The Final One. Case Study: Adding a GUI to the Student Data Base. Graphical Use Interfaces: the student database example. Assignments.

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1 The Final One Graphical Use Interfaces: the student database example. Assignments. Module questionnaire. Looking back Case Study: Adding a GUI to the Student Data Base Problem. We want to add a simple graphic interface to the system described in Lecture 14. Problem analysis. The user should be able to choose one of the four options list all students, find a code, find a name, and quit from a drop-down menu. The input to a search should be written in a text field and we assume it is available when the option in the menu is chosen. The results of a query are displayed in a textual area. Class analysis. There are few differences and few addition to the class diagram in Lecture 14. StudentDB main() StudentRecords NUMBER_OF_SUBJECTS positioninvector: int positiontosearch: int average (int index) searchid (int id) searchname (String name) displayallrecords() displaystudentrecord() Gui largestposition actionperformed(actionevent e) TextArea contains TextField ActionListener actionperformed(actionevent e) Record id: int name: String results: int[] MenuBar Menu addactionlistener(actionlistener l) add(menu m) contains 2 3

2 The classes shown in green are Java predefined classes and interfaces used to implement the graphical user interface (inheritance hierarchies are not shown). Gui is the class of the graphical user interface. It has a menu bar, a text field (for the input) and a text area for the output. The method actionperformed(actionevent e) encapsulates the interaction between the interface and the StudentRecords class. The interface will use the method e.getactioncommand() to get as a string the value of the selected option. The main class StudentDB does not need to know about the StudentRecords anymore! The interface encapsulates the knowledge of that class. The display methods in StudentRecords had to be modified: the I/O is not through readers and writers anymore. public String displaystudentrecord() { int s; StringBuffer buf; buf = buf.append(((record) recordstore.elementat(positioninvector)).id); buf = buf.append(((record) recordstore.elementat(positioninvector)).name + for ( s = 0; s < NUMBER_OF_SUBJECTS; s++) { buf = buf.append(((record) recordstore.elementat(positioninvector)).res buf = buf.append("\taverage "); buf = buf.append( average(positioninvector) ); buf = buf.append("\n"); return buf.tostring(); public String displayallrecords() { int i, s; StringBuffer buf = new StringBuffer(); for ( i = 0; i < recordstore.size(); i++) { buf = buf.append(((record) recordstore.elementat(i)).id); buf = buf.append(((record) recordstore.elementat(i)).name + "\t"); for ( s = 0; s < NUMBER_OF_SUBJECTS; s++) { buf = buf.append(((record) recordstore.elementat(i)).results[s]); buf = buf.append("\taverage "); buf = buf.append( average(i) ); buf = buf.append("\n"); return buf.tostring(); Algorithm for Gui s constructor 1. general settings (background color and layout) 2. menu definition (including setting up the action listener) 3. definition of the (output) text area 4. definition of the (input) text field 5. initialisation of the instance of StudentRecords 4-1 5

3 Algorithm for actionperformed(...) 1. if option is list 2. reset the output text area 3. set buf to the result of displayallrecords() 4. display the results 5. else if option is Search Id 6. reset the output text area 7. get id from the input text field 8. if searchid(id) 9. reset the output text area 10. set buf to the result of displaystudentrecord() 11. display the result... Let s have a look at the code! Assignment 6. This last assignment builds on your solution to Assignment 5. Your task is to define a class DeliveryPerson and implement it so that an object in this class can perform the wealth transfers requests accumulated in the file requests.txt (as described in Assignment 5). The final system will implement a very simple example of producer-consumer system, with the towns producing wealth transfer requests and the delivery person consuming the requests (by fulfilling them). The producer (the town map) and the consumer (the delivery person) interact asynchronously through the requests.txt file.... Let s look at the whole system in action. 6 8 Assignments! Read your , check the module web-page for news/marks. Assignment 5. Now that it is all done and sent ask yourself: The map evolves in a sequence of steps. During each step each town may decide to perform a wealth transfer. After step 20, say, this may be the situation. Am I able to define a Town class with a name and wealth attribute, define a constructor for it (initialising all attributes receiving input values from the user), and finally define a display method that prints to the screen the town s attributes? Am I able to define a Road class with two Town attributes and (as before) define a constructor for it (initialising all attributes receiving input values from the user), and finally define a display method that prints to the screen the roads attributes? If this is NOT the case, then DO NOT start working on Assignment 6, and solve these two exercises first (or come to see me next week if you need help). Step 20 Freepool Townsite Burgh Elsewhere Freepool Elsewhere 2 Townsite Burgh 3 Burgh Elsewhere

