make barcode with vb.net Answers to Quizzes and Exercises in Visual C#

Generating ANSI/AIM Code 128 in Visual C# Answers to Quizzes and Exercises

Appendix: Answers to Quizzes and Exercises
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Example A-33. One solution to Exercise 12-4 (continued)
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Console.Write(", "); ((Foot)myMeter).OutputFoot( ); Console.WriteLine( ); } static void Main(string[] args) { Tester t = new Tester( ); t.Run( ); } } }
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13: Interfaces
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Quiz Solutions
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Solution to Question 13-1. The interface defines the methods, properties, and so forth that the implementing class must provide. The implementing class provides these members and, optionally, additional members. Solution to Question 13-2. Every class has exactly one base class (either explicit, or the object class by default), but may implement zero, one, or more interfaces. An abstract base class serves as the base to a derived class that must implement all of its abstract methods; otherwise, that derived class is also abstract. Solution to Question 13-3. You can t create an instance of an interface. To access the interface methods, you must create an instance of a class that implements the interface. Solution to Question 13-4. You d use the following syntax to create a class that inherits from a parent and implements two interfaces:
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class MyClass : MyBase, ISuppose, IDo {...}
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Note that the base class must come first after the colon. Solution to Question 13-5. The is and as operators are used to test whether a class implements an interface. Solution to Question 13-6. is returns a Boolean, which is false if the interface is not implemented. as attempts to make the cast, unlike is, and returns null if the cast fails. Using the as operator can be more efficient.
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13: Interfaces |
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Solution to Question 13-7. Extending an interface is very much like deriving a class. The new interface inherits all the members of the parent interface, and can also include additional methods. Solution to Question 13-8. The syntax for extending an interface is:
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ExtendedInterface : OriginalInterface
For example, you would read:
ILoggedCompressible : ICompressible
as ILoggedCompressible extends ICompressible. Solution to Question 13-9. The class implementing a method of the interface can mark that method virtual, and the implementation of the method can then be overridden in derived classes. Solution to Question 13-10. Explicit interface implementation identifies the member of the interface by naming the interface itself (e.g., IStorable.Write( )). This is done to differentiate implementation methods when there might otherwise be an ambiguity, such as when implementing multiple interfaces that have methods with the same signature.
Exercise Solutions
Solution to Exercise 13-1. Define an interface IConvertible that indicates that the class can convert a string to C# or VB. The interface should have two methods: ConvertToCSharp and ConvertToVB. Each method should take a string and return a string. In this exercise, you re not actually creating code that will run; you re just defining the interface. As you learned, the methods of the interface don t have any implementation, they just have signatures. Example A-34 shows this simple interface.
Example A-34. One solution to Exercise 13-1
using using using using System; System.Collections.Generic; System.Linq; System.Text;
namespace Exercise_13_1 { interface IConvertible { string ConvertToCSharp(string stringToConvert); string ConvertToVB(string stringToConvert); } }
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Appendix: Answers to Quizzes and Exercises
Solution to Exercise 13-2. Implement that interface and test it by creating a class ProgramHelper that implements IConvertible. You don t have to write methods to convert the string; just use simple string messages to simulate the conversion. Test your new class with a string of fake code to make sure it works. In this exercise, you ll actually implement the interface that you derived earlier, although your code doesn t need to do anything more than say that it s converting the string. The string we used in Run( ) is just dummy text representing a string of VB code. In Run( ), we pass the string to the ConvertToVB( ) method, and then pass it back to the ConvertToCSharp( ) method. Example A-35 shows the way we did it.
Example A-35. Our solution to Exercise 13-2
using using using using System; System.Collections.Generic; System.Linq; System.Text;
namespace Exercise_13_2 { interface IConvertible { string ConvertToCSharp(string stringToConvert); string ConvertToVB(string stringToConvert); } public class ProgramHelper : IConvertible { public ProgramHelper( ) // constructor { Console.WriteLine("Creating ProgramHelper"); } public string ConvertToCSharp(string stringToConvert) { Console.WriteLine("Converting the string you passed in to CSharp syntax"); return "This is a C# String."; } public string ConvertToVB(string stringToConvert) { Console.WriteLine("Converting the string you passed in to VB syntax"); return "This is a VB String."; } } class Tester { public void Run( ) { // Create a ProgramHelper object ProgramHelper theProgramHelper = new ProgramHelper( );
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