Assignment 4: Object creation

Transcription

1 Assignment 4: Object creation ETH Zurich Hand-out: 12 October 2007 Due: 19 October 2007 Copyright FarWorks, Inc. Gary Larson Goals Create objects in Traffic. Write a first stand-alone program. Create and use a new class. Learn about the basic input and output operations in Eiffel. Repeat the difference between strict and non-strict boolean operators. 1 Creating objects in Traffic Up to now you have always worked with existing, predefined objects of Paris. In this assignment you will create new objects and add them to Paris. To build new map objects in Traffic (be it passengers, trams, places, lines, roads, etc.) you can follow a general scheme: 1. Declare an attribute or local variable of the according type. This step is needed, so that the software knows that the identifier you will be using in the code is valid and what type of object it can denote. If you forget this step, the Eiffel compiler will produce an error saying that you are using an Unknown identifier. The declaration of a new attribute is always placed outside of other feature declarations, 1

2 but between the keyword feature (line 8 in Listing 1) and (line 21 in Listing 1) of the class text. It is composed of the identifier (name for the new object), a colon, and the type of it. In our example the identifier is place and the type is TRAFFIC PLACE. 2. Create the object using one of the creation procedures declared in the according class. If you forget this step, the declared identifier will be void and calling features on it will result in a program crash (displaying the message Feature call on Void target ). If you like you can set additional properties of the object. To detect the available creation procedures, look at the text of the class used in step 1. They are listed in the creation clause of the class header (see lines 17 and 18 of Listing 2). In our example a TRAFFIC PLACE can be created using either make or make with position as a creation procedure. make with position requires three arguments: a STRING object and two INTEGER objects. Note that for STRINGs there is a fast track to object creation: Just put the text you want in the STRING object between double quotation marks. For INTEGERs this fast track is done by writing the number at the appropriate position. 3. Add the object to the map by adding it to the according container. If you forget this step, there will be no compiler error and no program crash, but you won t see the object on the displayed map. The class TRAFFIC MAP provides several containers for the various types of map objects and for each there is a command that allows you to put a new object into the container. To make things easier, we list them here and show you for most map item types how they should be put into the according container: Example declaration Adding it to the map pl: TRAFFIC PLACE Paris.places.force (pl, pl.name) l: TRAFFIC LINE Paris.lines.force (l, l.name) r: TRAFFIC ROAD Paris.roads.force (r, r.id) pa: TRAFFIC PATH Paris.paths.put last (pa) bv: TRAFFIC VILLA Paris.buildings.put last (bv) ba: TRAFFIC APARTMENT BUILDING Paris.buildings.put last (ba) bl: TRAFFIC LANDMARK Paris.buildings.put last (bl) bs: TRAFFIC SKYSCRAPER Paris.buildings.put last (bs) te: TRAFFIC EVENT TAXI OFFICE Paris.taxi offices.put last (te) td: TRAFFIC DISPATCHER TAXI OFFICE Paris.taxi offices.put last (td) p: TRAFFIC PASSENGER Paris.passengers.put last (p) t: TRAFFIC TRAM Paris.trams.put last (t) b: TRAFFIC BUS Paris.busses.put last (b) f: TRAFFIC FREE MOVING Paris.free movings.put last (f) 1 class CREATION EXAMPLE 3 inherit 5 TOURISM 7 feature Explore Paris 9 explore on click is 11 Create a new place. do 13 Paris. display Listing 1: Creating a new TRAFFIC PLACE object 2

3 create place.make with position ( Home, 600, 700) Step 2: Creation of the new object 15 Paris.places. force (place, place.name) Step 3: Adding new object to the map 17 place : TRAFFIC PLACE Step 1: Declaration of attribute 19 New place 21 1 class TRAFFIC PLACE 3 inherit 5 HASHABLE redefine 7 out 9 TRAFFIC MAP ITEM 11 undefine out, 13 add to map, remove from map 15 Listing 2: Class TRAFFIC PLACE (shortened) 17 create make, make with position 19 feature {NONE} Initialize 21 make (a name: STRING) is 23 Initialize Current. require 25 a name exists: a name /= Void a name not empty: not a name.is empty 27 ensure name set: equal (a name, name) 29 position exists : position /= Void 31 make with position (a name: STRING; a x, a y: INTEGER) is 33 Initialize Current with name a name and position a x, a y. require 35 a name exists: a name /= Void a name not empty: not a name.is empty 37 ensure name set: equal (a name, name) 39 position exists : position /= Void position set : position.x = a x and position.y = a y feature Access 45 [... ] 47 To do 1. Before you start, please replace the file traffic/library/traffic line.e with the file provided at line.e, 3

