Chapter 9 Object-Oriented Software Development F Software Development Process F Analyze Relationships Among Objects F Class Development F Class Design Guidelines F Wrapper Classes F Generic Sort Class F Generic Matrix Class F Generic Linked List Class

Software Development Process

Relationships among Classes F Association F Aggregation F Inheritance

Association Association represents a general binary relationship that describes an activity between two classes.

Association, cont. An association is usually represented as a data field in the class. public class Course { private Faculty faculty; /**Constructors*/ /**Methods*/ }

Aggregation Aggregation is a special form of association, which represents an ownership relationship between two classes. Aggregation models the relationship like has-a, part-of, owns, and employed-by.

Inheritance Inheritance models the is-a relationship between two classes.

Inheritance public class Student extend Person { /**Constructors*/ /**Methods*/ } public class Faculty extend Person { /**Constructors*/ /**Methods*/ }

Class Development 1. Identify classes for the system. 2. Describe attributes and methods in each class. 3. Establish relationships among classes. 4. Create classes.

Example 9.1 Borrowing Mortgages Name BorrowerPersonMortgageAddress

Example 9.1 Borrowing Mortgages, cont. The following is a test program that uses the classes Name, Person, Address, Borrower, and Mortgage. BorrowMortgage Run

Example 9.2 The Rational Class RationalRunTestRationalClass

Class Design Guidelines F Hide private data and private methods. F A property that is shared by all the instances of the class should be declared as a class property. F Provide a public default constructor and override the equals method and the toString method defined in the Object class whenever possible.

Class Design Guidelines, cont. F Choose informative names and follow consistent styles. F A class should describe a single entity or a set of similar operations. F Group common data fields and operations shared by other classes.

Wrapper Classes F Boolean F Character F Short F Byte F Integer F Long F Float F Double

The Integer Class and The Double Class F Constructors  Class Constants MAX_VALUE, MIN_VALUE F Conversion Methods

Example 9.3 Sorting an Array of Objects Objective: The example presents a generic method for sorting an array of objects. The objects are instances of the Comparable interface and they are compared using the compareTo method. Generic Sort Run

Example 9.4 Designing Generic Classes F Objective: This example gives a generic class for matrix arithmetic. This class implements matrix addition and multiplication common for all types of matrices. GenericMatrix

Example 9.4, cont.

F Objective: This example gives two programs that utilize the GenericMatrix class for integer matrix arithmetic and rational matrix arithmetic. TestIntegerMatrix Run TestRationalMatrix Run Rational Matrix IntegerMatrix

Linked List Arrays are useful for storing and managing a set of elements of the same type. However, since the length of an array is fixed once the array is created, you need to know the length of the array before you create it. A linked list can grow or shrink dynamically as needed. A linked list consists of nodes, as shown in Figure Each node contains an element and each node is linked to its next neighbor. Thus, a node can be defined as a class as follows:

Linked List Structure public class Node { Object element; Node next; public Node(Object o) { element = o; }

Create a Linked List with three Nodes Node n1 = new Node(new String(“Welcome to Java!”)); Node n2 = new Node(new JButton(“OK”)); Node n3 = new Node(new Rational(1, 2)); n1.next = n2; n2.next = n3; Node first = n1; Node last = n3;

Generic Linked List Add a new node

Generic Linked List Remove a new node

Example 9.5 Using Linked List F This example creates a linked list using GenericLinkedList. It then uses the add method to add strings to the list and uses the remove method to remove strings from the list. GenericLinkedList Run TestLinkedList

Generic Linked List GenericLinkedList list = new GenericLinkedList(); list.addLast(new String(“Welcome to Java”)); list.addLast(new JButton(“OK”)); list.addLast(new Rational(1, 2));