visual basic 2010 barcode generator Adapter Classes in Java

Printer QR Code in Java Adapter Classes

Adapter Classes
Creating QR Code In Java
Using Barcode maker for Java Control to generate, create QR Code image in Java applications.
Quick Response Code Reader In Java
Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications.
Java provides a special feature, called an adapter class, that can simplify the creation of event handlers in certain situations An adapter class provides an empty implementation of all methods in an event listener interface Adapter classes are useful when you want to receive and process only some of the events that are handled by a particular event listener interface You can define a new class to act as an event listener by extending one of the adapter classes and implementing only those events in which you are interested For example, the MouseMotionAdapter class has two methods, mouseDragged( ) and mouseMoved( ) The signatures of these empty methods are exactly as defined in the MouseMotionListener interface If you were interested in only mouse drag events, then you could simply extend MouseMotionAdapter and implement mouseDragged( ) The empty implementation of mouseMoved( ) would handle the mouse motion events for you Table 20-4 lists the different adapter classes in javaawtevent and notes the interface that each implements
Bar Code Generation In Java
Using Barcode printer for Java Control to generate, create barcode image in Java applications.
Barcode Recognizer In Java
Using Barcode decoder for Java Control to read, scan read, scan image in Java applications.
- 462 -
Generating QR Code In Visual C#.NET
Using Barcode generation for .NET framework Control to generate, create QR Code image in VS .NET applications.
QR Code 2d Barcode Creation In .NET Framework
Using Barcode printer for ASP.NET Control to generate, create QR-Code image in ASP.NET applications.
The following example demonstrates an adapter It displays a message in the status bar of an applet viewer or browser when the mouse is clicked or dragged However, all other mouse events are silently ignored The program has three classes AdapterDemo extends Applet Its init( ) method creates an instance of MyMouseAdapter and registers that object to receive notifications of mouse events It also creates an instance of MyMouseMotionAdapter and registers that object to receive notifications of mouse motion events Both of the constructors take a reference to the applet as an argument MyMouseAdapter implements the mouseClicked( ) method The other mouse events are silently ignored by code inherited from the MouseAdapter class Table 20-4 Listener Interfaces Implemented by Adapter Classes
Create QR Code 2d Barcode In .NET Framework
Using Barcode printer for .NET framework Control to generate, create QR Code JIS X 0510 image in VS .NET applications.
Creating QR Code 2d Barcode In Visual Basic .NET
Using Barcode creator for VS .NET Control to generate, create QR Code 2d barcode image in Visual Studio .NET applications.
Adapter Class
Encode Bar Code In Java
Using Barcode creation for Java Control to generate, create barcode image in Java applications.
Paint Barcode In Java
Using Barcode printer for Java Control to generate, create bar code image in Java applications.
Listener Interface
Drawing UCC-128 In Java
Using Barcode creation for Java Control to generate, create EAN128 image in Java applications.
Linear 1D Barcode Creator In Java
Using Barcode encoder for Java Control to generate, create 1D image in Java applications.
ComponentAdapter ContainerAdapter FocusAdapter KeyAdapter MouseAdapter MouseMotionAdapter WindowAdapter
Create USPS Confirm Service Barcode In Java
Using Barcode printer for Java Control to generate, create USPS Confirm Service Barcode image in Java applications.
Scanning Data Matrix 2d Barcode In None
Using Barcode scanner for Software Control to read, scan read, scan image in Software applications.
ComponentListener ContainerListener FocusListener KeyListener MouseListener MouseMotionListener WindowListener
Decoding EAN-13 In .NET Framework
Using Barcode decoder for .NET Control to read, scan read, scan image in Visual Studio .NET applications.
Data Matrix Creation In None
Using Barcode generator for Microsoft Excel Control to generate, create ECC200 image in Office Excel applications.
