1. …WHAT YOU SHOULD HAVE LEARNED IN ETEC1101… IN JAVA 2. C => JAVA

2. THE PLAN… I'll show you something you (hopefully) recognize from C. We'll re-write it (together) in Java. As we go, we'll discuss differences… …and generate a (partial) list of them.

3. (STANDARD) INPUT / OUTPUT // In a file called whatever.c #include int main(int argc, char ** argv) { char name[256]; printf("Enter name: "); scanf("%s", name); printf("Hello, '%s'!\n", name); }

4. ARRAYS (ETEC1101 LAB2) // In a file called lab2.c #include int main() { const int NUM = 50; int i; double avg = 0, var = 0; int values[NUM]; // NUM *must* be const (why?) srand(time(NULL)); for (i=0; i<NUM; i++) { values[i] = rand() % 100 + 1; printf("%02d) %d\n", i, values[i]); avg += values[i]; } avg /= NUM; for (i=0; i<NUM; i++) var += (values[i] - avg) * (values[i] - avg); var /= NUM; printf("Avg: %f\nVar: %f\n", avg, var); return 0; }

5. FUNCTIONS (ETEC1101 LAB4-ISH) // In a file called blah_blah.c #include unsigned int count_word(char * text, char letter) { unsigned int count = 0; for (int i=0; i<strlen(text); i++) { if (text[i] == letter) count++; } return count; } int main() { char test_text[256]="Now is the winter of our discontent\n"; char test_letter = 's'; strcat(test_text,"Made glorious summer by this son of York"); printf("Text: \n\"%s\"\n", test_text); printf("\tOccurrences of '%c':", test_letter); printf("%u\n", count_word(test_text, test_letter)); return 0; }

6. C STRUCTURES / JAVA CLASSES C's closest approximation to OOP is structures No methods (associated functions), only attributes (variables) Usually, functions are used to modify a structure C separates the data (structures) from the code (functions / program). It is up to the programmer to connect them Java (and C++ and …) combine data and code to manipulate it into objects. A class is a description of a specific category of object. E.g. LinkedList, Spaceship, etc. An object is a variable of the category described by a class. E.g. My linked list of students; Player1 and Player2's spaceship. All objects share the same structure, but separate values from other instances of that class.

7. OOP IN JAVA Java is (almost) completely an OOP-based language. Our first few programs will have this structure: package xyz; // import statements public class ABC { protected int mAttr; // attribute public ABC(____) { /* code */} // constructor public void qrz(___) { /* code */ } // method public static void main(String[] args) { // Main code goes here. Usually we'll create // instances of abc and test them somehow. } } We'll explore the meaning of each part as we go. We'll also look at alternative organizations.

8. "OOP" (ETEC1101 LAB6-ISH) // In a file called student.h #ifndef _STUDENT_H_ #define _STUDENT_H_ // A new "type" description. All students will share this structure typedef struct { char mFName[64]; char mLName[64]; unsigned int mID; }Student; // Initializes a new student record with all relevant data. // IMPORTANT: s must point to a valid memory location OR ELSE! void init_student(Student * s, char * fname, char * lname, unsigned int id); // Prints the student to stdout void print_student(Student * s); #endif

9. "OOP" (ETEC1101 LAB6-ISH), CONT. // In a file called student.c #include "student.h" #include void init_student(Student * s, char * fname, char * lname, unsigned int id) { strcpy(s->mFName, fname); strcpy(s->mLName, lname); s->mID = id; } void print_student(Student * s) { printf("[%u: %s %s]\n", s->mID, s->mFName, s->mLName); }

10. "OOP" (ETEC1101 LAB6-ISH), CONT. // In a file called student_dbase.h #ifndef _STUDENT_DBASE_H_ #define _STUDENT_DBASE_H_ #include "student.h" // A new "type" description. All StudentDBase's will share this structure typedef struct { Student * mRecords; // Will be dynamically allocated as needed. unsigned int mNumRecords; }StudentDBase; // Initializes a student database. void init_dbase(StudentDBase * sd); // Destroys a student database. MUST BE CALLED to avoid a memory leak. // ALSO: init_dbase must've been called initially on this dbase. void destroy_dbase(StudentDBase * sd); // Adds a new student to the end of the database. void add_student(StudentDBase * sd, char * fname, char * lname, unsigned int id); // Removes a student for the database (no effect if not found) void remove_student(StudentDBase * sd, unsigned int id); // Returns the pointer to the student record with the given id, or NULL // if not found. Student * find_student(StudentDBase * sd, unsigned int id); // Prints all students to stdout void print_all(StudentDBase * sd); #endif

