1. Phil Tayco Slide version 1.0 Created Nov. 26, 2017
More Exercises
Phil Tayco
Slide version 1.0
Created Nov. 26, 2017

2. More Practice
Problem statement: Design a class infrastructure that manages payroll for a department as follows:
All departments have at most 10 employees
Employees are either paid hourly or weekly
All employees have a numeric id and a name
Hourly employees have an hourly pay rate
Salary employees have a weekly pay rate
Demonstrate this program by showing different employees added to the department and reporting the following:
Total monthly pay for all department employees
Who is paid the highest and lowest

3. More Practice
A prime benefit of OO design is the infrastructure giving you power to handle change
New problem requirements:
Years of service for every employee
Create a commission based employee who gets a percentage of total sales for pay
Given multiple departments, how do we find out which department gets paid more? How do we find out which employee in all departments is the highest paid?

4. Observations
To be discussed

5. Static and Final
Classes may contain properties and methods that may not require an object to be created for it to be used
public double calculateArea() {
return Math.PI * radius * radius; }
“Math.PI” is a property in the Math class and is static
When a method or property is public and static, it means you can use it without having the need to create an object
In this example, we don’t have to create a Math object to use PI. We are simply accessing the definition of it made public to us through the Math class
This makes sense because there really isn’t a need to use memory for concepts that are fundamentally fixed (their definition is “static”)

6. Static and Final
Notice PI is also in all caps. This is the standard Java notation to define a constant
Constants in classes are often static and made public to show certain fixed information associated with the concept of the class
In our example, we can design that all departments have a fixed maximum number of employees:
public class Department {
public final static MAX_EMPLOYEES = 10; }
This can be used by code in the Department class as well as outside it as needed
Constants help make code readable and when used properly, can be adjusted to maximum code change efficiency (i.e. changing the max in a department to 50)

7. Interfaces
Java also supports a special type of abstract class called an interface
Interfaces are restricted to defining only abstract methods and can be thought of as a form of a superclass
public interface Payable {
public double calculateMonthlyPay(); }
Any subclass can inherit from this through coding that the class will “implement” the interface:
public class Employee implements Payable
This gets the same treatment as a subclass inheriting from an abstract class like “Payable” in that it must now define “calculateMonthlyPay” (or else Employee must be abstract)

8. Interfaces
Interfaces only define method signatures and is a form of an abstract class
There are two differences with abstract classes and interfaces:
Abstract classes can still contain properties and methods that can be inherited. Interfaces only define abstract methods
Subclasses in Java can only “extends” one superclass. Subclasses that “implements” interfaces can implement multiple interfaces
More examples can and should be practiced from these concepts

9. Another Example
Design and implement a prototype that manages sales of computer products for employees
Sales employees are identified by a name and number
A record of up to 1000 sales transactions is maintained for each sales employee
Sales transactions are either standard or bulk
Standard transactions are identified by a number, a product sold and the quantity sold for that product
Bulk transactions are also identified by a number and up to 100 products for the sale
Bulk transactions also can have a discount amount for the sale

10. Another Example Computer products are either hardware or software
Hardware products are identified by name, price and manufacturing company
Software products are identified by name, price, developer company and software version number
The management system allows for creation of up 5 sales employees, recording sales and reporting employee performance
When a sale is recorded, the sales employee is identified for the sale and the type of transaction
Employee performance shows each sales transactions and the total revenue of them all

11. Observations
The main program is complex and is separate from the class design allowing it to be developed in different ways (command line, windows or web application)
Composition and Polymorphism: Sales Employee containing an array of Sales Transactions and Transaction types containing use of Products
Inheritance: Software and Hardware products inheriting basic information from Product. Standard and Bulk transactions inherit from Sales Transaction
Abstract classes: Sales Transaction is abstract requiring calculating sale in the subclasses

12. Programming Project Create a task management planner program
Tasks have a description and are either time constrained or either dependent or independent of other tasks
Time constrained tasks have a start and end date and time. Time constrained tasks cannot overlap (If one time constrained task is for 2pm-4pm on a given day, a second time constrained task such as from 3pm-5pm on the same day would not be allowed)
Once the end date and time have passed for a time constrained task, the task is considered to be complete
Time constrained tasks can also be marked as complete before the end date and time is reached

13. Programming Project Create a task management planner program
Dependent and independent tasks are not time constrained and only have a start date (no start time needed)
Independent tasks are considered started once the start date is reached
Dependent tasks have another task (which can be dependent or independent in itself) that it depends on to be completed as well as its own start date
Dependent tasks can only start if the start date is reached and the task it is dependent on is considered complete
Once any of these tasks are started, they are considered finished when the task is manually marked as complete

14. Programming Project
To simulate and test the task management planner, create a calendar where you can manually change the current date and time
As the current date and time is updated in the calendar, all task statuses are updated as needed
The main planning program shall allow for the following features:
Create a new task
Change the current date and time
Mark a task as complete
Report tasks
Features 1-3 should obtain the necessary information to perform the function with appropriate error handling
Reporting tasks should at least include listing all tasks, which ones have not started, started and complete

15. Programming Project
Data for tasks should be persistent and should be saved/loaded to a text file or database
The requirements list is somewhat open-ended by design. You are free to design your classes and implement your main program as you like. Any questions should be asked sooner rather than later
Programming requirements are to demonstrate all concepts discussed in class: Class design, use of composition, inheritance, polymorphism, error handling and data saving
Program can and encouraged to be developed in teams of at most, 2 people. Single individual development is acceptable, but requirements list does not change if you’re doing it by yourself
Program is due for demonstration on the last day of class