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extremetech Hacking BlackBerry phần 8

Phần này của mã bắt đầu với khai báo lớp cho HelloBlackBerry. Lưu ý rằng HelloBlackBerry mở rộng một lớp học được gọi là UIApplication. Bất kỳ ứng dụng BlackBerry cung cấp một giao diện người dùng mở rộng UIApplication, một lớp học BlackBerry được tìm thấy trong gói net.rim.device.api.ui (vì thế các báo cáo nhập khẩu đầu tiên). | Chapter 11 Developing Your Own BlackBerry Applications 183 main application class. The main class is a standard part of every BlackBerry application. In this project the main class is called HelloBlackBerry public class HelloBlackBerry extends UiApplication public static void main String args HelloBlackBerry theApp new HelloBlackBerry theApp.enterEventDispatcher public HelloBlackBerry pushScreen new HelloScreen This section of code begins with the class declaration for HelloBlackBerry. Note that HelloBlackBerry extends a class called UiApplication. Any BlackBerry application that provides a user interface extends UiApplication a BlackBerry class found in the net.rim.device.api.ui package hence the first import statement . The extends keyword is basis for inheritance in Java. So essentially with this first line you are saying I am declaring a new class HelloBlackBerry and I wish it to inherit all of the behaviors found in the UiApplication class. All BlackBerry programs start at a special function called main so it stands to reason that the main program class HelloBlackBerry should have a main method.The code public static void main String args signifies that the HelloBlackBerry class has a main method and that the lines of code in main will be executed at program startup. In this simple HelloBlackBerry program main does the bare minimum job of creating an instance of the HelloBlackBerry class and starting the necessary event-handling process by calling enterEventDispatcher . Doing this allows a BlackBerry program to listen in on and participate in system events and messages and is a standard part of any BlackBerry application. The other piece of your HelloBlackBerry class is the constructor. All classes have a constructor which is the place where an instance of a class can perform any tasks that must be taken care of when the instance comes to life within a program. In the HelloBlackBerry program the constructor does one thing launches the user interface for itself