An Overview of Visual Basic.NET: A History and a Demonstration

Transcription

1 OVERVIEW o b j e c t i v e s This overview contains basic definitions and background information, including: A brief history of programming languages An introduction to the terminology used in object-oriented programming languages A Visual Basic.NET demonstration Information on using the tutorials effectively An Overview of Visual Basic.NET: A History and a Demonstration A Brief History of Programming Languages Although computers appear to be amazingly intelligent machines, they cannot yet think on their own. Computers still rely on human beings to give them directions. These directions are called programs, and the people who write the programs are called programmers. Just as human beings communicate with each other through the use of languages such as English, Spanish, Hindi, and Chinese, programmers use a variety of special languages, called programming languages, to communicate with the computer. Some popular programming languages are Visual Basic, Visual Basic.NET, C#.NET, C++, Java, Perl (Practical Extraction and Report Language), C, and COBOL (Common Business Oriented Language). In the next sections, you follow the progression of programming languages from machine languages to assembly languages, then to procedure-oriented high-level languages, and finally to object-oriented high-level languages.

2 VB 2 overview A Brief History of Programming Languages Machine Languages Within a computer, all data is represented by microscopic electronic switches that can be either off or on. The off switch is designated by a 0, and the on switch is designated by a 1. Because computers can understand only these on and off switches, the first programmers had to write the program instructions using nothing but combinations of 0s and 1s. Instructions written in 0s and 1s are called machine language or machine code. The machine languages (each type of machine has its own language) represent the only way to communicate directly with the computer. Figure 1 shows a segment of a program written in a machine language ƒƒ100000ƒƒ001101ƒƒ ƒƒƒ10001ƒƒƒ ƒƒ001ƒƒ11000ƒƒ ƒƒ00110 Figure 1: A segment of a program written in a machine language As you can imagine, programming in machine language is very tedious and error-prone and requires highly trained programmers. Assembly Languages Slightly more advanced programming languages are called assembly languages. Figure 2 shows a segment of a program written in an assembly language. mainƒprocƒpay movƒax,ƒdseg movƒax,ƒ0b00h addƒax,ƒdx movƒa1,ƒb1 mulƒb1,ƒax movƒb1,ƒ04h Figure 2: A segment of a program written in an assembly language The assembly languages simplify the programmer s job by allowing the programmer to use mnemonics in place of the 0s and 1s in the program. Mnemonics are memory aids in this case, alphabetic abbreviations for instructions. For example,

3 An Overview of Visual Basic.NET overview VB 3 most assembly languages use the mnemonic ADD to represent an add operation and the mnemonic MUL to represent a multiply operation. The mnemonic MOV is used to move data from one area of the computer s memory to another. Programs written in an assembly language require an assembler, which also is a program, to convert the assembly instructions into machine code the 0s and 1s the computer can understand. Although it is much easier to write programs in assembly language than in machine language, programming in assembly language still is tedious and requires highly trained programmers. High-Level Languages High-level languages, which allow the programmer to use instructions that more closely resemble the English language, represent the next major development in programming languages. Programs written in a high-level language require either an interpreter or a compiler to convert the English-like instructions into the 0s and 1s the computer can understand. Like assemblers, both interpreters and compilers are separate programs. An interpreter translates the high-level instructions into machine code, line by line, as the program is running, whereas a compiler translates the entire program into machine code before running the program. Like their predecessors, the first high-level languages were procedure-oriented. Procedure-Oriented High-Level Languages In procedure-oriented high-level languages, the emphasis of a program is on how to accomplish a task. The programmer must instruct the computer every step of the way, from the start of the task to its completion. The programmer determines and controls the order in which the computer processes the instructions. Examples of procedure-oriented high-level languages include COBOL, BASIC (Beginner s All- Purpose Symbolic Instruction Code), and C. Figure 3 shows a segment of a program written in BASIC. Notice how closely most of the instructions resemble the English language. Even if you do not know the BASIC language, it is easy to see that the program shown in Figure 3 tells the computer, step by step, how to compute and display an employee s net pay. inputƒ"enterƒname";names$ inputƒ"enterƒhours worked";hours inputƒ"enterƒpay rate";rate grosspayƒ=ƒhoursƒ*ƒrate federaltaxƒ=ƒ.2ƒ*ƒgrosspay socsectaxƒ=ƒ.07ƒ*ƒgrosspay statetaxƒ=ƒ.06ƒ*ƒgrosspay netpayƒ=ƒgrosspayƒ-ƒfederaltaxƒ-ƒsocsectaxƒ-ƒstatetax printƒnames$,ƒnetpay end Figure 3: A program written in BASIC a procedure-oriented high-level language

