Lab: Gaining Experience Creating Exception Classes

Instructions: Answer the following questions one at a time. After answering each question, check your answer (by clicking on the check-mark icon if it is available) before proceeding to the next question.

Getting Ready: Before going any further, you should:

Depending on your development environment, create either a directory or a project for this lab.
Download the following files:

Person.java
PersonReader.java

to an appropriate directory/folder (e.g., the course downloads directory/folder). In most browsers/OSs, the easiest way to do this is by right-clicking/control-clicking on each of the links above and then selecting Save as... or Save link as....

1. Review: This part of the lab is a brief review of exception handling in Java.

Add an explicit value constructor to the PersonReader class that is passed a File object and instantiates scanner. What code did you add?
.
public PersonReader(File file) throws FileNotFoundException { scanner = new Scanner(file); }
Compile the PersonReader class to make sure your changes are syntactically correct. What exception did you have to catch or specify (i.e., re-throw)?
.

FileNotFoundException
Should you catch this exception or specify it (i.e., re-throw it)? Why?
.

You should specify it because there is no way for you to correct the problem.
The Integer.parseInt(java.lang.String) method throws NumberFormatException . Why don't you have to catch or specify (i.e., re-throw) this exception?
.

It is an unchecked exception (because it is a descendant of RuntimeException .

2. Creating Exception Classes: This part of the lab will give you some experience with creating exception classes (and using them).

Modify the createPerson(String) method in the Person class so that it throws a NumberFormatException if the age portion of the String cannot be converted to an int. What code did you add?
.
public static Person createPerson(String s) throws NumberFormatException,

Modify the readPerson() method in the PersonReader class so that it catches the NumberFormatException and creates a fictitious person with default values for the various attributes. What code did you add?


                                           try
       {
          result    = Person.createPerson(line);
       }
       catch (NumberFormatException nfe)
       {
          result    = new Person("Fictional Person",65,
                                 "540","568","1671");          
       }

Modify the createPerson(String) method in the Person class so that it also throws a NumberFormatException if the area code, exchange, or extension do not represent valid integers. (Hint: You don't have to add a throw statement.) What code did you add?
.
// Check the area code, exchange, and extension Integer.parseInt(areaCode); Integer.parseInt(exchange); Integer.parseInt(extension);
Create a checked NumericValueException class that only has a default constructor. The resulting Exception object must have an appropriate description. What code did you write?
.
public class NumericValueException extends Exception { public NumericValueException() { super("Invalid numeric value"); } }

Modify the createPerson(String) method in the Person class so that it no longer throws a NumberFormatException if the age is not an int. Instead, it must now throw a NumericValueException. (Hint: You will need to catch the NumberFormatException.) What code did you add?


                                        public static Person createPerson(String s) throws NumberFormatException,
                                                       NumericValueException

and


                                           try
       {
          age       = Integer.parseInt(token);
       }
       catch (NumberFormatException nfe)
       {
          throw new NumericValueException();          
       }

Modify the readPerson() method in the PersonReader class so that it catches the NumericValueException and creates a fictitious person with default values for the various attributes. What code did you add?
.
catch (NumericValueException nve) { result = new Person("Fictional Person",65, "540","568","1671"); }
Add an explicit value constructor to the NumericValueException class that is passed an int. The resulting Exception object must have a description that includes the text "Invalid numeric value: " and the parameter value. (Note: You will use this constructor later.) What code did you add?
.
public NumericValueException(int n) { super("Invalid numeric value: " + n); }
Modify the createPerson(String) method in the Person class so that it prints a message and then re-throws the NumberFormatException if the age is not an int and throws a NumericValueException if the age is an int and less than 18. What code did you add?
.
try { age = Integer.parseInt(token); if (age < 18) throw new NumericValueException(); } catch (NumberFormatException nfe) { throw nfe; }
Modify the readPerson() method in the PersonReader class so that when it catches the NumericValueException it creates a fictitious person named "Young Person" with default values for the other attributes. What code did you add?
.
catch (NumericValueException nve) { result = new Person("Young Person",65, "540","568","1671"); }
Add an explicit value constructor to the NumericValueException class that is passed a Throwable that is used as the cause. What code did you add?
.
public NumericValueException(Throwable cause) { super("Invalid numeric value", cause); }

Modify the createPerson(String) method in the Person class so that it throws a NumericValueException that contains the NumberFormatException as the cause if the age is not an int. What code did you add?


                                           try
       {
          age       = Integer.parseInt(token);

          if (age < 18) throw new NumericValueException(age);
       }
       catch (NumberFormatException nfe)
       {
          throw new NumericValueException(nfe);
       }

Modify the readPerson() method in the PersonReader class so that when it catches a NumericValueException without a cause it creates a fictitious person named "Ageless Person" with default values for the other attributes. (Hint: Use the inherited Throwable.getCause()

method.) What code did you add?


                                           catch (NumericValueException nve)
       {
          if (nve.getCause() == null)
          {
             result    = new Person("Young Person",65,
                                    "540","568","1671");          
          }
          else
          {
             result    = new Person("Ageless Person",65,
                                    "540","568","1671");          
          }
       }