Java eliminating duplicates in an Array

Question

Can't get this working, it's supposed to sort any number of numbers input by a user and then eliminate duplicates. Right now the program is only printing 0's, but it should be printing an array with no duplicates. I have to do this the hard way as well, I can't use Java's built in sorting or array copying methods. Why does my code only print 0's, and how can I fix it?

package Lab_10;

import java.util.Scanner;
public class Eliminating_duplicates
{
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter the number of numbers: ");
        int numOfNums = input.nextInt();
        int[] list = new int[numOfNums];
        int[] newList = new int[numOfNums];
        for( int x = 0; x < list.length; ++x)
        {
            while(numOfNums != -1 && x < list.length)
            {
                System.out.print("Enter value " + (x + 1) + ": ");
                int value = input.nextInt();
                list[x] = value;
                ++x;
            }
        }
        sortList(list);
        System.out.println("Here is the sorted list: ");
        for (int x = 0; x < list.length; ++x)
        {
            System.out.println(list[x]);
        }
        eliminateDuplicates(list);
        System.out.println("Here is the list without duplicates: ");
        for (int x = 0; x < newList.length; ++x)
        {
            System.out.println(newList[x]);
        }
    }
    public static void sortList(int[] list)
    {
        int temp;
        boolean madeASwap = true;
        int lastIndex = list.length-1;
        while (madeASwap)
        {
            madeASwap = false;
            for (int x = 0; x < lastIndex; ++x)
            {
                if (list[x] > list[x + 1])
                {
                    temp = list[x];
                    list[x] = list[x + 1];
                    list[x + 1] = temp;
                    madeASwap = true;
                }
            }

        }
    }
    public static int[] eliminateDuplicates(int[] list)
    {
        int end = list.length;
        for (int i = 0; i < end; i++)
        {
            for (int j = i + 1; j < end; j++) {
                if (list[i] == list[j]) {
                    for (int k = j + 1; k < end; k++, j++) {
                        list[j] = list[k];
                    }
                    --end;
                    --j;
                }
            }
        }
        int[] newList = new int[end];
        return newList;
    }
}

Answer 1

You don't actually copy the values over.

int[] newList = new int[end];
return newList;

This creates a new list containing only zeroes, which gets ignored. You can copy them over using something like:

int[] newList = new int[end];
for (int i = 0; i < end; i++) {
  newList[i] = list[i];
}
return newList;

The reason you think this works, I believe, is that you also have an array called newList in your main method, but you never assign anything to it.

int[] newList = new int[numOfNums];

This never gets accessed again until you try to print it's contents, which are, again, by default, all zeroes.

Make sure to save the returned array by doing this:

newList = eliminateDuplicates(list);

None of this matters, though, because your modification of the array is destructive, which means that your array is different after calling the eliminate duplicates method. Here's the fixed program:

import java.util.Scanner;

public class Eliminating_duplicates {
  public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    System.out.print("Enter the number of numbers: ");
    int numOfNums = input.nextInt();
    int[] list = new int[numOfNums];
    int[] newList = new int[numOfNums];
    for (int x = 0; x < list.length; ++x) {
      while (numOfNums != -1 && x < list.length) {
        System.out.print("Enter value " + (x + 1) + ": ");
        int value = input.nextInt();
        list[x] = value;
        ++x;
      }
    }
    sortList(list);
    System.out.println("Here is the sorted list: ");
    for (int x = 0; x < list.length; ++x) {
      System.out.println(list[x]);
    }
    newList = eliminateDuplicates(list);
    System.out.println("Here is the list without duplicates: ");
    for (int x = 0; x < newList.length; ++x) {
      System.out.println(newList[x]);
    }
  }

  public static void sortList(int[] list) {
    int temp;
    boolean madeASwap = true;
    int lastIndex = list.length - 1;
    while (madeASwap) {
      madeASwap = false;
      for (int x = 0; x < lastIndex; ++x) {
        if (list[x] > list[x + 1]) {
          temp = list[x];
          list[x] = list[x + 1];
          list[x + 1] = temp;
          madeASwap = true;
        }
      }

    }
  }

  public static int[] eliminateDuplicates(int[] list) {
    int end = list.length;
    for (int i = 0; i < end; i++) {
      for (int j = i + 1; j < end; j++) {
        if (list[i] == list[j]) {
          for (int k = j + 1; k < end; k++, j++) {
            list[j] = list[k];
          }
          --end;
          --j;
        }
      }
    }
    int[] newList = new int[end];
    for (int i = 0; i < end; i++) {
      newList[i] = list[i];
    }
    return newList;
  }
}

Answer 2

you need to include this to return the proper int array in your eliminateduplicates function:

   int[] newList = new int[end];
    for (int l = 0; l < end; l++) {
        newList[l] = list[l];
    }
    return newList;

and then you need to catch it as well:

by that I mean instead of this:

 eliminateDuplicates(list);

you need this:

 list = eliminateDuplicates(list);

Answer 3

public static void sortList(int[] list)

while(numOfNums != -1 && x < list.length)

eliminateDuplicates(list);

These are the 3 things I picked out from your code, mind you I picked them out pretty quickly too. We'll start from the top:

public static void sortList(int[] list)

Literally does nothing. Why? Simple! It returns nothing. For it do return SOMETHING it needs to have a return type of int[] in your case.

while(numOfNums != -1 && x < list.length)

When initializing arrays like you are, you are giving it it's array.length value inside of the brackets. A list with 0 items is worthless to your code. Heck, a list with 1 item is worthless to your code. So maybe change it to:

while(numOfNums > 1 && x < list.length)

Lastly:

eliminateDuplicates(list);

This, also does nothing. Yet again, why? Alas, yet again, it's simple. It may be returning an int[] but you do nothing with what it returns. To use it change it to:

array = eliminateDuplicates(list);

or probably better suited to your case:

newList = new int[eliminateDuplicates(list).length]; newList = eliminateDuplicates(list);

This will set it to the exact size of what the list will be, and after that it just sets it equal to the array that is returned.