4 VB 4 overview A Brief History of Programming Languages In all procedure-oriented programs, the order of the instructions is extremely important. For example, in the program shown in Figure 3, you could not put the instruction to display the net pay before the instruction to calculate the net pay, and then expect the computer to display the correct results. When writing programs in a procedure-oriented language, the programmer must determine not only the proper instructions to give the computer, but the correct sequence of those instructions as well. Procedure-oriented high-level languages are a vast improvement over machine and assembly languages. Some of the procedure-oriented high-level languages for example, the BASIC language do not require a great amount of technical expertise to write simple programs. The Introduction of Windows As you know, Windows software provides an easy-to-use graphical user interface, referred to as a GUI, with which a user can interact. This GUI is common to all applications written for the Windows environment. It is this standard interface that makes Windows applications so popular: once you learn one Windows application, it is very easy to learn another. Although the standard interface found in all Windows applications makes the user s life much easier, it complicates the programmer s life a great deal. In the beginning, writing programs for the Windows environment was extremely tedious. Programmers found themselves spending countless hours writing instructions to create the buttons, scroll bars, dialog boxes, and menus needed in all Windows applications. Because the programmer has no control over which button the user will click in a Windows application, or which scroll bar the user will employ, the first Windows programmers had to write instructions that could handle any combination of actions the user might take. Tasks that used to take a few lines of program code now needed pages. Because programming Windows applications required a great amount of expertise, it appeared that the beginning of the Windows environment meant the end of the do-it-yourself, nonprofessional programmer. But then a new category of high-level languages emerged the object-oriented/event-driven high-level programming languages. Object-Oriented/Event-Driven High-Level Languages The object-oriented/event-driven high-level languages simplified the task of programming applications for Windows. In object-oriented/event-driven languages, the emphasis of a program is on the objects included in the user interface (such as scroll bars and buttons) and the events (such as scrolling and clicking) that occur when those objects are used. Unlike the procedure-oriented method of programming, the object-oriented method allows the programmer to use familiar objects to solve problems. The ability to use objects that model things found in the real world makes problem solving much easier. For example, assume that the manager of a flower shop asks you to create a program that keeps track of the shop s daily sales revenue. Thinking in terms of the objects used to represent revenue cash, checks, credit card receipts, and so on makes the sales revenue problem easier to solve. Additionally, because each object is viewed as an independent unit, an object can be used in more than one program, usually with little or no modification. A check object used in the sales revenue program, for example, also can be used in a payroll program (which issues checks to employees) and an accounts payable program (which issues checks to creditors). The ability to use an object for more than one purpose saves

5 An Overview of Visual Basic.NET overview VB 5 programming time and money an advantage that contributes to the popularity of object-oriented programming. Visual Basic.NET is an object-oriented/event-driven programming language that is easy enough for a nonprogrammer to use, yet sophisticated enough to be used by professional programmers. (Visual C++, C#.NET, Java, and Smalltalk also are object-oriented/event-driven programming languages.) With Visual Basic.NET it takes just a few clicks of the mouse to include standard Windows objects such as buttons, list boxes, scroll bars, and icons in your Windows application. You also can use Visual Basic.NET to create your own objects, such as the check object mentioned in the previous paragraph. Once the objects are created, the programmer then concentrates on writing the specific instructions telling each object how to respond when clicked, double-clicked, scrolled, and so on. For example, Figure 4 shows the Visual Basic.NET instructions that direct an object to close the application when the user clicks the object. (In this case the object is an Exit button.) Figure 4: A segment of a program written in Visual Basic.NET an object-oriented/eventdriven language Before running a sample object-oriented/event-driven application, you learn about the terminology used by object-oriented programmers. OOP Terminology Although you may have either heard or read that object-oriented languages are difficult to learn, do not be intimidated. Admittedly, creating object-oriented programs does take some practice. However, you already are familiar with many of the concepts upon which object-oriented programming is based. Much of the anxiety of object-oriented programming stems from the terminology used when discussing it. Many of the terms are unfamiliar, because they typically are not used in everyday conversations. This section will help to familiarize you with the terms used in discussions about object-oriented programming. Do not be concerned if you do not understand everything right away; you will see further explanations and examples of these terms throughout this book. When discussing object-oriented programs, you will hear programmers use the terms OOP (pronounced like loop) and OOD (pronounced like mood). OOP is an acronym for object-oriented programming and simply means that you are using an object-oriented language to create a program that contains one or more objects. OOD, on the other hand, is an acronym for object-oriented design. Like top-down design, which is used to plan procedure-oriented programs, OOD also is a design methodology, but it is used to plan object-oriented programs. Unlike top-down design, which breaks up a problem into one or more tasks, OOD divides a problem into one or more objects.

