ECE 462Object-Oriented Programmingusing C++ and JavaLecture 3Yung-Hsiang [email protected] 2 2Mini Reviewconcepts explained so far:• object: identity, states (attributes), behavior (methods)• class: interface and implementation• inheritance: code reuse• polymorphism: different derived classes have different behavior• encapsulation: hide information inside objectsweek 2 3Execute C++ and Java Programs•C++– Linux: g++– Windows: g++ in cygwin•Java– Linux: javac to compile and java to execute or Netbeans to compile and execute– Windows: javac to compile and java to execute or Netbeans to compile and executeweek 2 4//AddArray.javapublic class AddArray { //(A)public static void main( String[] args ) //(B){int[] data = { 0, 1, 2, 3, 4, 5, 9, 8, 7, 6 }; //(C)System.out.println( "The sum is: " //(D)+ addArray(data) ); }public static int addArray( int[] a ) { //(E)int sum = 0; for ( int i=0; i < a.length; i++ ) sum += a[i]; return sum; }}similar to (int argc, char * argv[]) in Csimilar to printf in Cweek 2 5//Polymorph.javaclass User { private String name;private int age;public User( String str, int yy ) { name = str; age = yy; } public void print() { System.out.print( "name: " + name + " age: " + age ); }} // ; not needed for Javaclass StudentUser extends User { // derived class private String schoolEnrolled;public StudentUser( String nam, int y, String sch ) { super(nam, y); // User::print(); in C++ schoolEnrolled = sch;}public void print() { super.print(); System.out.print( " School: " + schoolEnrolled );}}week 2 6class Test {public static void main( String[] args ) {User[] users = new User[3]; users[0] = new User( "Buster Dandy", 34 ); users[1] = new StudentUser("Missy Showoff",25,"Math"); users[2] = new User( "Mister Meister", 28 ); for (int i=0; i<3; i++) { users[i].print(); System.out.println(); }}}Encapsulation– users[2].name ⇒ compile-time error– users[2].age ⇒ compile-time error– Information is available only if an object allows the visibility; visibility is specified in the class interface.week 2 7• Inheritance: – A derived class has all the public and protected properties (= attributes + methods) of the base class. Private properties are not inherited.– A pointer for a base class can point to an object of a derived class.– A pointer for a derived class can not point to an object of a base class.– A StudentUser is a User, incorrect the other way• Polymorphism: – A pointer's behavior changes based on the object being pointed to.– determined at run-timeweek 2 8Polymorphism• users[1] = new StudentUser("Missy Showoff",25,"Math");– behavior as a StudentUser– users[1].print will include the school• users[1] = new User("Missy Showoff",25);– behavior as a User – users[1].print will not include the schoolUserStudentUserweek 2 9Self TestWhat concept is used? Choose your answers from1. encapsulation2. inheritance3. polymorphismQuestions:• a StudentUser object can call super.print();• a StudentUser object can be assigned to (RHS) to a User object• in StudentUser’s print, accessing name is an error• users[0].print() and users[1].print() behave differentlyweek 2 10Self TestWhat concept is used? Choose your answers from1. encapsulation2. inheritance3. polymorphismQuestions:• a StudentUser object can call super.print(); ⇒ 2• a StudentUser object can be assigned to (RHS) to a User object ⇒ 2• in StudentUser’s print, accessing name is an error ⇒ 1• users[0].print() and users[1].print() behave differently ⇒3week 2 11class User { private String name;private int age;public User( String str, int yy ) { name = str; age = yy; } public void setAge(int newage) {// an example of information consistencyif (age > newage) { System.out.println("You can't become younger."); }else { age = newage; }}public void print() { System.out.print( "name: " + name + " age: " + age ); }}In general, it is a bad programming habit to provide “setXXX” methods, worse to make them public.week 2 12// ----------------------- User1.cc#include <iostream>#include <string>using namespace std;class User { string name; // default visibility is privateint age;public: User( string str, int yy ) { name = str; age = yy; } // constructorvoid print() { cout << "name: " << name << " age: " << age << endl; }}; // ; not needed for Javaint main(){User u( "Zaphod", 119 ); // create an objectu.print();return 0;}commentconstructor: a method with the same name as the classweek 2 13// ----------------------- User2.cc#include <iostream>#include <string>using namespace std;class User { string name;int age;public: User( string str, int yy ); void print();};User::User( string str, int yy ) {// this does not have to in the same file name = str; age = yy; } void User::print() { cout << "name: " << name << " age: " << age << endl; }int main(){User u( "Zaphod", 119 );u.print();return 0;}week 2 14// ----------------------- Polymorph.cc#include <iostream>#include <string>using namespace std;class User {string name; int age; public:User(string nm, int a) {name=nm; age=a;} virtual void print() { // virtual explained later cout << "Name: " << name << " Age: " << age; }};week 2 15class StudentUser : public User { string schoolEnrolled; // new attributepublic: StudentUser(string nam, int y, string school) : User(nam, y){ schoolEnrolled = school; }void print() { User::print(); // print a user's attribute cout << " School Enrolled: " << schoolEnrolled;}};week 2 16int main(){User* users[3]; users[0] = new User( "Buster Dandy", 34 ); users[1] = new StudentUser("Missy Showoff", 25, "Math");// a StudentUser is a Userusers[2] = new User( "Mister Meister", 28 ); for (int i=0; i<3; i++) { users[i]->print(); cout << endl;}// this program has a memory leak; ignore it for now return 0;}ECE 462Object-Oriented Programmingusing C++ and JavaLecture 4Yung-Hsiang [email protected] 2 18Self Test• Java: class Shape { ...}class Triangle ______ Shape { ...}•C++class Shape {