1. Problem Solve
Suppose a librarian needs to keep track of all the books in a library. How would we write a program to solve this problem?

2. Class
Problem Suppose a librarian needs to keep track of all the books in a library. What would be the class for this project?

3. Class
Problem Suppose a librarian needs to keep track of all the books in a library. What would be the class for this project? Library

4. Class
Problem Suppose a librarian needs to keep track of all the books in a library. What would be the class for this project? Library How would I declare this Library class?

5. Class
Problem Suppose a librarian needs to keep track of all the books in a library. What would be the class for this project? Library How would I declare this Library class? public class Library

6. Data
Problem Suppose a librarian needs to keep track of all the books in a library. What data or information about the Library do we have?

7. Data
Problem
Suppose a librarian needs to keep track of all the books in a library.
What data or information about the Library do we have?
librarian name
collection of books

8. How do we store this data in our class?
Data Storage
How do we store this data in our class?
librarian name
collection of books

9. How do we store this data in our class?
Data Storage
How do we store this data in our class?
librarian name
String
collection of books
ArrayList of String

10. private ArrayList<String> books;
Data Storage
How is it defined in the class?
librarian name
String
private String librarian;
collection of books
ArrayList of String
private ArrayList<String> books;

11. Code
import java.util.ArrayList; public class Library { private String librarian; private ArrayList<String> books; public Library(String librarianName) librarian = librarianName; books = new ArrayList<String>(); } methods omitted …

12. Class Diagram
import java.util.ArrayList; public class Library { private String librarian; private ArrayList<String> books; public Library(String librarianName) librarian = librarianName; books = new ArrayList<String>(); } methods omitted …

13. Class Diagram
import java.util.ArrayList; public class Library { private String librarian; private ArrayList<String> books; public Library(String librarianName) librarian = librarianName; books = new ArrayList<String>(); } methods omitted …
Library

14. myLibrary = new Library(“Mrs. Jones”);
Object Diagram
Now suppose there is a specific library named myLibrary with a librarian named Mrs. Jones.
We would execute the following to create it:
myLibrary = new Library(“Mrs. Jones”);
What does new really do?
1) it creates a new class instance of the object
2) it also executes the constructor for the class

15. myLibrary = new Library(“Mrs
myLibrary = new Library(“Mrs. Jones”); 1) it creates a new class instance of the object
import java.util.ArrayList; public class Library { private String librarian; private ArrayList<String> books; public Library(String librarianName) librarian = librarianName; books = new ArrayList<String>(); } methods omitted …
myLibrary:
Library
new
librarian
books
null

16. myLibrary = new Library(“Mrs
myLibrary = new Library(“Mrs. Jones”); 2) it also executes the constructor for the class
import java.util.ArrayList; public class Library { private String librarian; private ArrayList<String> books; public Library(String librarianName) librarian = librarianName; books = new ArrayList<String>(); } methods omitted …
librarianName
myLibrary:
Library
:String =
librarian
books
“Mrs. Jones”
new
:ArrayList<String>

17. Adding ArrayList Items
myLibrary:
Library
:String
“Mrs. Jones”
Now suppose we added 2 book names to our books field using external calls to the ArrayList .add method:
books.add(“Wuthering Heights”);
books.add(“Little Women”);
librarian
books
:ArrayList<String>
.add
:String
.add
“Wuthering Heights”
:String
“Little Women”

18. Object Diagram Complete object diagram contains:
1 instance of a Library class object named myLibrary
1 String object with value “Mrs. Jones” that field librarian points to
1 ArrayList object with 2 String items that field books points to
2 String objects with values “Wuthering Heights” & “Little Women ” that index 0 & 1 of the ArrayList points to
myLibrary:
Library
:String
“Mrs. Jones”
librarian
books
:ArrayList<String>
:String
“Wuthering Heights”
:String
“Little Women”