Description
1 Introduction
The focus of this lab is to define comparator methods for a class. A comparator is a method that compares two objects of the same type and returns whether or not another object is “less than”, “equal to”, or “greater than” the object that called the method. Examples of comparators are Java’s <=, ==, >=, Comparable.compareTo(T o), and Object.equals(Object o).
2 Exercises
Fork and clone the cpsc250l-lab06 repository in the cpsc250-students group.
2.1 Person
In this exercise, you will create a class that implements the Comparable interface. Exercise 1 Create a class called Person that implements the Comparable interface. The Person class c 1 should have a single field of type String that will store the Person’s name. Implement the following methods.
1. public Person(String _name) This constructor should set the Person’s name to the _name parameter.
2. public String getName() This method returns the Person’s name.
3. public void setName(String _name) This method changes the Person’s name to the _name parameter.
4. public Person copy() This method returns a new Person with the same name as this Person. Override the following methods. 1. public int compareTo(Person other) This method returns the lexicographical comparison of this Person’s name and other’s name. 2. public boolean equals(Object other) This method returns whether or not other is the same as this Person. If other.getClass does not equal Person, return false. Otherwise, return whether or not their names are equal. Test your code against PersonTest.java. Do NOT proceed to the next exercise until all tests pass. Exercise 1 Complete 2 Run: git add . git commit -m “Completed exercise 1” git push origin master
2.2 Party Exercise
2 Create a class called Party with the following fields. 1. An ArrayList of invited people. 2. An ArrayList of people who RSVP’d yes. 3. An ArrayList of people who RSVP’d no. Implement the following methods. 1. public void addInvited(Person p) This method adds a copy of p to the list of invited people. If p is already in the list, this method does nothing. 2. public ArrayList getInvited() This method returns a deep copy of the list of invited people. A deep copy of a list is another list with copies of the original list’s elements in the same order as the original. 3 CPSC 250L Lab 6
3. public void addRSVP(Person p, boolean accepted) If p is invited, this method will add p to the appropriate list. Specifically, if p was invited and is accepting the invitation, a copy of p should be added to the list of people who RSVP’d “yes”. Otherwise, if p was invited and is not accepting a copy of p should be added to the list of people who RSVP’d “no”. Additionally, a Person should be able to change their RSVP. Moreover, the list of people who RSVP’d “yes” and the list of people who RSVP’d “no” should be mutually exclusive. That is no Person should be on both the “yes” list and “no” list at the same time. Furthermore, neither list should contain two copies of the same Person.
4. public ArrayList getRSVP(boolean accepted) If accepted is true, this method returns a deep copy of the “yes” list. Otherwise, it returns a deep copy of the “no” list. 5. public boolean equals(Object o) If o is not a Party object, returns false. If this Party’s invited, “yes”, and “no” lists contain the same elements as o’s invited, “yes”, and “no” lists respectively then it returns true. Otherwise, it returns false. Test your code against PartyTest.java. Exercise 2 Complete Run: git add . git commit -m “Completed exercise 2” git push origin master 4 CPSC 250L Lab 6
3 Common Mistakes
Some solutions to common mistakes are as follows. 1. To get the lexicographical comparison of two String objects, use the String.compareTo(String) method. 2. Two objects are equal if and only if compareTo returns 0. 3. In the getter methods for Party, you must return a deep copy of the desired list. To do so, create a new list and iterate through the old one, adding a copy of each Person to the new list. 4. Be sure that when you move a Person from the “yes” list to the “no” list or vice-versa, you remove it from the old list. 5. Ensure that you do not add a Person to any list twice! 5 CPSC 250L Lab 6