6 VB 6 overview OOP Terminology tip In OOP, behaviors also are referred to as methods. tip The class itself is not an object; only an instance of the class is an object. tip The term encapsulate means to enclose in a capsule. In the context of OOP, the capsule is a class. An object is anything that can be seen, touched, or used; in other words, an object is nearly any thing. The objects used in an object-oriented program can take on many different forms. The menus, radio buttons, and buttons included in most Windows programs are objects. An object also can represent something encountered in real life such as a wristwatch, a car, a credit card receipt, and an employee. Every object has attributes and behaviors. The attributes are the characteristics that describe the object. When you tell someone that your wristwatch is a Farentino Model 35A, you are describing the watch (an object) in terms of some of its attributes in this case, its maker and model number. A watch also has many other attributes, such as a crown, dial, hour hand, minute hand, and movement. An object s behaviors, on the other hand, are the operations (actions) that the object is capable of performing. A watch, for example, can keep track of the time. Some watches also can keep track of the date. Still others can illuminate their dials when a button on the watch is pushed. You also will hear the term class in OOP discussions. A class is a pattern or blueprint used to create an object. Every object used in an object-oriented program comes from a class. A class contains or, in OOP terms, it encapsulates all of the attributes and behaviors that describe the object the class creates. The blueprint for the Farentino Model 35A watch, for example, encapsulates all of the watch s attributes and behaviors. Objects created from a class are referred to as instances of the class, and are said to be instantiated from the class. All Farentino Model 35A watches are instances of the Farentino Model 35A class. Abstraction is another term used in OOP discussions. Abstraction refers to the hiding of the internal details of an object from the user; hiding the internal details helps prevent the user from making inadvertent changes to the object. The internal mechanism of a watch, for example, is enclosed (hidden) in a case to protect the mechanism from damage. Attributes and behaviors that are not hidden are said to be exposed to the user. Exposed on a Farentino Model 35A watch are the crown used to set the hour and minute hands, and the button used to illuminate the dial. The idea behind abstraction is to expose to the user only those attributes and behaviors that are necessary to use the object, and to hide everything else. Another OOP term, inheritance, refers to the fact that you can create one class from another class. The new class, called the derived class, inherits the attributes and behaviors of the original class, called the base class. For example, the Farentino company might create a blueprint of the Model 35B watch from the blueprint of the Model 35A watch. The Model 35B blueprint (the derived class) will inherit all of the attributes and behaviors of the Model 35A blueprint (the base class), but it then can be modified to include an additional feature, such as an alarm. Finally, you also will hear the term polymorphism in OOP discussions. Polymorphism is the object-oriented feature that allows the same instruction to be carried out differently depending on the object. For example, you open a door, but you also open an envelope, a jar, and your eyes. You can set the time, date, and alarm on a Farentino watch. Although the meaning of the verbs open and set are different in each case, you can understand each instruction because the combination of the verb and the object makes the instruction clear. Figure 5 uses the wristwatch example to illustrate most of the OOP terms discussed in this section.

