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Appendix H: Procedural Code in Java The FOREACH

webmaster — Wed, 08 Jul 2009 14:11:47 +0000

Appendix H: Procedural Code in Java The FOREACH clause introduces acc as a reference to one of the Account objects in the collection theAccounts. Within the FOREACH loop we use acc to represent the next Account object we are processing. We can also use a variant of the FOREACH pseudo-code to indicate repetition a set number of occasions. We might, for example, use a FOREACH to show how the sum of the first ten input values is achieved: initialize the total to zero FOREACH num IN 0..9 DO prompt user for the next input value read the value add the value to the total ENDFOREACH Of course, the Java for this is: double total = 0.0; for(int num = 0; num<10; num++) { ConsoleIO.out.print( Please enter next value: ); double value = ConsoleIO.in.readDouble(); total += value; }

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Appendix H: Procedural Code in Java WHILE selection

webmaster — Tue, 07 Jul 2009 13:38:39 +0000

Appendix H: Procedural Code in Java WHILE selection is not choice number 0 DO IF selection is choice number 1 THEN provide service for choice number 1 ELSE IF selection is choice number 2 THEN provide service for choice number 2 ELSE IF … THEN … ENDIF present the menu to the user read the selection made by the user ENDWHILE Again, this maps directly into Java as shown below. Note how presenting the menu and obtaining the user s selection is relegated to a support method called getSelection. The Structured English described by the WHILE and IF have direct counterparts in Java. String choice = this.getSelection(); while(choice.equals( 0 ) == false) { if(choice.equals( 1 )) { // Get the borrower details from the human user ConsoleIO.out.print( t + Enter the borrower name >>> ); String borrowerName = ConsoleIO.in.readString(); // Register the borrower with the Library library.registerOneBorrower(borrowerName); } else if( choice.equals( 2 ) == true) { // … } // … else { ConsoleIO.out.println( ntt + Unknown selection - try again + n ); } choice = this.getSelection(); } Alternatively, we might have considered a do loop and nested if-else statement: String choice = ; do { // Get the human user s choice. choice = this.getSelection(); ConsoleIO.out.println(); // // Action the human user s choice. if(choice.equals( 0 )) { ConsoleIO.out.println( ntt + SYSTEM CLOSING + n ); ConsoleIO.out.println(); }

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Object-Oriented Design with UML and Java Observe how

webmaster — Tue, 07 Jul 2009 02:40:12 +0000

Object-Oriented Design with UML and Java Observe how program code is totally absent. This is intentional, we simply wish to convey the actions required in getting some input from the user. If we then subsequently add some detail, then the following Java emerges: ConsoleIO.out.print( Please enter date as DD MM YYYY: ); int day = ConsoleIO.in.readInt(); int month = ConsoleIO.in.readInt(); int year = ConsoleIO.in.readInt(); The following pseudo-code presents some logic in which the user is prompted to provide a date that is then validated and an appropriate message displayed. prompt the user for a date read the date from the user IF the date is valid THEN display date is valid ELSE display date is invalid ENDIF Observe how the italicized text simply describes what should occur without detailing how it should be implemented. In particular note the phrase the date is valid, which seeks to determine if we have a valid date. No attempt is made to describe how this will be done. In fact, further pseudo-code can be introduced to outline the required logic for this as a separate activity. Note also structured logic described by the IF THEN ELSE ENDIF control structure. This part of the pseudo-code identifies the need for a two-way selection to determine the output to be produced. The THEN and ELSE indicate choice, while IF and ENDIF delimit the extent of the selection. The pseudo-code is readily translated into its Java implementation. Ignoring how the date is validated, and using the textio package from appendix C, we arrive at: ConsoleIO.out.print( Please enter date as DD MM YYYY: ); int day = ConsoleIO.in.readInt(); int month = ConsoleIO.in.readInt(); int year = ConsoleIO.in.readInt(); if(…) ConsoleIO.out.println( date is valid ); else ConsoleIO.out.println( date is invalid ); Iteration 2 of the case study from chapter 4 introduces a simple menu into the text- based user interface. The menu operates by first prompting the user with a set of numbered choices. The user selects from this list and the necessary service is provided. The menu is repeated and the process continues until the user selects numbered choice 0 to exit the system. The pseudo-code that would have first described this logic is given as: present the menu to the user read the selection made by the user

