Software Development 2

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1 Software Development 2 Course Map This module introduces some of the techniques programmers use to create applications and programs. Introduction Computer Principles and Components Software Development Language Rules and Constructs The Java Language Rules and Tools Simple Java Programming Constructs Advanced Java Programming Constructs Objects, Arrays, and Methods Object Orientation Methods Arrays Advanced Object Orientation 2-1

2 Relevance Present the following questions to stimulate the students and get them thinking about the issues and topics presented in this module. They are not expected to know the answers to these questions. The answers to these questions should be of interest to the students, and inspire them to learn the content presented in this module. Discussion It is worthwhile at this point to ask yourself the following questions: How does a programmer design and develop programs? What are typical issues that programmers face when developing programs? What other problems can programming languages solve? How does a programming language actually work? Why are programmers so enthusiastic about the innovation that the Java programming language offers? What makes Java a superior programming language? How programs are developed? Note Programming is a difficult skill to master. It is not realistic to expect to become a competent programmer in just a few days. Much practice is necessary during and after you have completed this course. Emphasize this point! Students do attend expecting to leave as programming experts. 2-2 Java Programming for Non-Programmers

3 Objectives Upon completion of this module, you should be able to: State at least two different programming styles or paradigms Identify the major steps in the software development lifecycle Compare top down software design with bottom up software design Use a simple, common-sense design approach for object-oriented programs Given a simple Java program, identify the main components of the program Compare and contrast the layouts for a procedural and an objectoriented Java program Software Development 2-3

4 Programming Paradigms Definition In Module 1 you saw that compilers are required to convert your source code text files into the machine code that a computer can understand. You also saw that there are different generations of programming language which have been developed to make the programmer s job easier but sometimes at the expense of speed. Programming languages are also split across other groups, those formed by the language generations. These groups concern the paradigm that the language conforms to. The word paradigm means the way in which things happen and are allowed to happen in a context or world. For example, cartoons exist outside of the real world. Things that happen in cartoons would be impossible in the real world. The cartoon world is an alternative paradigm to our own. 2-4 Java Programming for Non-Programmers

5 Programming Paradigms Definition (Continued) Examples of programming paradigms include procedural, object oriented, and logical. The two most important are: Procedural In this paradigm the program is split into independent functions which all have access to common data elements. This is the most common paradigm. C and FORTRAN are procedural languages. Object Orientation (OO) In this paradigm the data is considered to be the most important part of the program. Instead of grouping the functions on the basis of what they do, the data is grouped into objects first and then the methods added appropriately. OO functions are only permitted to work on data within the local object. Java is an object-oriented programming language. The next section outlines the properties of the OO paradigm in more detail. Software Development 2-5

6 Programming Paradigms Object Orientation Imagine walking around a city and deciding you would like a coffee, so you look around and find a cafe. When you enter you do not walk behind the counter and make the coffee for yourself, you sit and ask the waitress who approaches you to prepare your drinks for you. You recognized the cafe as somewhere you could get a coffee. You do not know the manager or the waitress and may never even have been to the city before. When you recognized the cafe you knew you would be able to buy a drink there. This is an object-oriented way of thinking. Each object such as the cafe or the waitress has characteristics that make it recognizable, despite the distinguishing marks that also make it unique. It is just one instance of the group or class of objects called Cafe. 2-6 Java Programming for Non-Programmers

7 Programming Paradigms Object Orientation (Continued) OO source code files contain classes, the templates that will be used to build objects. At runtime the program builds enough objects from each class to solve a particular version of the problem. Objects have to be able to store the information that makes them unique. Variable declarations are placed inside the class definitions. When objects are built from the class they each get a different copy of those variables. Objects also need to perform operations on their attributes. Methods (functions) which are declared within the class definitions are also associated with each object of that class. Consider a class representing a bank account. It would require variables for transaction details, current balance, overdraft limit, interest rate, and so on. It would also require methods to pay money into the account, withdraw money, print statements, print balances, access personal information, and so on each task expected or required of an account would be represented as a method of that class. At runtime the Account class could be used to build separate Account objects for each of the bank accounts in your program. Each would be discrete and separate from the others, sharing a description and definition but not attributes. Emphasize the role of methods. Most people grasp the reason for classes, objects and variables, but think procedurally when considering the methods... stress their importance using an example (such as the account above). Use this opportunity to introduce concepts such as private and encapsulation as well. Again, it emphasizes the role of the method. But assess the readiness of the group first. Software Development 2-7

8 Product Development When you develop programs you must consider the requirements of your customer. You will always be writing the program for someone, even if that person is yourself, and unless the software does what your customer wants it to do, it will not be acceptable. There are many ways of managing the Software Development Lifecycle so that customers feel involved throughout the process and are constantly agreeing that you are producing exactly what they want. 2-8 Java Programming for Non-Programmers