7 An Overview of Visual Basic.NET overview VB 7 Blueprint of a Farentino Model 35A base class A watch s attributes and behaviors are encapsulated into the blueprint. Some attributes and behaviors are hidden; some are exposed derived class inherits properties of base class Attributes (Data) Maker Model number Crown Dial Hour hand Minute hand Movement Blueprint of a Farentino Model 35B Attributes (Data) Farentino Model 35A attributes Alarm Behaviors Track time Track date Illuminate dial Behaviors Farentino Model 35A behaviors Ring alarm objects instances of a class Figure 5: Illustration of OOP terms In the next section, you run a Visual Basic.NET application that gives you a quick look at some of the objects you learn how to create in the following tutorials. A Visual Basic.NET Demonstration The Visual Basic.NET application you are about to run shows you only some of the objects you learn how to create in the tutorials. For now, it is not important for you to understand how these objects were created or why the objects perform the way they do. Those questions will be answered in the tutorials. To run the Visual Basic.NET application: 1 Click the Start button on the Windows taskbar, and then click Run on the Start menu to open the Run dialog box. Click the Browse button in the Run dialog box. The Browse dialog box opens. 2 Locate and then open the VBNET\Overview folder on your computer s hard disk. Click Month (Month.exe) in the list of filenames, and then click the Open button. The Browse dialog box closes and the Run dialog box appears again. Click the OK button. After a few moments, Visual Basic.NET displays the Monthly Payment Calculator application shown in Figure 6.

8 VB 8 overview A Visual Basic Demonstration menu radio buttons text box list box labels button Figure 6: Monthly Payment Calculator application Figure 6 identifies some of the different objects appearing in the application s interface. Notice that the interface contains a text box, a list box, a button, radio buttons, labels, and a menu. You can use this application to calculate the monthly payment for a car loan. For example, determine the monthly payment for a $30,000 loan at 8% interest for five years. To compute the monthly car payment: 1 Type in the Principal text box, and then click 8.00 in the Interest % list box. The radio button corresponding to the five-year term is already selected, so you just need to click the Calculate button to compute the monthly payment. The Monthly Payment Calculator application indicates that your monthly payment would be $608.29, as shown in Figure 7. Figure 7: Computed monthly payment.

9 An Overview of Visual Basic.NET overview VB 9 Now determine what your monthly payment would be if you borrowed $10,000 at 7.25% interest for four years. 2 Type in the Principal text box. 3 Scroll up the Interest % list box until the 7.25 rate is visible, and then click Click the 4 years radio button, and then click the Calculate button to compute the monthly payment. The Monthly Payment Calculator application computes and displays the monthly payment of $ Notice that the application s menu bar has two menus: File and Color. View the options on both menus. To view the options on the Color and File menus: 1 Click Color on the menu bar. The Color menu opens and displays two options: Background and Information Box. You use the Background option to change the background color of the application s interface. 2 Click Background. The Color dialog box opens. Click a color of your choice, and then click the OK button. The color of the application s background changes accordingly. If you don t like the current color, you can use the Background option on the Color menu to select a different color. Now see what the Information Box option on the Color menu does. 3 Click Color on the menu bar, and then click Information Box. The Color dialog box opens. Click a color of your choice, and then click the OK button. The color of the information box changes accordingly. (The information box is the box in which you enter the principal, interest, and term information.) If you don t like the current color, you can use the Information Box option on the Color menu to select a different color. Now view the option on the File menu. 4 Click File on the menu bar. The File menu opens and shows one option: Exit. You can use the Exit option to end the Monthly Payment Calculator application. 5 Click Exit to close the Monthly Payment Calculator application. As you can see, programming languages have come a long way since the first machine languages. This brief history and demonstration should give you a better appreciation for the Visual Basic.NET programming language. Using the Tutorials Effectively The tutorials in this book will help you learn about Microsoft Visual Basic.NET, the newest version of the Visual Basic programming language. The tutorials are designed to be used at your computer. Begin by reading the text that explains the concepts. Then when you come to the numbered steps, follow the steps on your computer. Read each step carefully and completely before you try it.