11. "OOP" (ETEC1101 LAB6-ISH), CONT. // In a file called student_dbase.c #include "student_dbase.h" #include "student.h" #include void init_dbase(StudentDBase * sd) { sd->mRecords = NULL; sd->mNumRecords = 0; } void destroy_dbase(StudentDBase * sd) { if (sd->mRecords) free(sd->mRecords); sd->mRecords = NULL; sd->mNumRecords = 0; }

12. "OOP" (ETEC1101 LAB6-ISH), CONT. // student_dbase.c, cont. void add_student(StudentDBase * sd, char * fname, char * lname, unsigned int id) { Student * new_records; // Re-allocate the array new_records = (Student*)malloc(sizeof(Student) * (sd->mNumRecords + 1)); if (new_records) { // Copy the old records to the new, if any if (sd->mNumRecords > 0) memcpy(new_records, sd->mRecords, sizeof(Student) * sd->mNumRecords); // Initialize the last one with the given data init_student(&new_records[sd->mNumRecords], fname, lname, id); // Copy new_records to sd's mRecord and increment the student count if (sd->mRecords) free(sd->mRecords); sd->mRecords = new_records; sd->mNumRecords++; } }

13. "OOP" (ETEC1101 LAB6-ISH), CONT. // student_dbase.c, cont. void remove_student(StudentDBase * sd, unsigned int id) { int pos = 0; Student * new_records = NULL; while (pos mNumRecords && sd->mRecords[pos].mID != id) pos++; if (pos != sd->mNumRecords) { if (sd->mNumRecords > 1) { // Re-allocate the array to be of a smaller size new_records = (Student*)malloc(sizeof(Student) * (sd->mNumRecords - 1)); if (new_records) { // Copy up to position pos from current records memcpy(new_records, sd->mRecords, sizeof(Student) * pos); // Copy everything after position pos from current records memcpy(&new_records[pos], &sd->mRecords[pos + 1], sizeof(Student) * (sd->mNumRecords – pos - 1)); } } // Copy new records to sd's mRecord and decrement the student count if (sd->mRecords) free(sd->mRecords); sd->mRecords = new_records; sd->mNumRecords--; } }

14. "OOP" (ETEC1101 LAB6-ISH), CONT. // student_dbase.c, finished Student * find_student(StudentDBase * sd, unsigned int id) { int i; for (i=0; i mNumRecords; i++) { if (sd->mRecords[i].mID == id) return &sd->mRecords[i]; } return NULL; } void print_all(StudentDBase * sd) { int i; for (i = 0; i mNumRecords; i++) print_student(&sd->mRecords[i]); }

15. "OOP" (ETEC1101 LAB6-ISH), CONT. // In a file, main.c #include "student_dbase.h" #include int main() { StudentDBase my_dbase; Student * temp; init_dbase(&my_dbase); add_student(&my_dbase, "Bob", "Smith", 14); add_student(&my_dbase, "Jane", "Doe", 83); add_student(&my_dbase, "Jake", "Dog", 56); remove_student(&my_dbase, 16); remove_student(&my_dbase, 83); temp = find_student(&my_dbase, 56); if (temp) strcpy(temp->mLName, "Human"); // Hmmm... print_all(&my_dbase); return 0; }

16. MINI-LAB [Try it first without looking back at the slides] Write a class called Foo Should have a private String attribute called theWord. Should have a public method named speakIt One parameter: an integer, n The method should output (on one line) theWord n times (no spaces) The main program (in the class) should… create two instances of Foo: one called Bob (his word is "kitten") and one called Sue (her word is "dragon"). Make Bob speakIt 5 times, Sue speakIt 3 times, then Bob speakIt 4 times. [A good example of a quiz question…]