4 Delivery person (in previous step) has moved to Freepool and is busy. The Map Step 21 Freepool Elsewhere 2 Freepool Burgh Townsite Burgh 3 Burgh Elsewhere 1 Burgh Townside 1 Binary files for the classes Map, Town and Road can be downloaded from the course web-page. Here s a description of each class in turn. A town (class Town) provides the following services: // constructor public Town ( String s, int w, int l ) Townsite Elsewhere New requests generated during Step 21 // methods public String getname () public int getwealth () public int getlatest_request () public void setwealth ( int w ) public void setlatest_request ( int l ) The money transfer has now been performed. Delivery person is idle and looking for a new job. As far as this assignment is concerned a road (class Road) is just a connection between two towns: Step 22 Freepool Townsite Burgh Elsewhere Townsite Burgh 3 Burgh Elsewhere 1 Burgh Townside 1 Elsewhere Townside 3 Freepool Elsewhere 4 New requests generated during Step 22 // constructor: it returns a random road between two // towns from a list c of n towns. The random // number generator src is used to set up the road // distances (but this should be of no concern to you) public Road ( Town[] c, int n, Random src ) // return First (resp Second) end-point of the road public String getfirst () public String getsecond ()

5 Here comes the description of constructors and methods in the main class of the system (class Map). // constructor public Map ( int n, // number of towns int m, // number of roads double p, // request generation probability Random src // random number generator ) // returns the number of cities in the map public int getnumber_of_cities () // display some information about the map. If // printroads is true then additional information // about the roads in the map is printed; otherwise // only information about the Map s towns is shown. public void displaymap ( boolean printroads ) How do we use this? I have made the classes above into a package. You should: 1. Create, in the same directory where your Assignment 6 program will be, a directory called Map. 2. Download the class files for classes Town, Road, and Map in the subdirectory Map. 3. Type in the following little program (to check that everything is set up properly) // method for making the Map evolve. Each town is // given the opportunity to issue a transfer request. // Requests are logged in the file ff. public void evolve ( String ff, // name of the output file Random src // random number generator ) import java.io.*; import java.util.random; import Map.*; // <== Importing the Map related classes class Try { // returns the index of town s public int getindex ( String s ) // returns the Town of index i public Town gettown ( int i ) public static void main (String[] args) throws IOException { Random source = new Random(); Map M = new Map(0,0,1.0,source);

6 That s all Folks (Module aims) (a) To teach the students the elements of the Java programming language. (b) To give the students a general understanding of object-oriented programming, with respect to the analysis, design and implementation stages of program development. (From the module Learning Outcomes) (a) Fluency in the Java programming language. (b) An understanding of encapsulation and the benefits of software modularity. (c) The skills necessary to analyse a problem, produce an object- oriented design for a solution, then implement this in Java. What is a method? What is a parameter? Can you solve simple exercises involving classes? Do you think you are getting the grip of how different classes may interact with each other? What have you learnt? A lot! Do you understand what a data type is and what data types are available in Java? Are you familiar with Java classes like String or Math or BufferedReader? Do you think you know how to write a JAVA program involving assignments, selection statements or loops? Do you feel capable of solving (through a Java program) a problem involving search in an array or table? If you can answer positively to % of these questions I think this module has achieved its aims and you are prepared to learn more in the next semester. Programming is important. Programming is fun! It may be challenging, but it is ALWAYS rewarding, eventually