Feb 4, 2020 -- Notes

IT 313 -- Feb 4, 2020

Review Exercises

Order these items by containment order from largest to smallest:
```
Package  Method  Project  Class  Module 
```
Ans: For most projects, the containment order looks like this:
```
Project ⊃ Module ⊃ Package ⊃ Class ⊃ Module
```
However, it is possible for packages to be divided over several modules.
How do you specify that a class belongs to a package?
Ans: You put this line at the top of the class file:
```
package it313.ssmith;
```
How do you use a class A that belongs to a package?
Ans: You put this line at the top of the class to avoid typing it313.ssmith everytime you use the class A:
```
import it313.ssmith.A;
```
How do you use a class that belongs to a different module?
Ans: Suppose that Main is the class that uses the class Greeter and Main is in module2. Also suppose that the Greeter class is in module1. Then for the Main class to use the Greeter class, you set up a dependency for module2 on module1. Here is how you set up the dependency in module2 on module1:
1. ...
What is a wrapper class? How are wrapper classes used with ArrayList collections?
Look at the IntegerTest class in the InstanceMethodsExample project.
Ans: a wrapper class object contains a primitive datatype value. Here is the table of primitive types and their corresponding wrapper class types:

Primitive Type Wrapper Class

int Integer

double Double

char Character

boolean Boolean

Primitive Type	Wrapper Class
int	Integer
double	Double
char	Character
boolean	Boolean

Create a Main class to run this main method:

public static void main(String[ ] args) {
    int a = Integer.parseInt(args[0]);
    int b = Integer.parseInt(args[1]);
    System.out.println("Quotient: " + (a / b));
}

Set up try/catch blocks to handle exceptions that may occur
To let IntelliJ write the try/catch block, use

Code >> Surround With... >> try/catch

Ans: Here is the main method with a try/catch block added:

public class Main {
    public static void main(String[ ] args) {
        try {
            int a = Integer.parseInt(args[0]);
            int b = Integer.parseInt(args[1]);
            System.out.println("Quotient: " + (a / b));
        }
        catch (NumberFormatException e) {
            System.out.println("Non-numeric input.");
            System.exit(1);
        }
        catch (ArithmeticException e) {
            System.out.println("Division by zero.");
            System.exit(2);
        }
    }
}

Project 4

Look at the Project 4 Description.

Use the String object chars and String array codes to translate an input string into Morse code:

String chars = " ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
String[ ] codes = {"   ", ".-", "-...", "-.-.", "-..", 
    ".", "..-.", "--.", "....", "..", ".---", "-.-", 
    ".-..", "--", "-.", "---", ".--.", "--.-", ".-.", 
    "...", "-", "..-", "...-", ".--", "-..-", "-.--", 
    "--..", ".----", "..---", "...--", "....-", ".....", 
    "-....", "--...", "---..", "----.", "-----"};

Write a method named toMorseCode to perform the translation.
Ans: Here are the source code files.

Find a way to replace the dash in an extended zipcode such as "60604-2468" by the empty string ( "" ). Ans:

public static void main(String[ ] args) {
    String zipcode = "60604-2468;
    zipcode = zipcode.replace("-", "");
    System.out.println(zipcode);
}

Review of Inheritance

Consider this Employee Hierarchy UML diagram. Here is the short version of the UML diagram:
```
Person ← Employee ← Executive
```
An arrow in a UML diagram means "inherits from."

We know about private (can only use the object within the current class) and public (can use the object anywhere). In addition, we can use protected accessibility, which means that the item is accessible in the current class or in any derived class of the current class.
The is-a test is used to determine whether inheritance makes sense. For example, an Employee is a Person, so it makes sense to make Person the base class and Employee derived class.
Inheritance is the process of creating a derived class from a base class.
The derived class inherits all of the instance variables and methods from the base class.
The derived class can add additional instance variables and methods.
The derived class can also override (replace) methods in the base class with methods of the same name and signatuve that are more appropriate for the derived class.
A derived class object is a specialized version of a base class object with extra capabilities.
Look at the employeehierarchy Module in the Inheritance Example.
Practice Problems
1. Identify the base class and derived class in the following pairs of classes. Use the is-a test.
```
Employee   Manager

GraduateStudent   Student  

Person   Student  

Vehicle   Car      

Car   Minivan  

Truck   Pickup   
```
2. What are other terms for base class and derived class? Ans:
  
  Base Class Derived Class
  
  Parent Class Child Class
  
  Super Class Subclass
3. Identify the inheritance relationships between these classes. Use the is-a test.
```
Student   SeminarSpeaker   Professor   Person   TeachingAssistant
Course   Employee   Seminar   Secretary   Lecture   DepartmentChair
ComputerLab   Janitor   
```
Look at this module in the Inheritance Example:
socialnetwork

Project 5

Look at Project 5.
We have already seen how to set up a scanner to read from the Web (InputOutput Example).
See the JFreeChart Example to see how to create bar graphs.

Base Class	Derived Class
Parent Class	Child Class
Super Class	Subclass