Transcript Class & Object Diagrams

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?
Class
Problem
Suppose a librarian needs to keep track
of all the books in a library.
What would be the class for this project?
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
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?
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
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?
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
Data Storage
How do we store this data in our class?
librarian name
collection of books
Data Storage
How do we store this data in our class?
librarian name
String
collection of books
ArrayList of String
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;
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 …
}
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 …
}
Class Diagram
import java.util.ArrayList;
Library
public class Library
{
private String librarian;
private ArrayList<String> books;
public Library(String librarianName)
{
librarian = librarianName;
books = new ArrayList<String>();
}
methods omitted …
}
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
myLibrary = new Library(“Mrs. Jones”);
1) it creates a new class instance of the object
import java.util.ArrayList;
new
public class Library
{
private String librarian;
private ArrayList<String> books;
public Library(String librarianName)
{
librarian = librarianName;
books = new ArrayList<String>();
}
methods omitted …
}
myLibrary:
Library
librarian
null
books
null
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 …
}
myLibrary:
Library
librarian
librarianName
=
books
new
:ArrayList<String>
:String
“Mrs. Jones”
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”);
librarian
books
:ArrayList<String>
0
:String
1
.add
.add
“Wuthering Heights”
• books.add(“Little Women”);
:String
“Little Women”
Object Diagram
Complete object diagram
contains:
• 1 instance of a Library class object
named myLibrary
myLibrary:
Library
“Mrs. Jones”
librarian
books
:ArrayList<String>
0
• 1 String object with value “Mrs. Jones”
that field librarian points to
• 1 ArrayList object with 2 String
items that field books points to
:String
1
:String
“Wuthering Heights”
• 2 String objects with values
:String
“Wuthering Heights” & “Little Women ” that
“Little Women”
index 0 & 1 of the ArrayList points to