to handle this event – It might be the actual class which has the window – It can be any other class • Write the method (and class?) that will handle the event. When this event occurs, Java is going to go to the class that you identify as the event handler or Listener . It will look for a method called: public void windowClosing(WindowEvent e) • Java will report an error to you if this class doesn't have this method. How might the designers of Java be guaranteed that you will implement this method? An Interface!!! // Note: found in java.awt.event public interface WindowListener extends EventListener { void windowActivated(WindowEvent e); void windowClosed(WindowEvent e); void windowClosing(WindowEvent e); void windowDeactivated(WindowEvent e); void windowDeiconified(WindowEvent e); void windowIconified(WindowEvent e); void windowOpened(WindowEvent e); } So we could write a class like this import java.awt.*; import java.awt.event.*; public class Handler implements WindowListener { public void windowActivated(WindowEvent e) {} public void windowClosed(WindowEvent e) {} public void windowClosing(WindowEvent e)...
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CS2_35_GUI_Events_Parts1_2 - CS2 • Module 35 • Category...

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