9 Product Development Methodologies are all very similar to each other, generally implementing the following steps: 1. Requirements Gathering and Analysis 2. System Design 3. Construction/Implementation 4. Testing 5. Customer/User Testing 6. Maintenance One methodology that produces the quickest response (either positive or negative) from the customer is rapid prototyping or RAD (rapid application development). This involves very quickly producing a version of the product that looks and feels as much like the final version as is possible, but which obviously does not have all the functionality. The user can study the results and actually show you where it is wrong or needs adding. It will also identify to the customer those areas of the specification that were wrong or ambiguous. Rapid prototyping is especially well suited to the development of OO products because each part of a product will consist of one or more objects. It is not mandatory to have all the objects there simply to show the customer the RAD version. The Java programming language in particular allows for a very quick development of graphical user interfaces (GUIs), even without the aid of a GUI development tool. Software Development 2-9

10 Software Development Top Down and Bottom up Techniques The previous section outlines the need for product development methodologies. It is still necessary to use structured techniques within the product development cycle, however, especially at the software development stages. Many of the techniques that have been developed over the years are useful only within a particular programming paradigm. Two of the simplest techniques that can be applied to any paradigm are top down and bottom up. Top down Start by thinking of the overall problem and attempt to break it down into smaller sections. Then consider each of these in the same way until you have a hierarchy of all the components of your problem and how they interact Java Programming for Non-Programmers

11 Software Development Top Down and Bottom up Techniques (Continued) Bottom up Start by thinking of all the smallest components that you know will be required to solve the problem. Group them into larger components until you have a single solution to the problem. These methods are informal and flexible enough to permit their use only when and where appropriate. Designing OO software is made easier if you use a combination of them both, a technique that will be referred to as meet in the middle. Software Development 2-11

12 Software Development Meet in the Middle In the OO paradigm you have to analyze and design three types of components in a system: Classes The highest level building blocks of the solution, made up of: Attributes The small values that together make up a class. Operations The functions that operate on the class. Now consider the design of a Car object. Using a top down approach you could create a list containing Car, then Door, Engine, Wheel, Seats, and so on. Using a bottom up approach you might list numberofwheels, typeofseat, enginecapacity, turnleft, turnright, brake, accelerate and so on Java Programming for Non-Programmers

13 Software Development Meet in the Middle (Continued) The top down list specifies objects, so you must now write classes to define each of them. But what attributes are you interested in for each one? The bottom up list contains the attributes and methods for the system. Now you have to associate elements of the second list with items from the first to create complete class definitions. Any remaining classes without attributes or any methods and attributes not assigned to a class suggest errors or omissions in the design. Software Development 2-13

14 Primary Components of a Java Program Because Java is an object-oriented programming language the primary components of a program are: Objects Objects are instances of classes, which are defined in Java source code files. Objects contain variables and methods that are declared inside the class definitions. Attributes Variables placed inside the class definitions make the attributes of the objects. These can either be simple variables called primitives (such as numbers and characters) or references to other objects. Methods Objects contain their functionality as well as their attributes. Methods are functions that can be applied to the data within an object. There should be sufficient methods for each operation an object is expected to perform Java Programming for Non-Programmers

15 Primary Components of a Java Program When you design a class you add attributes which adequately and accurately model those objects within your application. Returning to the cafe example from a previous section, the Cafe class would probably contain text strings for the name, address, phone number, and so on, of the cafe and the number of tables it has, as well as the number of people currently in the cafe, and a list of the different drinks and dishes you can buy there. It would not be important to model the color of the walls or the number of windows, unless you were interested in such things. The content of a class depends on the problem you are solving and any preferences of your own you wish to add. Software Development 2-15

16 Group Exercise Discussion Use the meet in the middle methodology to analyze the objects and primary attributes and methods for a reasonably simple everyday task. It is not important to completely define each class. Then use the classes to outline the steps you would take to perform the task. Suggested tasks include: Making a cup of tea or coffee Making a sandwich Wrapping a gift Changing a car wheel Making your instructor walk across the room, considering his or her body to comprise several necessary but discrete objects (arms, legs, and so on). This exercise is intended to show students a little more clearly how the MITM technique can be used in real life, and how complex a seemingly simple task can be. Keep the discussion flowing freely. Allow the group to make some assumptions about there being a tap for water, that the kettle works, and so on, but stress the assumptions are to keep the exercise as simple as possible. They must realize the complexity of it all. At the end of the exercise you should have a white-board listing a sequence of statements developed by the group. Use this list to emphasize that a program (even an OO one) is basically a sequence of statements processed in order. Also emphasize that the two most basic programming tools are decisions (do I want milk or cream, do I want sugar, and so on) and loops to repeat certain steps (adding 0, 1, 2 or more sugars, loosening all the nuts on the wheel, or whatever). Also take the opportunity to show where similar or repeated (but not looped) statements could be re-written as methods to save time and processing. The students should finish this exercise knowing that in a very basic way programming skills are very simple (statements, sequences, decisions and loops, with methods to help) and that they will learn all of these skills before the end of the course Java Programming for Non-Programmers

