Removing an element from Array on Runtime in Java

Question

Is there a way to remove an element from a an Array on Runtime?

For Example:

int[] num =  {8, 1, 4, 0, 5};

Output:
Enter the Index: 0
1, 4, 0, 5
Enter the Index: 3
1, 4, 0
Enter the Index: 1
4, 0;

I know that you cannot resize an Array's length once it is initialized and in this kind of sample problem, using an ArrayList is much more practical. However, is there a way to do this kind of problem by using just an array?

I've managed to remove one element and display the array -1 by creating new array and copying the original array's values in it. But the problem is, in the next iteration in the Output I can still remove an element but the size does not change.

This is what happens:

int[] num =  {8, 1, 4, 0, 5};

Output:
Enter the Index: 0
1, 4, 0, 5  // in the first loop it goes as I want it.
Enter the Index: 2
1, 4, 5, 5  // this time array's length is still 4 and just duplicates the last value
Enter the Index: 1
1, 5, 5, 5  // length is still the same and so on.

This is my code in removing an element from an array:

public static int[] removeElement(int index, int[] n) {

    int end = n.length;

    for(int j = index; j < end - 1; j++) {
        n[j] = n[j + 1];            
    }
    end--;

    int[] newArr = new int[end];
    for(int k = 0; k < newArr.length; k++) {
        newArr[k] = n[k];
    }

    displayArray(newArr);        

    return newArr;
}

public static void main(String[] args) {
     Scanner input = new Scanner(System.in);
     int[] num = {8, 1, 4, 0, 5};

     for(int i = 0; i < num.length; i++) {
          System.out.print("Enter the Index: ");
          int index = input.nextInt();
          removeElement(index, num);
     }
}

public static void displayArray(int[] n) {
     int i = 0;
     for(; i < n.length - 1; i++) {
          System.out.print(n[i] + ", ");
     }
     System.out.print(n[i]);
}

Is there a trick on how to do this on Arrays? Or do I really have to use ArrayList?

I see your array only contains positive numbers. Maybe you can replace the last number by -1, so instead when displaying the array, you run over the array until you arrive at value -1. — Dominique
– Dominique, Commented Dec 20, 2018 at 8:45
@robert, it's a suggestion.. Its better to go with Java Collections... — PrabaharanKathiresan
– PrabaharanKathiresan, Commented Dec 20, 2018 at 9:14

Eran · Accepted Answer · 2018-12-20 08:47:36Z

7

You are discarding the new array returned by removeElement.

Change your loop to:

for(int i = 0; i < num.length; i++) {
     System.out.print("Enter the Index: ");
     int index = input.nextInt();
     num = removeElement(index, num);
}

answered Dec 20, 2018 at 8:47

Eran

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Comments

HaroldSer · Accepted Answer · 2018-12-20 08:51:19Z

1

From your code, you are not actually removing an element from an array. You are in fact creating a new array, with size 1 less than previous array and filling the new array with the old array's remaining values.

In addition, your logic to remove an element from the old array is wrong. To start, your old array still has the same size, all you are doing is replace the array's element at index position with the element at index+1 position.

answered Dec 20, 2018 at 8:51

HaroldSer

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ETO · Accepted Answer · 2018-12-20 09:03:50Z

1

You can try this code:

public static int[] removeElement(int index, int[] arr) {
    int length = arr.length - 1;
    int[] res = new int[length];
    for(int i = 0; i < index; i++) {
        res[i] = arr[i];
    }
    for(int i = index; i < length; i++) {
        res[i] = arr[i + 1];
    }
    return res;
}

The idea of code snippet above is to copy the array to a new one (with length less by one) skipping the element we'd like to remove

edited Dec 20, 2018 at 9:03

answered Dec 20, 2018 at 8:52

ETO

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