UNIT III Event Handling of the car j.pptx

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1. UNIT – III EVENT HANDLING Unit Outcomes (UOs): - 3a. Use delegation event model for given problem  . 3b.Use AWT/Swing component(s) to handle given event. 3c.Use Adapter classes to solve the problem. 3d. Use Inner Classes to solve given problem. Total Marks=12    

2. UNIT-III EVENT HANDING The Delegation Event Model: • The modern approach to handling events is based on the delegation event model , which defines standard and consistent mechanisms to generate and process events. Concept is quite simple: a source generates an event and sends it to one or more listeners . In this scheme, the listener simply waits until it receives an event. Once received, the listener processes the event and then returns. In the delegation event model, listeners must register with a source in order to receive an event notification. This provides an important benefit: notifications are sent only to listeners that want to receive them.

3. The Delegation Event Model:

4. Events In the delegation model, an event is an object that describes a state change in a source. It can be generated as a consequence of a person interacting with the elements in a graphical user interface. Some of the activities that cause events to be generated are pressing a button, entering a character via the keyboard, selecting an item in a list, and clicking the mouse. Many other user operations could also be cited as examples. Events may also occur that are not directly caused by interactions with a user interface. For example, an event may be generated when a timer expires, a counter exceeds a value, a software or hardware failure occurs, or an operation is completed. You are free to define events that are appropriate for your application.

5. PART-II [unit-III] Advance JAVA Programming (22517) Computer Engineering / IT Program Group (CO/CM/IF/CW) Mrs. Manjula Athani HOD - Computer Engineering Email: [email protected]

6. Event Sources A source is an object that generates an event. This occurs when the internal state of that object changes in some way. Sources may generate more than one type of event. A source must register listeners in order for the listeners to receive notifications about a specific type of event. Each type of event has its own registration method. Here is the general form: public void add Type Listener ( Type Listener el ) Here, Type is the name of the event and el is a reference to the event listener. For example, the method that registers a keyboard event listener is called addKeyListener ( ) . The method that registers a mouse motion listener is called addMouseMotionListener ( ) .

7. Here, Type is the name of the event and el is a reference to the event listener. For example, to remove a keyboard listener, you would call removeKeyListener ( ) . The methods that add or remove listeners are provided by the source that generates events. For example, the Component class provides methods to add and remove keyboard and mouse event listeners.

8. Event Sources An event source is the object that generates the event. For example if you click a button an ActionEvent object is generated. The object of the ActionEvent class has all corresponding information about this event. Here button is an event source. Various event sources can be button, checkbox, textbox, scrollbars and so on.

9. Event Listeners The task of handling an event is carried out by event listener. When an event occurs, first of all an event object of the appropriate type is created. This object is then passed to a Listener. A listener must implement the interface that has the method for event handling. The java.awt.event package contains definitions of all event classes and listener interface.

10. An Interface contains constant values and method declaration. The methods in an interface are only declared and not implemented, i.e. the methods do not have a body. The interfaces are used to define behaviour on occurrence of event that can be implemented by any class anywhere in the class hierarchy.

11. Event Classes Event classes are the classes responsible for handling events in the event handling mechanism. The EventObject class is at the top of the event class hierarchy. It belongs to the java.util package. And other event classes are present in java.awt.event package. The getSource () and toString () are the methods of the EventObject class. There is getId () method belonging to java.awt.event For example , if a keyboard event occurs, you can find out whether the event was key press or key release from the event object.

12. java.awt.event

13. PART-III [unit-III] Advance JAVA Programming (22517) Computer Engineering / IT Program Group (CO/CM/IF/CW) Mrs. Manjula Athani HOD - Computer Engineering Email: [email protected]

14. Various event classes that are defined in java.awt.event class are - An ActionEvent object is generated when a component is activated. For example if a button is pressed or a menu item is selected then this event occurs. An AdjustmentEvent object is generated when scrollbars are used. A TextEvent object is generated when text of a component or a text field is changed. A ContainerEvent object is generated when component are added or removed from container. A ComponentEvent object is generated when a component is resized, moved, hidden or made visible.

15. An ItemEvent is generated when an item from a list is selected. For example a choice is made or if checkbox is selected. A FocusEvent object is generated when component receives keyboard focus for input. A KeyEvent object is generated when key on keyboard is pressed or released. A WindowEvent object is generated when a window activated, maximized or minimized. A MouseEvent object is generated when a mouse is clicked, moved, dragged, released .

16. PART-IV [unit-III] Advance JAVA Programming (22517) Computer Engineering / IT Program Group (CO/CM/IF/CW) Manjula Athani HOD - Computer Engineering Email: [email protected]

17. Following are the fields for java.awt.event.MouseEvent class : static int MOUSE_CLICKED --The "mouse clicked" event static int MOUSE_DRAGGED --The "mouse dragged" event static int MOUSE_ENTERED --The "mouse entered" event static int MOUSE_EXITED --The "mouse exited" event static int MOUSE_MOVED --The "mouse moved" event static int MOUSE_PRESSED -- The "mouse pressed" event static int MOUSE_RELEASED --The "mouse released" event

18. Keyboard Events. When key from a keyboard is pressed then it causes an event. There are three commonly used methods from KeyListener interface and those are keyPressed (), keyReleased () and keyTyped (). The keyPressed () event is for handling the event of pressing a key, similarly keyReleased () event is for handling the event of release of key. Using keyTyped () method we can display the character typed on the screen. The only needed method for this is getKeyChar () which returns the currently typed character.

