AP Computer Science Homework Set 4 Arrays and ArrayLists of ...

AP Computer Science 

Homework Set 4 

Arrays and ArrayLists of Objects 

P4A. Write a class definition for a MyPod object that stores information about your 

personal music player. Class MyPod should include the following: 

a. an instance variable for its color, 

b. an instance variable for its memory capacity (in GB), 

c. an instance variable of type array that can hold 3 Song objects called 

“songLibrary” that represents all songs in the MyPod, 

d. a zero-argument and multi-argument constructor to initialize all instance 

variables. 

f. a toString() method to display the object’s instance variables in a userfriendly 

format. 

Write a MyPodDriver to perform the following: 

a. create a MyPod object carPod, 

b. initialize its instance variables using its multi-argument constructor. Pick your 

color, memory capacity, and songs to populate your pod with (this can be 

hardcoded in its constructor…no JOptionPane needed here) 

c. print out the information for each MyPod using the toString() method of 

the MyPod class. Use a for-each loop instead of the typical for loop. 

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AP Computer Science – HW Set 4 Programs 

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P4B. Write a program that creates a “ClockStore” class that is able to hold 

“Clock” objects. You should reuse the Clock class from the previous chapter. 

The class should meet the following requirements: 

1. Write a class “ClockStore” that consists of a private array called 

“clocksInStock” that can hold 3 Clock objects. 

2. Create an instance of class “ClockStore” and populate it with three Clock 

objects using the Clock’s constructor. You set the time for each Clock. 

Here’s a sample demonstrating how to place a Clock in the array at position 

“0”: 

clocksInStock[0] = new Clock( 12, 30, 45 ); 

4. Write a processor method mostSeconds() that returns index of the Clock 

that has the highest total seconds as calculated by the Clock method 

totalSeconds(). The ClockStore method mostSeconds() should 

have the following header: 

int mostSeconds() 

5. Write a toString() method that traverses the array of Clocks using a foreach 

loop. This should print the time of each clock using each Clock’s 

toString() method. 

6. Write a driver class “ClockDriver” that tests the above methods. 

P4C. Write a program that creates a “Roster” class that is able to hold 

“Student” objects. You should reuse the Student class from the previous 

chapter. 

The class should meet the following requirements: 

1. Write a class “Roster” that consists of a private array of Students. 

2. Create an instance of class “Roster” and populate it with three Student 

objects. 

3. Write a Roster findStudentWithMaxGPA() method that traverses the 

array with a for loop and returns out the name of the student with the max 

GPA. 

4. Write a Roster toString() method prints the name of the student with the 

maximum GPA (via calling the method findStudentWithMaxGPA(). 

5. Write a driver class “RosterDriver” that tests the above methods. 

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P4D. Write a program that creates an ArrayList of String objects that will hold 

the names of members of your family. After populating the ArrayList, perform 

the following: 

a. Print the number of elements in the ArrayList using the ArrayList 

“.size()” method. This should be consistent with the number of names in 

the ArrayList. 

b. Use a for loop to traverse the ArrayList and print the name of each 

person on a separate line. 

c. Use a separate for-each loop to traverse the ArrayList and print the 

name of each person on a separate line. 

See LewTube for demonstrations on how to create and use ArrayLists and all of 

its methods. The line of code below shows how to create an ArrayList of 

Strings: 

ArrayList myFamily = new ArrayList() 

Note that you can create an ArrayList of any type. For example, you can create an 

ArrayList of MySongs as follows: 

ArrayList playList = new ArrayList() 

P4E. Write a program that creates an ArrayList of String objects that will hold 

the names of the universities to which you are applying (include at least three schools 

that contain 4 letters…UC’s are easy: UCLA, UCSD, UCSB, or Yale, MITT (the 

baseball university, or SWIM (the aquatics university). After populating the 

ArrayList with at least 5 schools, perform the following: 

a. Print the number of elements in the ArrayList. This should be consistent 

with the number of schools in the original ArrayList. 

b. Use a for-each loop to traverse the ArrayList and print the name of each 

school on a separate line. 

c. Use a for loop (not a for-each loop), to remove all the schools that have a 

length of 4. Make sure to test the situation where there are two consecutive 

schools of length “4” in your ArrayList. 

d. Print the number of elements in the ArrayList after the removal. Again, this 

should be consistent with the number of schools remaining in the list. 

e. Finally, print the names of the schools remaining in the list. Were all of the 4 

letters schools properly removed? 

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P4F. Let’s upgrade the MyPod class. Create a MyPod2 class that uses an 

ArrayList to store Songs instead of an array. Provide the same functionality as 

in P4A. 

P4G. Finally, let’s upgrade the Roster class so that it can accommodate “adding” 

and “dropping” Students from a roster. Write a Roster2 class called 

“apComputerScience” that meets the following requirements: 

a. Roster2 should use an ArrayList called myStudents (instead of an 

array) to store Student objects. 

b. A processor method called “addStudent” should be included that will add a 

given Student to the ArrayList myStudents. The method 

addStudent should have the following header: 

public void addStudent ( Student newStudent ) 

Note that the addStudent method will ultimately call the ArrayList’s 

.add() method since Student objects are stored in the ArrayList of 

myStudents. 

c. A processor method in the Roster class called “dropStudent” with the 

following header: 

public void dropStudent ( String lastName ) 

The method dropStudent should remove the student with the given last 

name. For example, the following line of code will remove the student “Lew” 

from the ArrayList myStudents: 

period1.dropStudent( “Lew” ); 

d. Write a Roster2Driver that performs the following: 

i. Creates a Roster2 object called “apComputerScience”, 

ii. Adds three students using the “addStudent” method, 

iii. Prints “period1” using Roster2’s toString() method to verify 

all “added” Students have indeed been added, 

iv. Calls the “dropStudent” method to drop one of the students in the 

ArrayList myStudents (i.e. any one of the Students in the 

class), and 

v. Prints “apComputerScience” again to view the revised list of 

Students in the “apComputerScience”. 

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By the end of the lesson students should be able to: 

a. Write a class definition that includes instances of another class (class 

composition) 

b. Write an object method whose output depends on the object’s instance 

variables. 

c. Use arrays and ArrayLists in a class and be able to use either a for or 

for-each loop to traverse the array or ArrayList. 

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