Question

This question involves the implementation of the TriangleNumberTracker class which is used to keep track of triangle numbers. The triangle numbers form a sequence, the first 5 terms of which are shown below. This first term of this sequence is 1, and subsequent terms are found by incrementing the previous term by the term number.

Term number	1	2	3	4	5
Triangle Number	1	3	6	10	15
Explanation		1 + 2 = 3	3 + 3 = 6	6 + 4 = 10	10 + 5 = 15

A TriangleNumberTracker object is created with an integer term number which determines the starting term to which the tracker refers. For example if the term number is 4, the tracker begins at the 4th triangle number, which is 10.

The TriangleNumberTracker class provides a constructor and the following methods.

• currentTriangle which returns the triangle number which the tracker points at as an int.

• nextTriangle which changes the tracker to point at the next triangle number.

• prevTriangle which changes the tracker to point at the previous triangle number, unless it already points at the first triangle number (1).

The following table contains a sample code execution sequence and the corresponding results.

Statements and Expressions	Value Returned (blank if no value)	Comment
TriangleNumberTracker t = new TriangleNumberTracker(4);		t is initialized pointing to the 4th triangle number
t.currentTriangle();	10	The 4th Triangle number is 10
t.nextTriangle();		Moves current triangle number to the 5th
t.currentTriangle();	15	The 5th Triangle number is 15
t.nextTriangle();		Moves current triangle number to the 6th
t.currentTriangle();	21	The 6th Triangle number is 21
t.prevTriangle();		Moves current triangle number to the 5th
t.prevTriangle();		Moves current triangle number to the 4th
t.prevTriangle();		Moves current triangle number to the 3rd
t.currentTriangle();	6	The 3rd Triangle number is 6
t.prevTriangle();		Moves current triangle number to the 2nd
t.prevTriangle();		Moves current triangle number to the 1st
t.currentTriangle();	1	The 1st Triangle number is 1
t.prevTriangle();		Does nothing as current triangle number is already 1st (lowest possible)
t.currentTriangle();	1	The 1st Triangle number is 1

Write the complete TriangleNumberTracker class including the constructor and any required instance variables and methods. Your implementation must meet all specifications and conform to the example.

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Please note: The code for these FRQ activities has no main method, so it will not run in the Run Code area of your programming environment. If you would like to run your code, you will need to add a main method to your program. To score your code, you cannot have a main method in your program.

Answer 1

// defining class TriangleNumberTracker

public class TriangleNumberTracker

{

    // 2 instance variables to keep record of term number and triangle number

    int termNumber;

    int triangleNumber;

    

    // constructor of class

    public TriangleNumberTracker(int n)

    {

        termNumber = n; // initializing termNumber with provided n

        triangleNumber = 0; // initialize triangleNumber with 0

        // adding terms to calculate triangleNumber

        for(int i=1; i<=termNumber; i++)

        {

            triangleNumber += i;

        }

    }

    // method currentTriangle which returns the triangle number which the tracker points

    public int currentTriangle()

    {

        return triangleNumber;

    }

    // nextTriangle which changes the tracker to point at the next triangle number

    public void nextTriangle()

    {

        termNumber += 1;

        triangleNumber += termNumber;

    }

    

    // prevTriangle which changes the tracker to point at the previous triangle number

    public void prevTriangle()

    {

        if(termNumber > 1){

            triangleNumber -= termNumber;

            termNumber -= 1;

        }

    }

    

    // defining main with provided sequence of code

    public static void main(String[] args)

    {

        TriangleNumberTracker t = new TriangleNumberTracker(4);

        System.out.println(t.currentTriangle());

        t.nextTriangle();

        System.out.println(t.currentTriangle());

        t.nextTriangle();

        System.out.println(t.currentTriangle());

        t.prevTriangle();

        t.prevTriangle();

        t.prevTriangle();

        System.out.println(t.currentTriangle());

        t.prevTriangle();

        t.prevTriangle();

        System.out.println(t.currentTriangle());

        t.prevTriangle();

        System.out.println(t.currentTriangle());

    }

}