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Appendix H Procedural Code in Java Appendix D

webmaster — Mon, 06 Jul 2009 14:17:16 +0000

Appendix H Procedural Code in Java Appendix D is primarily concerned with the mappings from the elements of a class diagram to Java classes. They were simply concerned with the major constructs including interfaces, classes, relations, class attributes and methods. In this appendix we examine the procedural code of class methods. In addition, we outline the pseudo-code that we use to describe program logic. H.1 Procedural code Java s procedural code is used to implement a method body. This code can also appear in initialization blocks as described in chapter 7. Procedural code is assembled from the three control structures of sequence, selection and iteration (repetition). These three control structures are prepared in any combination to describe the logic required. In Java the if and switch statements represent the language s two selection statements. The while, do and for are the repetition statements. Combining these structures in any manner means that an if statement can be nested within another if statement, or a while statement can be used in an if statement, and so on. As we form complex control logic then it too will benefit from the application of some design. This we achieve by developing pseudo-code to describe the intended logic before converting it into actual Java statements. Pseudo-code, as its name suggests, is not Java code but bears some passing resemblance to it. Pseudo-code aims to describe the intention of some logic by using code-like constructs. Pseudo-code is sometimes also known as a Program Design Language (PDL) or by the term Structured English, in which some restricted form of natural language is used to describe our intent. The language used with pseudo-code is a mix of fixed constructs and paraphrased statements. The idea of fixed constructions is evident from the name Structured English. Some parts of the language used are constrained to some fixed structures. The remainder of the pseudo-code is composed of short phrases that describe the intent. We distinguish the latter by using italic font. The fixed structures are presented as emboldened text. A simple illustration of pseudo-code with no structured elements is given below. It simply identifies that we need to obtain a date from the user and that we prompt the user when it is required. It represents an example of sequential code. prompt the user for a date read the date from the user 393

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This Page Intentionally Left Blank

webmaster — Mon, 06 Jul 2009 02:38:07 +0000

This Page Intentionally Left Blank

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Appendix G: Object-Oriented Programming with Java 6. How

webmaster — Sun, 05 Jul 2009 15:09:02 +0000

Appendix G: Object-Oriented Programming with Java 6. How is a redefined method introduced into a Java subclass? 7. The Java keyword abstract has two uses. Give examples of each and explain their usage. 8. Answer the following, giving explanations. (a) Can an interface extend another interface? (b) Can an interface extend more than one interface? (c) Can an interface subclass an abstract class? (d) Can an abstract class extend another abstract class? (e) Can a concrete class extend an interface? (f) Can a concrete class implement an interface? (g) Can a concrete class implement two interfaces and extend an abstract class? (h) Can a concrete class extend two abstract classes? 9. Develop a Person class with name and age properties. Now develop two specializations from class Person. Prepare the class Student as a subclass of Person with a matriculation number attribute. Revise the Employee class from this chapter with Person as its superclass. 10. Develop the class Employee with name and employee number attributes. Provide suitable methods for this class. Introduce into the class the abstract operation computeMonthlyPay that is redefined in the subclasses SalariedEmployee and HourlyEmployee. A salaried employee has a salary, which is paid out monthly. An hourly employee has a fixed pay rate and a number of hours worked per month. Implement the method computeMonthlyPay for these two subclasses. 11. Develop a class Account having a balance and account number attributes. Introduce the methods debit and credit that implement deposit and withdrawal transactions on a bank account. Form two specializations for the classes DepositAccount and CurrentAccount. A deposit account accrues interest and cannot be overdrawn while a current account may be overdrawn up to some overdraft limit. 12. Develop the concrete class Circle as a subclass of ClosedFigure. Test its behaviour using program G.4. 13. Develop the class Quadrilateral to represent any four-sided figure, then specialize this into the subclasses Rectangle and Square. Choose a suitable representation for the Quadrilateral and implement the operations getPerimeter and getArea. Redefine both these for the two subclasses. 14. Look up the Swing class Jframe in the Java documentation and present its super- class hierarchy. 15. Look up the Swing classes WindowListener and WindowAdapter in the Java documentation files. What is the class hierarchy of these two classes? Why is class WindowListener an interface? How is class WindowAdapter a concrete class?

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Object-Oriented Design with UML and Java public Rectangle(double

webmaster — Sun, 05 Jul 2009 05:07:52 +0000

Object-Oriented Design with UML and Java public Rectangle(double upperLeftX, double upperLeftY, double width, double height) { this(new Point(upperLeftX, upperLeftY), width, height); } public double getPerimeter() { return 2 * (theWidth + theHeight); } public double getArea() { return theWidth * theHeight; } // —– Attributes —————-private Point theUpperLeft; private double theWidth; private double theHeight; } The sample application code is given in program G.4. Here, we create instances of the Rectangle and Triangle classes and interrogate each for their perimeter and area values. Program G.4 public class Main { public static void main(String[ ] args) { Rectangle rect = new Rectangle(0.0, 4.0, 4.0, 4.0); // square 4 x 4 Triangle tri = new Triangle(0.0, 0.0, 3.0, 0.0, 3.0, 4.0); // 3-4-5 right triangle ConsoleIO.out.println( Rectangle: + rect.getPerimeter() + , +rect.getArea()); ConsoleIO.out.println( Triangle: + tri.getPerimeter() + , +tri.getArea()); } } G.4 Exercises 1. Carefully distinguish between the terms interface, abstract class and concrete class. 2. Carefully distinguish between the Java keywords extends and implements, ensuring that you are clear where they are used. 3. Carefully distinguish between the terms superclass and subclass. How may a subclass differ from its superclass? How much commonality is there? Describe what is meant by substitutability when discussing superclass and subclass. 4. What do you understand by the terms redefinition and the polymorphic effect? Explain their value to OO development. 5. What feature does a subclass constructor method use to initialize inherited attributes?

