Structural Programming Course Content and Data Structures - PDF document

Structural Programming Course Content and Data Structures • Introduction • Vectors • Objects • Testing/Debugging Winter 2000 • Methods • Arrays • Tracing Programs • Searching CMPUT 102: Sharing Resources • Object State • Files I/O • Sharing resources • Sorting Dr. Osmar R. Zaïane • Selection • Inheritance • Repetition • Recursion University of Alberta  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 1  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 2 2 Objectives of Lecture 13 Outline of Lecture 13 Common Resources Common Resources – – Static Variables and Methods Static Variables and Methods • Understand the use of static variables to share • Static variables common information between instances of the • Static methods same class. • Adventure Version 4 • Study the use of static methods to perform computations that independent of any object. • Re-write the Adventure program using some useful static variables .  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 3  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 4 Static Variables Resources Common to a Class • It is wasteful to require every object in a class to • Sometimes common sharable resources are use an instance variable to access these common needed by each object in a class. resources. – (DFK &LUFOH REMHFW PD\ QHHG WKH YDOXH RI � VR • Instead, we can define a static variable in the it can compute and return its area. class that can be bound to this common resource: – Each TreasureChest object may need a common maximum number of tokens so it can generate a public class Circle … random number ≤ this number when it is private static final float pi = 3.14159f; constructed (initialized). public class TreasureChest … – Each TreasureChest object may need a random private static final int maxTokens = 10; number generator object to generate its initial private static RandomInt generator; number of tokens. generator = new RandomInt(1);  Dr. Osmar R. Zaïane, 2000  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 5 Structural Programming and Data Structures University of Alberta 6 1

Object Independent Actions Outline of Lecture 13 • Some actions are not performed by a • Static variables specific instance of a class. • Static methods – Start an application program. • Adventure Version 4 – Perform an operation on some values. • In fact, no instance may even need to exist for these actions to be performed.  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 7  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 8 Static Methods Outline of Lecture 13 • A static method or class method is code that can be executed without sending a message to any object: • Static variables public class OurProgram … • Static methods public static void main(String args[]) public class String … • Adventure Version 4 public static String valueOf(int i) • The syntax of static method calls looks like a message is being sent to a class: String.valueOf(3) � “3” • However, no message is actually involved.  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 9  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 10 Adventure Version 4 Adventure - Code Change Summary • We are going to add some functionality to the Arithmetic Adventure game . • In the Adventure class we will: • We will put treasure chests in rooms. – replace the method enterRoom(Adventurer) • Add a class called Chest. • When the adventurer tries to open a chest we will generate an arithmetic question. • Add a class called Question. • The chest will contain a random number of • Add a class called RandomInt tokens that will be added or subtracted to the • Leave the Adventurer class unchanged. adventurer's total, depending on whether the adventurer answers the question correctly.  Dr. Osmar R. Zaïane, 2000  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 11 Structural Programming and Data Structures University of Alberta 12 2

Running Adventure 4 Program - Adventure 4.1 import java.util.*; NO CHANGES public class Adventure { /* Version 4 This program is an arithmetic adventure game … */ /* Constructors */ public Adventure () { /* Initialize an adventure by creating the appropriate objects. */ }  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 13  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 14 NO CHANGES Program - Adventure 4.3 Program - Adventure 4.2 /* Private Instance Methods */ NO CHANGES /* Main program */ private void play() { /* public static void main(String args[]) { Plays the Adventure game. Adventure game; */ game = new Adventure(); Adventurer adventurer; game.play(); } adventurer = this.greeting(); this.enterRoom(adventurer); this.farewell(adventurer); }  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 15  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 16 Program - Adventure 4.4 Program - Adventure 4.5 NO CHANGES NO CHANGES private Adventurer greeting() { /* System.out.print("Well "); Great the user and answer an Adventurer that System.out.print(playerName); represents the user. System.out.println (", after a day of hiking you spot a silver cube." ); */ System.out.println ("The cube appears to be about 5 meters on each side." ); String playerName; System.out.println ("You find a green door, open it and enter." ); System.out.println (" The door closes behind you with a soft whir and disappears." ); System.out.println(" Welcome to the Arithmetic Adventure game. "); System.out.println ( " There is a feel of mathematical magic in the air." ); System.out.print("The date is "); Keyboard.in.pause(); System.out.println(new Date()); return new Adventurer(playerName); System.out.println(); } System.out.print("What is your name?"); playerName = Keyboard.in.readString();  Dr. Osmar R. Zaïane, 2000  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 17 Structural Programming and Data Structures University of Alberta 18 3

Program - Adventure 3.6 Program - Adventure 4.6 private void enterRoom(Adventurer adventurer) { /* private void enterRoom(Adventurer adventurer) { OLD The given adventurer has entered the /* NEW first room. The given adventurer has entered the */ first room. Integer myTokens; */ Chest chest; System.out.print(" How many tokens would you like, "); System.out.print(adventurer.name()); chest = new Chest(); System.out.print("?"); chest.display(); myTokens = Keyboard.in.readInteger(); adventurer.gainTokens(myTokens.intValue()); chest.open(adventurer); } }  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 19  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 20 Program - Adventure 4.7 Class - Chest 4.1 NO CHANGES import java.util.*; public class Chest { /* private void farewell(Adventurer adventurer) { An instance of this class represents a treasure chest in /* the Adventure game. A Chest contains a number of tokens. Say farewell to the user and report the game result. */ */ /* Constructor */ public Chest() { System.out.print("Congratulations "); /* System.out.print(adventurer.name()); Initialize me so that I contain a random number of System.out.print(" you have left the game with "); tokens. System.out.print(adventurer.tokens()); */ System.out.println(" tokens."); this.tokens = Chest.generator.next(Chest.maxTokens); } }  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 21  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 22 Class - Chest 4.3 Class - Chest 4.2 public void open(Adventurer adventurer) { /* Ask the user an arithmetic question and if a correct /* Instance Methods */ answer is given, add tokens to the given Adventurer. If it is answered incorrectly, remove tokens. */ public void display() { Question question; /* Output a description of myself. question = new Question(); */ question.ask(); // We really want to do only one of the next two System.out.println("There is a small carved chest in the center of // lines, depending on the user’s answer. the room."); System.out.println("It appears to be a treasure chest!"); this.correctAnswer(adventurer); this.wrongAnswer(question, adventurer); } }  Dr. Osmar R. Zaïane, 2000  Dr. Osmar R. Zaïane, 2000 Structural Programming and Data Structures University of Alberta 23 Structural Programming and Data Structures University of Alberta 24 4