1. Exceptions Review
Checked Vs. Unchecked Exceptions
Multiple Catch Blocks

2. Review Exception: An error caused by exceptional circumstance
An object that is thrown when an exception occurs
9/3/2019
Wendi Jollymore, ACES

3. Review: try-catch Block
9/3/2019
Wendi Jollymore, ACES

4. Review: Declaring Exceptions
Methods that don’t handle their own exceptions should declare them
9/3/2019
Wendi Jollymore, ACES

5. Review: Exercise
Write a program that asks the user for a numeric value via Input Dialog
Parse the number into an integer
print the square of that number on the console
Run the program and test it with a string value
What exception occurs?
Check the stack trace
9/3/2019
Wendi Jollymore, ACES

6. PROG 10082 - Object Oriented Programming 1
9/3/2019
Exceptions Hierarchy
Internal System Errors: Not much you can do about them.
9/3/2019
Wendi Jollymore, ACES
Wendi Jollymore, ACES

7. PROG 10082 - Object Oriented Programming 1
9/3/2019
Exceptions Hierarchy
Execution errors you can catch and handle in your code
9/3/2019
Wendi Jollymore, ACES
Wendi Jollymore, ACES

8. Exceptions Hierarchy
A child exception object can be caught if parent is caught
9/3/2019
Wendi Jollymore, ACES

9. Checked vs. Unchecked Exceptions are either Checked or Unchecked
You must handle them in some way
You may not ignore them
Unchecked Exceptions:
They can go “unchecked”
You’re not required to handle them
9/3/2019
Wendi Jollymore, ACES

10. Checked vs. Unchecked Checked Exceptions Example
You may not compile a program with checked exceptions that are not caught or declared.
9/3/2019
Wendi Jollymore, ACES

11. Checked vs. Unchecked Unchecked Exception classes, examples:
NumberFormatException
InputMismatchException
StringIndexOutOfBoundsException
NullPointerException
IllegalArgumentException
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Wendi Jollymore, ACES

12. Checked vs. Unchecked How do you know which is which? Unchecked
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13. Exceptions and the Call Stack
Call Stack is the “breadcrumb trail” of calling methods in a program
Exceptions can be thrown up the call stack to be handled by one main method
See example:
9/3/2019
Wendi Jollymore, ACES

14. Multiple Catch Blocks
What if you have more than one kind of exception occurring and you desire different actions for each?
A try catch can have more than one catch block
One for each exception you want to handle
Only one catch block will execute
9/3/2019
Wendi Jollymore, ACES

15. Multiple Catch Blocks
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Wendi Jollymore, ACES

16. Multiple Catch Blocks: Error!
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17. Exercise
Design a program that calculates the difference between two times
User enters a string in the form hh:mm:ss for two different amounts of time
long getTotalSeconds(String time)
Accepts one amount of time as a string and extracts hours, mins, seconds
Calculates and returns the total amount of time (hours * mins * 60 + seconds)
Helper methods getHours(), getMinutes(), getSeconds()
9/3/2019
Wendi Jollymore, ACES

18. Exercise, continued To test, ask user for two time amounts
Display difference in seconds
What exceptions could occur in your methods?
Should you put try-catch blocks in any method that might throw exceptions?
Is there an easier way?
Answer and code provided in class and in notes
9/3/2019
Wendi Jollymore, ACES