4 and the file traffic/library/visualization/vision2/views/traffic vs view factory.e with the file provided at vs view factory.e. 2. Download 4.zip and extract it in traffic/example. You should now have a new directory traffic/example/ ev assignment 4 with assignment 4.ecf directly in it (it is important that the location corresponds to the description here!). 3. Open and compile this new project. Open class OBJECT CREATION and solve the tasks below in feature explore on click. 4. Create a new TRAFFIC PASSENGER that walks along Route1. Don t forget to call feature go on it (this will make it start moving). 5. Create four objects of type TRAFFIC TRAM. One should follow Line1, another Line2, yet another Line7 a, and the last one Line8. To make them start moving, call feature start on each of them. 6. Create four new TRAFFIC LANDMARKs with the following attributes and add them to the map: position image file (750, 700)../map/paris/notredame.png (120, 350)../map/paris/defense.png (800, 600)../map/paris/centrepompidou.png (300, 500)../map/paris/triomphe.png 7. For each of the landmarks, create a new TRAFFIC PLACE (plus additional places for the existing landmarks Louvre and Eiffel tower). Add them to the map and highlight them. Positions and names are given below: name position Notre Dame (750, 730) La Defense (120, 380) Centre Pompidou (800, 630) Arc de Triomphe (300, 540) Musee du Louvre (475, 650) Tour Eiffel (270, 840) 8. Create a new line of type TRAFFIC LINE. Make sure to use the creation procedure make with terminal, otherwise you will get a precondition violation when using the feature ext on it. The creation procedure has three arguments: the first one is the name of the new line, this should be Tourist line ; the second is the type of line, in our case this should be a bus line, so use an object of type TRAFFIC TYPE BUS as second argument; the third argument defines the starting place of the line, which in our case is the place with name La Defense (created in step 7). Use the feature ext to add the other five places created in step 7 as stops to the tourist line. 9. Create a new object of type TRAFFIC BUS that moves along the tourist bus line. To make the bus driving back and forth infinitely, call feature set reiterate (True) on the bus. To hand in Submit the class text of OBJECT CREATION to your assistant. 4

5 2 Temperature application In this task you will write an application which converts temperatures between Celsius, Fahrenheit, and Kelvin units. The application should consist of two classes: TEMPERATURE and TEMPERATURE APPLICATION. The latter is the root class. Things you need to know To print something in the console window, use io.put string, io.put integer, io.put boolean and so on, deping on the type of the argument. To read user input, use io.read... This places the read value in a buffer. Use io.last... to retrieve the value from the buffer. As an example, reading an INTEGER from the console and then displaying it on the screen, looks as follows: f is Read integer and display it. local i : INTEGER do io. read integer i := io. last integer io. put integer (i) The formulas for conversion: To do F ahrenheit = (9/5) Celsius + 32 Kelvin = Celsius Launch EiffelStudio. Create a new project of type Basic application (no graphics library included), using the settings shown in figure 1. Figure 1: New project 5

6 Download the skeleton class for TEMPERATURE from F/eprog-0001/exercises/ex4/temperature.e and put it into your project. Implement the class TEMPERATURE. Note that the conversion features are queries and thus should not change the existing object (no side effects), but create new objects. Do not forget to add contracts (temperature objects have obvious invariants and class TEMPERATURE should capture them). Feature make in class TEMPERATURE APPLICATION should use the TEMPERA- TURE class to do the following: 1. Ask the user to enter a temperature in Celsius. 2. Create a temperature object with the input value. 3. Convert the temperature to Fahrenheit and display it. 4. Convert the temperature to Kelvin and display it. 5. Repeat points 1 4 for temperatures in Kelvin and Fahrenheit. The execution of your application should yield the result shown in figure 2. Figure 2: Console To hand in Submit the class files for TEMPERATURE and TEMPERATURE APPLICATION. 3 It s Logic! To do 1. Describe the difference between non-strict and strict boolean operators. 2. Explain when you would prefer non-strict operators over strict operators and give an example for: and 6

7 and then or or else To hand in Hand in your solution to the two questions above. 7