COMP 14 Introduction to Programming Miguel A Otaduy June 3 2004 Review Homework 5 Algorithm How to solve the problem without objects not totally true Strings are objects too How to solve the problem with objects Algorithm Create teams Create semifinal games Output initial message Get score of semifinal 1 Determine finalist 1 Get score of semifinal 2 Determine finalist 2 Create final game Get score of final Determine winner Without objects String UNC UNC String Duke Duke String semi1 UNC Vs Duke String finalist1 if score1 score2 finalist1 UNC else finalist1 Duke Add method String UNC UNC String Duke Duke String semi1 UNC Vs Duke String finalist1 finalist1 gameWinner semi1 score1 score2 UNC Duke With objects Team Team Game Team UNC new Team UNC Duke new Team Duke semi1 new Game UNC Duke finalist1 finalist1 semi1 gameWinner score1 score2 What s going on String name UNC Team UNC Team Duke Game semi1 String name Duke Team objects Team finalist1 Reference variables Team team1 Team team2 Game object What is different We declare data inside objects not directly in the main method The Strings become data members of the Team objects We no longer need Strings for the games If we don t use objects we duplicate the data The String for the game can be generated using the ones stored in the Teams The method gameWinner is a method associated to a particular game object No need to pass the game as a parameter No need to pass the teams as parameters Why does the code look almost the same Because Strings and Teams and Games are ALL classes objects Our classes are simply wrappers of Strings Structure of a Team object Data String name Methods Constructors toString Structure of a Game object Data Pointer to team1 Team team1 Pointer to team2 Team team2 Methods Constructors toString gameWinner receives as parameter the score and returns the pointer to the winner team Classes Objects are collections of data and operations methods We need to define the pattern footprint of objects classes Writing classes public class ClassName Data members private int a Constructor s public ClassName Code of the method other methods public return type method1 type param1 type param2 Code of the method Writing the main public class MainClassName Data members Static BufferedReader keyboard main method public static void main Code of the main method other methods public static return type method1 type param1 Code of the method This is wrong public class ClassName Data members No private int a Constructor s instructions directly in the body of a class They have to be inside a method Exception initialization of a static variable e g keyboar OtherClass obj new OtherClass other methods public return type method1 type param1 Code of the method Review 0 1 2 3 Arrays Declaration int counts Instantiation counts new int 50 Initialization Access for int i 0 i counts length i counts i 0 Initializer List declaration instantiation and initialization double grades 98 7 72 4 87 5 int numbers num num 1 num 2 num 3 can use variables and expressions as initial values Arrays and Assignment int counter new int 5 temp int temp temp counter doesn t make a copy of the array temp counter is true since the reference variables contain the same address 0 1 2 3 4 counter Copying Arrays counter int counter 1 2 3 4 5 int temp new int counter length temp 0 1 2 3 4 1 2 3 4 5 for int i 0 i counter length i temp i counter i 1 0 1 2 3 2 3 4 4 5 i 1 4 2 5 0 3 References and Assignment counter temp counter temp 0 1 2 3 4 1 2 3 4 5 Remember that arrays use reference variables just like objects 0 1 2 3 4 1 2 3 4 5 References and null temp null null is a reserved word that means empty nothing counter temp 0 1 2 3 4 1 2 3 4 5 Remember that arrays use reference variables just like objects 0 1 2 3 4 1 2 3 4 5 Arrays as Parameters Entire array can be passed as a parameter method can change elements of the array permanently since we re passing a reference Elements of an array can be passed as parameters too normal rules apply public class Tester public static void swap int scores int x int y int temp scores x 30 scores 2 20 scores x scores y scores 3 30 20 scores y temp temp 20 public static void main String args int grades new int 4 for int i 0 i grades length i grades i i 10 swap grades 2 3 grades 2 30 20 grades 3 20 30 Arrays of Objects Can use arrays to manipulate objects Create array of objects classname array new classname size Must instantiate each object in array for int j 0 j array length j array j new classname Example 16 students Each student String name int age String major int year Create arrays of all the data Problem print the names according to increasing age Analyze without objects or with objects Why To do Homework 6 Start with requirements 1 and 4 Objects classes Exercise Create classes House and Roommate House will have an array of Roommates Create methods to set number of Roommates etc whatever you come up with Test the classes by writing calls to the methods in the main method Come to discuss problems