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Appendix G: Object-Oriented Programming with Java Java supports

webmaster — Sat, 04 Jul 2009 18:08:24 +0000

Appendix G: Object-Oriented Programming with Java Java supports multiple inheritance through interfaces. A class can be an extension of at most one abstract class or concrete class and implement any number of interfaces. The isA relation is still present, but now an instance of the subclass can be substituted for any of the superclasses, including the interfaces. Consider any two-dimensional closed figure such as a rectangle or a triangle for which we wish to obtain the length of its perimeter or its area. The interface ClosedFigure introduces the protocols for obtaining these values, which every concrete subclass must implement. Further, we can develop code in terms of this interface without consideration for the actual type of closed figure with which we are interacting. That way, our code is made much more adaptable. interface ClosedFigure Operations +getArea +getPerimeter Rectangle Triangle Figure G.6 Specialization hierarchy Figure G.6 shows the class hierarchy we shall develop. The code for the interface ClosedFigure is: public interface ClosedFigure { public abstract double getPerimeter(); public abstract double getArea(); } The code for the two concrete subclasses must include implementations for these two deferred methods. Below is the code for the Rectangle class using a variant of the Point class (using doubles rather than ints). The Triangle class would be developed similarly. public class Rectangle implements ClosedFigure { public Rectangle(Point upperLeft, double width, double height) { theUpperLeft = upperLeft; theWidth = width; theHeight = height; }

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Object-Oriented Design with UML and Java co.hire(e1, m3);

webmaster — Sat, 04 Jul 2009 07:33:25 +0000

Object-Oriented Design with UML and Java co.hire(e1, m3); co.hire(e2, m3); co.printEmployeeDetails(); } } The UML collaboration diagram of figure G.5 shows the configuration of objects and the message flows between them. The application, represented by the actor, sends the message printEmployeeDetails to the Company object with identity co. This Company object then sends the message printDetails in turn to the three employee objects. When the message printDetails is received by the manager object it executes the redefined version for this method. The method printDetails from class SalesManager prints the managers details then gets the names of the two employees that are members of that manager s team. e1 : Sales Employee e2 : Sales Employee co : Company m3 : SalesManager 2: printDetails 4: printDetails 3: printDetails 1: printEmployee Details 2.2: getName 2.1: getName Figure G.5 Collaboration diagram G.3 Interfaces An interface is a particular kind of abstract class in which all methods are deferred and for which there are no (non static) attributes. In effect, an interface is a pure abstract class. A Java interface is implicitly public as are all its methods. Further, these methods are implicitly qualified as abstract. It is permissible in Java to make these qualifications explicit, rendering additional documentation for the reader. A Java interface is permitted to contain class attributes but these must be static and final. Java interfaces are sometimes used to collect a number of related constants. Other classes can then refer to them using the class name qualifier or by subclassing to provide direct referencing. Since an interface has no state we say that any specialized class implements an interface. An abstract class or a concrete class can implement an interface. A subclass that is itself another interface is said to extend the interface superclass.

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Appendix G: Object-Oriented Programming with Java public void

webmaster — Fri, 03 Jul 2009 20:29:07 +0000

Appendix G: Object-Oriented Programming with Java public void hire(SalesEmployee sales, SalesManager man) { Iterator iter = theEmployees.iterator(); while(iter.hasNext() == true) { Employee emp = (Employee)iter.next(); if(emp instanceof SalesManager && emp == man) { SalesManager manager = (SalesManager)emp; manager.addSalesMember(sales); } } theEmployees.add(sales); } public void printEmployeeDetails() { ConsoleIO.out.println( Company: +theName); Iterator iter = theEmployees.iterator(); while(iter.hasNext() == true) { Employee emp = (Employee)iter.next(); emp.printDetails(); } } // —– Attributes —————-private String theName; private ArrayList theEmployees = new ArrayList(10); } Finally, the application is shown in Program G.3. The program run produces the output shown below. The manager Jessie Kennedy presents both her details as well as listing the names of her sales team. The other employees simply list their details. Company: Napier Manager: Jessie Kennedy, Professor, 1200, Budget: 8000 Sales member: Ken Barclay Sales member: John Savage Sales employee: Ken Barclay, Lecturer, 1000, Sales target: 2000 Sales employee: John Savage, Lecturer, 1200, Sales target: 2000 Program G.3 public class Main { public static void main(String[ ] args) { SalesEmployee e1 = new SalesEmployee( Ken Barclay , Lecturer , 1000, 5000); SalesEmployee e2 = new SalesEmployee( John Savage , Senior Lecturer , 1200, 2000); SalesManager m3 = new SalesManager( Jessie Kennedy , Professor , 1200, 10000); Company co = new Company( Napier ); co.hire(m3);

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