17 Procedural and OO Programs It is possible to write procedural programs as well as OO ones in the Java programming language. An OO program uses objects to store and manipulate values while a procedural one stores them locally in the functions themselves. The following sections introduce the minimum Java application in both procedural and OO form. The minimum application will print a message on the screen. Software Development 2-17

18 Procedural and OO Programs A Minimum Procedural Java Program 1 class MinProcApp 2 { 3 public static void main (String args[]) 4 { 5 System.out.println("My first program"); 6 } 7 } Line 1 declares a class called MinProcApp. class is keyword; all keywords are lower case. MinProcApp is the name of the class. Lines 2 and 7 have braces to mark the beginning and end of the class. Line 3 declares a method called main. The whole of this line is mandatory the keywords public, static and void will be explained later. All Java applications have a main method declared exactly in this way. It is the starting point of the program, the first method that will be called. Lines 4 and 6 have braces to mark the beginning and end of the main method. Line 5 prints the message "My first program". All the work takes place in the main method, which is the way many procedural programs work Java Programming for Non-Programmers

19 Procedural and OO Programs A Minimum OO Java Program 1 class MinOOApp 2 { 3 public static void main (String args[]) 4 { 5 ObjectOne one = new ObjectOne(); 6 one.go(); 7 } 8 } 9 10 class ObjectOne 11 { 12 public void go() 13 { 14 System.out.println("My first OO program"); 15 } 16 } Lines 1, 2 and 8 are the declaration and braces for a class called MinOOApp. Lines 3, 4 and 7 are the declaration and braces of the main method, exactly as in the minimum procedural application. Line 5 creates an instance of the other class ObjectOne. The syntax of this line will be explained in a later module. Line 6 invokes the go method of the object via its reference one. Lines 10, 11 and 16 are the declaration and braces for another class, called ObjectOne. Lines 12, 13 and 15 are the declaration and braces for a method called go. Line 14 prints out the message. Software Development 2-19

20 Exercise: Creating the Minimum Example Programs Exercise objective The objective of this exercise is to create Java source files for the programs presented in this module, and then compile and run them. Tasks 1. Change directory to the MyApps directory. 2. Create a subdirectory called MinApps. 3. Change directory to the new MinApps directory. 4. Type both the minimum programs into text files in that directory. Call the first file MinProcApp.java. Call the second file MinOOApp.java. 5. Compile and run both programs. To compile a file use the command: javac filename.java where filename is either MinProcApp or MinOOApp, as appropriate. To run the program, type the command: java classname where classname is the name of the class that contains the main method Java Programming for Non-Programmers

21 Exercise: Creating the Minimum Example Programs Exercise Summary Discussion Take a few minutes to discuss what experiences, issues, or discoveries you had during the lab exercises. Manage the discussion here based on the time allowed for this module, which was given in the About This Course module. If you find you do not have time to spend on discussion, then just highlight the key concepts students should have learned from the lab exercise. Experiences Ask students what their overall experiences with this exercise have been. You may want to go over any trouble spots or especially confusing areas at this time. Interpretations Ask students to interpret what they observed during any aspects of this exercise. Conclusions Have students articulate any conclusions they reached as a result of this exercise experience. Applications Explore with students how they might apply what they learned in this exercise to situations at their work place. Software Development 2-21

22 Check Your Progress Before continuing on to the next module, check that you are able to accomplish or answer the following: State at least two different programming styles or paradigms Identify the major steps in the software development lifecycle Compare top down software design with bottom up software design Use a simple, common-sense design approach for object-oriented programs Given a simple Java program, identify the main components of the program Compare and contrast the layouts for a procedural and an objectoriented Java program 2-22 Java Programming for Non-Programmers

23 Think Beyond Now that you are familiar with several approaches to software design, what are the rules, syntax, and constructs for writing programs in the Java programming language? Software Development 2-23

24 2-24 Java Programming for Non-Programmers

Computer Principles and Components 1

Computer Principles and Components 1 Course Map This module provides an overview of the hardware and software environment being used throughout the course. Introduction Computer Principles and Components