19. PART-V [unit-III] Advance JAVA Programming (22517) Computer Engineering / IT Program Group (CO/CM/IF/CW) Mrs. Manjula Athani HOD - Computer Engineering Email: [email protected]

20. EventListener Interfaces The task of handling an event is carried out by event listener. When an event occurs, first of all an event object of the appropriate type is created. This object is then passed to a Listener. A listener must implement the interface that has the method for event handling. The java.awt.event package contains definitions of all event classes and listener interface. An Interface contains constant values and method declaration. The methods in an interface are only declared and not implemented, i.e. the methods do not have a body. The interfaces are used to define behavior on occurrence of event that can be implemented by any class anywhere in the class hierarchy.

21. ActionListener Interface This interface defines the method actionPerformed () which is invoked when an ActionEvent occurs. The syntax of this method is void actionPerformed ( ActionEvent act) where act is an object of ActionEvent class.

22. ItemListener Interface This interface is used when an item from a list is selected. For example a choice is made or if checkbox is selected. The itemStateChanged () is the only method defined by the ItemListener interface. The syntax is void itemStateChanged ( ItemEvent It)

23. KeyListener Interface This interface is defining the events such as keyPressed (), keyReleased () and keyTyped () are used. These methods are useful for key press, key release and when you type some characters. void keyPressed ( keyEvent k) void keyReleased ( keyEvent k) void keyTyped ( keyEvent k)

24. MouseListener Interface This interface defines five important methods for various activities such as mouse click, press, released, entered or exited. These are void mouseClicked ( MouseEvent m) void mousePressed ( MouseEvent m) void mouseReleased ( MouseEvent m) void mouseEntered ( MouseEvent m) void mouseExited ( MouseEvent m) Methods of MouseMotionListener interface The signature of 2 methods found in MouseMotionListener interface are given below: void  mouseDragged ( MouseEvent  e);   void  mouseMoved ( MouseEvent  e);  

25. MouseMotion Interface For handling mouse drag and mouse move events the required methods are defined by MouseMotionListener interface. These methods are void mouseDragged ( MouseEvent m) void mouseMoved ( MouseEvent m)

26. TextListener Interface An event of type TextEvent is generated when a value in textfield or textarea is entered or edited. The methods used by TextListener Interface are public String paramString (): public void textValueChanged ( TextEvent e):

27. WindowListener Interface There are seven methods in which are related to windows activation and deactivation. void windowOpened ( WindowEvent w) void windowClosed ( WindowEvent w) void windowClosing ( WindowEvent w) void windowActivated ( WindowEvent w) void windowDeactivated ( WindowEvent w) void windowIconified ( WindowEvent w) void windowDeiconified ( WindowEvent w)

28. PART-VI [unit-III] Advance JAVA Programming (22517) Computer Engineering / IT Program Group (CO/CM/IF/CW) Mrs. Manjula Athani HOD - Computer Engineering Email: [email protected]

29. Adapter Classes It is basically a class in Java that implements an interface with a set of dummy methods. The famous adapter classes in Java API are WindowAdapter, ComponentAdapter, ContainerAdapter, FocusAdapter, KeyAdapter, MouseAdapter and MouseMotionAdapter. Whenever your class implements such interface, you have to implements all of the seven methods. WindowAdapter class implements WindowListener interface and make seven empty implementation.

30. Inner classes: Java inner class is a class within class is called inner class or interface. Without existing one type of object there is no chance of existing another type of object then we should go for inner class. Example: University consists of several departments without existing university there is no chance of existing department hence we have to declare department class inside university class. class university { class department { } } NOTE:WITHOUT EXISTING OUTER CLASS OBJECT THERE IS NO CHANCE OF EXISTING INNER CLASS OBJECT . OUTER CLASS INNER CLASS

31. Based on position of declaration and behavior all Inner lasses are devided into 4 types. 1.Normal inner class 2.Method Local inner class 3.Anonymous inner class 4.Static nested class

32. 1.Normal inner class: If you are declaring any named class directly inside a class without static modifiers such type of inner class is called normal inner class. Class Outer { Class Inner { } } Internal working of Java member inner class The java compiler creates two class files in case of inner class. The class file name of inner class is "Outer$Inner". If you want to instantiate inner class, you must have to create the instance of outer class. In such case, instance of inner class is created inside the instance of outer class. After compiling i.e Javac Outer.java Creates two class files 1.Outer.class 2.Outer$Inner.class

33. Method local Inner classes. Sometimes we can declare a class inside a method such type of Inner classes are called method Local Inner classes. The main purpose of method local inner class is to define method specific repeatedly required functionality method. Local method inner classes are best suitable to meet nested method requirement public class MethodLocal { public void m1(){ class Inner { public void sum(int x,int y) { System.out.println("The SUM:"+(x+y)); } } Inner i=new Inner(); i.sum(10,20); i.sum(100,200); i.sum(1000,2000); } public static void main(String args[]) { MethodLocal m=new MethodLocal(); m.m1(); } }

34. Java Anonymous inner class Sometimes we can declare inner class without name such type inner classes are called anonymous Inner classes. The main purpose of anonymous inner class is just use of one time usage. Java anonymous inner class example using class abstract class Person{     abstract void eat();   }   class TestAnonymousInner {    public static void main(String args[]) {     Person p=new Person() {     void eat() { System.out.println("nice fruits");}     };     p.eat();    }   }  

35. Java static nested class A static class i.e. created inside a class is called static nested class in java. It cannot access non-static data members and methods. It can be accessed by outer class name. It can access static data members of outer class including private. Static nested class cannot access non-static (instance) data member or method. Java static nested class example with instance method class TestOuter1 {     static int data=30;     static class Inner{      void msg() { System.out.println("data is "+data);}     }     public static void main(String args[]) {     TestOuter1.Inner obj=new TestOuter1.Inner();     obj.msg();     }   }   Output: data is 30