Description
1 Introduction
This lab will focus on a powerful way to handle errors known as exceptions. You will demonstrate the ability to both throw and catch exceptions. Additionally, you will get a soft
introduction to GUI programming using JOptionPane. We recommend that you read about
JOptionPane in the Java API documentation.
2 Exercises
2.1 Combination
In the lab repository, you should see a Combination.java. For this exercise, you will write
a few methods for the Combination class. Read through the comments, and add your code
at the @todo markers.
c Christopher Newport University, 2016
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Exercise 1
Implement the following methods in the Combination class.
1. Create a constructor that receives three ints a, b, c and places them in the numbers
array in order. This makes a, b, c the combination which this object represents.
2. A method named getNumbers which returns a copy of the combination in order. This
method should not return numbers.
3. A method named isWithinRange which receives int upper which represents an upper bound and returns a boolean. This method returns true if each number in the
combination is in the closed interval [0, upper] and false otherwise.
Test your code against CombinationTest.java.
Exercise 1 Complete
Run:
git add .
git commit -m “Completed exercise 1”
git push origin master
2.2 Lock
Create a class named Lock that uses the provided class InvalidLockCombinationException,
which defines a new type of RuntimeException. We will be learning about inheritance and
extending classes later in the semester. Review the code for
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InvalidLockCombinationException.java to see how easy it is to create a specific exception
type.
In this first exercise we gave you shell code with comments. In this exercise you will create
the class from scratch; you should follow good style guidelines and add your own comments.
At a minimum document your class with @author tag, and document all methods including
parameters and return values. See the Combination class for example.
Exercise 2
The Lock class should have fields representing the combination, an upper limit for its dial,
and an indicator which states whether or not the Lock is open. Implement the following
methods in the Lock class.
1. Create a constructor that receives an int upper bound and a Combination object. If
the Combination is within the range of the upper bound, then it should set its own combination to the input. Otherwise, it should throw an InvalidLockCombinationException.
Furthermore, all locks should be open when created.
2. A method named getDialLimit which returns an int representing the dials upper
limit.
3. A method named open which receives a Combination and returns a boolean representing whether or not the lock is open. If the received Combination equals the
lock’s Combination, then set the lock’s state to open. If the lock is already open,
then lock will remain open regardless of the received Combination. Hint: use
Combination.equals(otherCombination) to check if two combinations are equal.
4. A method named close that sets the lock’s state to closed and returns nothing.
5. A method named isOpen that returns a boolean that indicates whether or not the
lock is open.
Test your code against LockTest.java.
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Exercise 2 Complete
Run:
git add .
git commit -m “Completed exercise 2”
git push origin master
2.3 Lock with Reset
We will create two methods in the Lock class called resetNaive and resetRetry.
Exercise 3
Implement the following methods in the Lock class.
1. void resetNaive()
Using JOptionPane.showInputDialog, get a String combination from the user and if
it’s not null, grab the 3 numbers. If the String is null, you don’t want to do anything.
(This allows the user to cancel!) Use a Scanner to scan the String, and extract the 3
integers. See https://docs.oracle.com/javase/8/docs/api/java/util/Scanner.
html#nextInt-int- for a list of potential exceptions that may be thrown if the string
is not formatted properly. You do NOT need to catch these here.
Create a new Combination using the three numbers, and if the combination is within
the dial limit, that becomes the Lock’s combination. If the combination is invalid,
it throws an InvalidLockCombinationException. This method should throw the
exception, but not catch it. Sometimes we want to handle exceptions, and sometimes
we want them to pass a message to another method, which is the case here.
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2. void resetRetry()
While a good combination has not been found, keep trying to get one (hint: use
resetNaive). If asking for a combination using resetNaive throws an
InvalidCombinationException, use JOptionPane.showMessageDialog to display the
message “Type 3 integers in the range [0..R]” where R is your dial limit set by the
constructor. If asking for a combination throws any other exception error (e.g. one
from Scanner), use JOptionPane.showMessageDialog to display the message “Type
3 integers separated by spaces”. (These dialogues must be exact). Keep trying to get
a good combination until a good combination is found, then that becomes the Locks
combination.
Exercise 3 Complete
Run:
git add .
git commit -m “Completed exercise 3”
git push origin master
3 Common Mistakes
1. Ensure that the constructor for Combination stores the combination in the numbers
array. Otherwise, this will break the equals method which will cause tests to fail.
2. Ensure that InvalidLockCombinationException extends Exception.
3. In resetRetry, be sure to invoke resetNaive as opposed to reimplementing resetNaive’s
functionality in resetRetry.
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4. Ensure that your messages are exactly as the lab specifies, and use the classes that the
lab tells you to use!
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