MyMouseMotionAdapter implements the mouseDragged( ) method The other mouse motion event is silently ignored by code inherited from the MouseMotionAdapter class Note that both of our event listener classes save a reference to the applet This information is provided as an argument to their constructors and is used later to invoke the showStatus( ) method // Demonstrate an adapter import javaawt*; import javaawtevent*; import javaapplet*; /* <applet code="AdapterDemo" width=300 height=100> </applet> */ public class AdapterDemo extends Applet { public void init() { addMouseListener(new MyMouseAdapter(this)); addMouseMotionListener(new MyMouseMotionAdapter(this)); }
Make Code 128 In Visual Basic .NET
Using Barcode generation for .NET Control to generate, create Code128 image in .NET framework applications.
Painting Matrix 2D Barcode In .NET
Using Barcode maker for ASP.NET Control to generate, create Matrix Barcode image in ASP.NET applications.
- 463 -
Read Code 3/9 In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
ANSI/AIM Code 39 Scanner In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
} class MyMouseAdapter extends MouseAdapter { AdapterDemo adapterDemo; public MyMouseAdapter(AdapterDemo adapterDemo) { thisadapterDemo = adapterDemo; } // Handle mouse clicked public void mouseClicked(MouseEvent me) { adapterDemoshowStatus("Mouse clicked"); }
class MyMouseMotionAdapter extends MouseMotionAdapter { AdapterDemo adapterDemo; public MyMouseMotionAdapter(AdapterDemo adapterDemo) { thisadapterDemo = adapterDemo; } // Handle mouse dragged public void mouseDragged(MouseEvent me) { adapterDemoshowStatus("Mouse dragged"); }
As you can see by looking at the program, not having to implement all of the methods defined by the MouseMotionListener and MouseListener interfaces saves you a considerable amount of effort and prevents your code from becoming cluttered with empty methods As an exercise, you might want to try rewriting one of the keyboard input examples shown earlier so that it uses a KeyAdapter
Inner Classes
In 7, the basics of inner classes were explained Here you will see why they are important Recall that an inner class is a class defined within other class, or even within an expression This section illustrates how inner classes can be used to simplify the code when using event adapter classes To understand the benefit provided by inner classes, consider the applet shown in the following listing It does not use an inner class Its goal is to display the string "Mouse Pressed" in the status bar of the applet viewer or browser when the mouse is pressed There are two top-level classes in this program MousePressedDemo extends Applet, and MyMouseAdapter extends MouseAdapter The init( ) method of MousePressedDemo instantiates MyMouseAdapter and provides this object as an argument to the addMouseListener( ) method Notice that a reference to the applet is supplied as an argument to the MyMouseAdapter constructor This reference is stored in an instance variable for later use by the mousePressed( ) method When the mouse is pressed, it invokes the showStatus( ) method of the applet through the stored applet reference In other words, showStatus( ) is invoked relative to the applet reference stored by MyMouseAdapter // This applet does NOT use an inner class import javaapplet*; import javaawtevent*; /* <applet code="MousePressedDemo" width=200 height=100> </applet> */
- 464 -
public class MousePressedDemo extends Applet { public void init() { addMouseListener(new MyMouseAdapter(this)); } } class MyMouseAdapter extends MouseAdapter { MousePressedDemo mousePressedDemo; public MyMouseAdapter(MousePressedDemo mousePressedDemo) { thismousePressedDemo = mousePressedDemo; } public void mousePressed(MouseEvent me) { mousePressedDemoshowStatus("Mouse Pressed"); } } The following listing shows how the preceding program can be improved by using an inner class Here, InnerClassDemo is a top-level class that extends Applet MyMouseAdapter is an inner class that extends MouseAdapter Because MyMouseAdapter is defined within the scope of InnerClassDemo, it has access to all of the variables and methods within the scope of that class Therefore, the mousePressed( ) method can call the showStatus( ) method directly It no longer needs to do this via a stored reference to the applet Thus, it is no longer necessary to pass MyMouseAdapter( ) a reference to the invoking object // Inner class demo import javaapplet*; import javaawtevent*; /* <applet code="InnerClassDemo" width=200 height=100> </applet> */ public class InnerClassDemo extends Applet { public void init() { addMouseListener(new MyMouseAdapter()); } class MyMouseAdapter extends MouseAdapter { public void mousePressed(MouseEvent me) { showStatus("Mouse Pressed"); } } }
Copyright © OnBarcode.com . All rights reserved.