Question

I can’t see where I’m going wrong with this one, I want it to display the frequencies of the survey’s result but all I get is zeros, for example if I enter 1,1,2,2,5 I want it to output:

Displaying response frequencies...
1   2
2   2
3   0
4   0
5   1

but instead I get this:

Displaying response frequencies...
1   0
2   0
3   0
4   0
5   0

here is my main method:

import java.util.Scanner;
public class SurveyTester {

    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);

        System.out.println("How many people took the survey?");
        int numPeople = input.nextInt();
        Survey s = new Survey(numPeople);
        int nextResponse;
        for (int i = 0; i < numPeople; i++)
        {
            System.out.print("Input the next survey response (values 1-5):");

            nextResponse = input.nextInt();
            s.addResponse(nextResponse);
        }

        System.out.println("Displaying all responses...");
        s.displayAllResponses();
        System.out.println("Displaying response frequencies...");
        s.displayResponseFrequencies();
     }

}

here is my class:

public class Survey
{
    private int numResponses;
    private int maxResponses;
    private int[] responses;
    private int[] frequencies;
    private final int NUM_RESPONSES = 5;

    public Survey(int nResponses)
    {
        maxResponses = nResponses;
        numResponses = 0;
        responses = new int[nResponses];
        frequencies = new int[NUM_RESPONSES]; // There are 5 possible responses to the survey
    }

    public void addResponse(int response)
    {
        // This method stores the response
        // passed in the parameter 'response'
        // to the next free space in the array

        {
            responses[numResponses]= response;
        }

        numResponses++;
    }


    public void displayAllResponses()
    {
        // This method displays on the screen
        // all the responses to the survey

        for (int i=0; i<maxResponses; i++)
        {
        System.out.print(responses[i] + " ");
        }

        System.out.println("");
    }


    public void calculateResponseFrequencies()
    {
        // This method calculates the number of
        // responses for each possible answer
        // to the survey, 1, 2, 3, 4 or 5
        // It stores the frequencies in the
        // array 'frequencies'

        for (int i=1; i<=maxResponses; i++)
        {
            if (responses[i] == 1)
            {
                frequencies[1]++;
            }

            else if (responses[i] == 2)
            {
                frequencies[2]++;
            }

            else if (responses[i] == 3)
            {
                frequencies[3]++;
            }

            else if (responses[i] == 4)
            {
                frequencies[4]++;
            }

            else if (responses[i] == 5)
            {
                frequencies[5]++;
            }
        }
    }

    public void displayResponseFrequencies()
    {
        // This method displays the response
        // frequences for each of the possible
        // response, 1, 2, 3, 4 or 5

        for (int i=0; i<frequencies.length; i++)
        {
        System.out.println((i+1) + "\t" + frequencies[i]);
        }
    }

}

Answer 1

You are not doing anything with your frequencies array. In you your addResponse method, you need to get the appropriate value and increment it. Add a statement like

frequencies[response-1] = frequencies[response-1] + 1;

Note you can do this with 2 arrays, as you are, especially for learning, but a lot of Java developers would use a Map implementation for this sort of thing, where the keys are the entered values and the values are the frequencies. Keeps all the data in one data structure.