Java

OOP GUIDE / WORK

DIGITS CLASS

Topics

• Class design
• ArrayLists

Source

• This question was part of the 2017 AP exam free response questions. You can find a link to all free response questions on the previous page.

TASK – PART 1 – SETUP – DIGITS CLASS STARTER CODE

No solution required.

TASK – PART 2 – WORK

Here is my solution:

import java.util.ArrayList;

public class Digits

{

/** The list of digits from the number used to construct this object.

* The digits appear in the list in the same order in which they appear

* in the original number.

*/

private ArrayList<Integer> digitList;

/** Constructs a Digits object that represents num.

* Precondition: num >= 0

*/

public Digits(int num)

{

digitList = new ArrayList<Integer>();

if (num == 0)

digitList.add(0);

while(num != 0)

{

int digit = num % 10;

digitList.add(0, digit);

num = num / 10;

}

}

/** Returns true if the digits in this Digits object are in strictly increasing order;

* false otherwise.

*/

public boolean isStrictlyIncreasing()

{

if (digitList.size() < 2)

{

return true;

}

else

{

for (int i=0; i<digitList.size()-1; i++)

{

if (digitList.get(i) >= digitList.get(i+1))

{

return false;

}

}

return true;

}

}

public String toString()

{

return digitList.toString();

}

}

TASK – PART 4 – TESTING YOUR CLASS

No solution required.