10 VB 10 overview Questions As you work, compare your screen with the figures to verify your results. Don t worry if your screen display differs slightly from the figures. The important parts of the screen display are labeled in each figure. Just be sure you have these parts on your screen. Important note: Many of the figures in this book reflect how your screen will look if you are using a Microsoft Windows 2000 system. Your screen will look similar to these figures if you are using a Microsoft Windows XP system. Do not worry about making mistakes; that s part of the learning process. Help? notes identify common problems and explain how to get back on track. You should complete the steps in the Help? notes only if you are having the problem described. Tip notes provide additional information about a procedure for example, an alternative method of performing the procedure. Each tutorial is divided into three lessons. You might want to take a break between lessons. Following each lesson is a Summary section that lists the important elements of the lesson. After the Summary section are questions and exercises designed to review and reinforce that lesson s concepts. You should complete all of the end-of-lesson questions and exercises before going on to the next lesson. You cannot learn Visual Basic.NET without a lot of practice, and future tutorials assume that you have mastered the information found in the previous tutorials. Some of the end-of-lesson exercises are Discovery exercises, which allow you to both discover the solutions to problems on your own and experiment with material that is not covered in the tutorial. In each tutorial you will find one or more Debugging exercises. In programming, the term debugging refers to the process of finding and fixing any errors in a program. Debugging exercises provide debugging tips and allow you to practice debugging applications. Throughout the book you will find GUI (Graphical User Interface) design tips. These tips contain guidelines and recommendations for designing applications. You should follow these guidelines and recommendations so that your applications follow the Windows standard. Before you begin the tutorials, you should know how to use Microsoft Windows 2000 or Microsoft Windows XP. This book assumes you have learned basic Windows-navigation and file-management skills from Course Technology s New Perspectives on Microsoft Windows 2000 Brief, New Perspectives on Microsoft Windows XP Brief, or an equivalent book. Q U E S T I O N S 1. The set of directions given to a computer is called. a. computerese b. commands c. instructions d. a program e. rules 2. Instructions written in 0s and 1s are called. a. assembly language b. booleans c. computerese d. machine code e. mnemonics

11 An Overview of Visual Basic.NET overview VB languages allow the programmer to use mnemonics, which are alphabetic abbreviations for instructions. a. Assembly b. High-level c. Machine d. Object e. Procedure 4. languages allow the programmer to use instructions that more closely resemble the English language. a. Assembly b. High-level c. Machine d. Object e. Procedure 5. A(n) translates high-level instructions into machine code, line by line, as the program is running. a. assembler b. compiler c. interpreter d. program e. translator 6. A(n) translates the entire high-level program into machine code before running the program. a. assembler b. compiler c. interpreter d. program e. translator 7. A(n) converts assembly instructions into machine code. a. assembler b. compiler c. interpreter d. program e. translator 8. Visual Basic.NET is a(n) language. a. assembler b. machine c. mnemonic d. object-oriented/event-driven e. procedure-oriented 9. In procedure-oriented languages, the emphasis of a program is on how to accomplish a task. a. True b. False 10. In object-oriented languages, the emphasis of a program is on the objects included in the user interface and the events that occur on those objects. a. True b. False

12 VB 12 overview Questions 11. A(n) is a pattern or blueprint. a. attribute b. behavior c. class d. instance e. object 12. Which of the following is not an attribute that can be used to describe a human being? a. brown eyes b. female c. red hair d. talk e. thin 13. The object that you create from a class is called a(n). a. abstraction b. attribute c. instance d. procedure e. subclass 14. In the context of OOP, the combining of an object s attributes and behaviors into one package is called. a. abstraction b. combining c. encapsulation d. exposition e. inheritance 15. In the context of OOP, the hiding of the internal details of an object from the user is called. a. abstraction b. combining c. encapsulation d. exposition e. inheritance 16. Alcon Toys manufactures several versions of a basic doll. Assume that the basic doll is called Model A and the versions are called Models B, C, and D. In the context of OOP, the Model A doll is called the class; the other dolls are called the class. a. base, derived b. base, inherited c. derived, base d. exposed, hidden e. inherited, derived 17. In the context of OOP, refers to the fact that you can create one class from another class. a. abstraction b. combining c. encapsulation d. exposition e. inheritance

13 An Overview of Visual Basic.NET overview VB Use Figure 8 to answer the following questions Figure 8. a. What are the attributes (data or properties) associated with a dog class? b. What are the behaviors associated with a dog class? c. How many instances (objects) of the dog class are shown in Figure 8?